US3081598A - Drives for centrifugals - Google Patents

Description

R. C. GOODWIN DRIVES FOR CENTRIFUGALS March 19, 1963 5 Sheets-Sheet 1 Filed Oct. 18, 1960 A sE INVENTOR RALPH c. eooowm ATTQlEY March 19, 1963 R. c. GOODWIN 3,081,598

DRIVES FOR CENTRIFUGALS Filed Oct. 18, 1960 5 Sheets-Sheet 5 V v as M4- INVENTOR. f I RALPH c. eooowm L ATTORNEY.

March 19, 1963 R. c. GOODWIN 3,081,598

DRIVES FOR CENTRIFUGALS Filed Oct. 18, 1960 5 Sheets-Sheet 4 INVENTOR RALPH C. GOODWIN ATTOR Y March 19, 1963 R. c. GOODWIN 3,

DRIVES FOR CENTRIFUGALS Filed Oct. 18, 1960 5 Sheets-Sheet 5 x Q Q 55g 3 Eg D P/L OTED PEL/EF PILOTED PE4/EF 8 INVENTOR. RALPH c. eooowm A TORNEY.

United States Patent 3,081,598 DRIVES FOR CENTRIFUGALS Ralph C. Goodwin, Hamilton, Ohio, assignor to The Western States Machine Company, Hamilton, Ohio, a corporation of Utah Filed Get. 18, 196i), Ser. No. 63,368 43 Claims. (CI. 60-53) The present invention relates generally to heavy duty rotary drive assemblies, and more particularly is directed to drives for centrifugals or extractors of the kind used for removing or separating liquids from bulk solids, for example, as in the chemical industry or in the refining of sugar, or for removing excess water or other liquid cleaning agents from clothing and other fabrics in laundries and cleaning establishments.

The basket of a centrifugal or extractor of the described character is frequently driven by an electric motor directly coupled to the basket shaft, or by a belt and pulley transmission from an electric motor which is ofiiset relative to the basket shaft. Frequently the basket is rotatably supported by a structure that permits gyratory movement of the basket in the event of unbalanced loading thereof, thereby to avoid the transmission of vibrations to the fixed supporting structure of the centrifugal, and the provision of an electric motor for driving the basket makes the relatively large mass of the motor a part of the assembly undergoing gyratory movement, and thereby further increases the vibratory energy that needs to be absorbed. Further, if the large mass of the electric motor is offset relative to the basket shaft and the rotary drive is transmitted to the basket shaft by way of a belt and pulley transmission, the suspended mass is not symmetrical about the axis of the basket so that an elliptical gyratory movement results from unbalanced loading of the basket, and such elliptical gyratory movement gives rise to undesirable tilting of the basket axis.

The use of an electric motor for rotating the basket of a centrifugal of the described character generally requires the positioning of the motor above the basket if the latter is to be provided with a bottom discharge for solids, as an electric motor having a sufficiently large output to drive the basket will have relatively large dimensions and therefore take up the space required for the bottom discharge when it is directly coupled to the basket shaft below the basket. On the other hand, if the relatively large electric motor is disposed to one side of the basket and the rotary drive is transmitted to the lower end of the basket shaft below the basket by way of a belt and pulley transmission, the transmission belts present a maintenance problem, and braking of the rotation of the basket is less reliable than with a directly coupled drive. Further, the conventional overhead drives of centrifugal baskets tend to disadvantageously increase the height of the centrifugal, and thereby limit the building structures in which such machines can be installed. The overhead drives also clutter the space above the centrifugal basket, thereby interfering with the performance of operations around the basket curb, and, in vapor tight machines, there is the problem of sealing the spindle or shaft opening in the curb top.

Accordingly, it will be seen that a desirable drive for centrifugals or the like should provide a driving component directly coupled to the basket shaft and having relatively small mass and dimensions symmetrical with respect to the basket axis so that the basket can be suspended for gyratory movement in the event of unbalanced loading thereof without having such driving component adversely affect the conditions of the gyratory movement. Further, such a driving component can be disposed below the basket without interfering with the bottom discharge of solids from the basket. Where the 3,081,598 Patented Mar. 19, 1963 ice centrifugal is provided with a discharger of the kind havmg a shoe which remains within the basket, for example, as disclosed in United States Letters Patent No. 2,667,974, issued February 2, 1954, to Joseph Hertrich, the centrifugal drive should also be capable of rotating the basket at a high speed in one direction during normal centrifuging of the solids, and of rotating the basket in the opposite direction, at a relatively slow controlled speed, during discharging of the solids, so that, with the shoe of the discharger extending generally in the direction of the high speed rotation, the shoe can dig into the wall of solids only during discharging and can be safely maintained in the basket during centrifuging.

It is an object of the present invention to provide a drive for centrifrugals or the like having the above described advantageous characteristics.

In accordance with an aspect of this invention, a drive for centrifugals or the like includes a hydraulic, positive displacement motor directly coupled to the shaft of the basket or other assembly to be rotated, and a remote power unit including an electric motor, or other prime mover driving at least one hydraulic pump by which hydraulic fluid under pressure is fed through conduit-s to the positive displacement motor for the purpose of operating the latter.

A hydraulic drive of the described character has the advantages of providing speed adjustment, constant horsepower or constant torque acceleration, forward and reverse rotation at different speeds and hydraulic braking of the driven assembly, in a less expensive drive than is otherwise available. Further, the relatively small size and mass of the hydraulic motor make it possible to position the motor under the basket and to directly couple the motor to the basket shaft in a centrifugal of the link suspended type. Even when applied to aconventional overhead suspended type centrifugal, the small dimensions of the hydraulic motor reduce the head room requirements.

It is a more specific object of the invention to provide a hydraulic drive for centrifugals or the like which is capable of effecting high speed forward rotation, for example, during spinning of the centrifugal basket, and also capable of braking such high speed forward rotation so that the basket is rapidly brought to a standstill and thereafter rotat d at a relatively slow constant speed in the reverse direction, for example, during the discharging of solids from the basket.

Further objects are to provide hydraulic drives of the described character wherein small valves exert pilot control over large oil flows, and power peaks are maintained gelatively low while minimizing heating of the hydraulic uid'.

In accordance with another aspect of the invention, first and second conduits extend from the power unit to the hydraulic motor, and controls are provided to direct the how of hydraulic fluid under pressure through the first conduit to the motor and return the exhausted fluid from the motor through the second conduit during high speed forward rotation, and to direct fiuid under pressure to the motor through the second conduit for return from the motor through the first conduit during relatively slow reverse rotation, the first and second conduits having pres sure relief means associated therewith in order to prevent the build-up of excessive pressures therein, particularly during braking of the rotation of the motor. Thus, if the motor is initially effecting high speed forward rotation of the centrifugal basket, and the controls are then shifted to the position for braking and reverse rotation, the hydraulic motor initially acts as a pump and the pressure relief means associated with the second conduit establishes a limited back pressure in the latter which acts in the hydraulic motor to produce a predetermined braking torque until such time as the motor comes to a standstill and hydraulic fluid under pressure flows through the second conduit to the motor for effecting reverse rotation.

Since hydraulic, positive displacement motors of the type to be employed have leakage losses which progressively increase with increasing loads on the motor during slow rotation of the latter, the feeding of hydraulic fluid under pressure to the motor at a constant flow rate during the slow reverse rotation of the basket would result in a progressively decreasing speed of reverse rotation as the load on the motor increased, for example, as a result of the action of the discharging shoe cutting into the wall of solids in the basket. Accordingly, it is another object of the invention to provide a centrifugal drive of the described character wherein the rate of flow of hydraulic fluid under pressure to the motor during the relatively slow reverse rotation of the centrifugal basket is increased, either in a step-by-step or progressive fashion, in response to increases in the pressure of the hydraulic fluid, that is, in accordance with increasing load on the hydraulic motor thereby to maintain a substantially constant speed of reverse rotation.

A still further object of the invention is to provide a hydraulic drive for centrifugals or the like wherein means are provided for avoiding cavitation within the hydraulic motor as a result of the failure to maintain an adequate supply of hydraulic fluid to the motor in the event of a power failure while the basket is being rotated.

The above, and other objects, features and advantages of the invention, will be apparent in the following detailed description of illustrative embodiments thereof which is to be read in connection with the accompanying drawings forming a part hereof, and wherein:

FIG. 1 is a schematic view of a hydraulic drive for a centrifugal in accordance with a first embodiment of the present invention;

FIG. 2 is an enlarged, diagrammatic sectional view of a control valve included in the hydraulic drive of FIG. 1;

FIG. 3 is a view similar to that of FIG. 2, but showing the valve in another operating position;

FIG. 4 is also a view similar to that of FIG. 2, but showing the control valve in still another operating position;

FIG. 5 is a vertical sectional view of a variable volume hydraulic pump included in the hydraulic drive of FIG. 1;

FIG. 6 is a schematic view of a portion of a hydraulic drive for centrifugals which is a modification of the drive illustrated in FlG. 1;

FIG. 7 is an enlarged elevational view, partly broken away and in section, of a flow control device included in the modified drive of FIG. 6;

FIG. 8 is a schematic view of a hydraulic drive for centrifugals or the like constructed in accordance with another embodiment of the invention, and with a control valve included therein being shown in section;

FIG. 9 is a schematic view of a portion of a hydraulic drive for centrifugals which is a modification of the hydraulic drive of FIG. 8;

FIG. 10 is a schematic view showing another modification of the drive of FIG. 8; and

FIG. 11 is a schematic view of a hydraulic drive for centrifugals or the like constructed in accordance with still another embodiment of the invention.

Referring to the drawings in detail, and initially to FIG. 1 thereof, it will be seen that a hydraulic centrifugal drive embodying the present invention, and there generally identified by the reference numeral 10, includes an electric motor 11 which maybe mounted on the top of a hydraulic fluid storage tank 12, and which has the opposite ends of its shaft 13 connected, by couplings 1d and 15, respectively, to a main hydraulic pump it? and to an auxiliary hydraulic pump 17, with the pumps 16 and 17 h also being mounted on top of tank 12 so as to provide a compact power unit.

The relatively large main pump 16, which is intended to supply the hydraulic fluid under pressure for effecting the high speed forward rotation of the associated centrifugal basket or the like, is preferably of the type delivering a variable volume of fluid that is automatically adjusted in accordance with the demands of the circuit to which it is connected, for example, a pump of the type available from Racine Hydraulics and Machinery Inc, Racine, Wisconsin, under the designation Racine Model R Variable Volume Vane Pump. As shown in FIG. 5, such a pump may include a housing 18 with a shaft 19 mounted rotatably therein and supporting a rotor 29 having radial slots 21 slidably accommodating vanes 22 which are spring urged radially outward into sliding contact with the inner cylindrical surface of a shiftable inner casing 23. The inner casing 23 is suspended, from the top, by an assembly 24 and is movable horizontally with respect to the axis of shaft 19 from a position where the center of the inner cylindrical surface of casing 23 is aligned with the axis of shaft 19 to a position where there is a maximum eccentricity between the axis of shaft 19' and the center of casing 23. The pump housing 18 has a cylindrical extension 25 at one side, and a piston 26' is axially slidable in the extension 25 and is urged against the shiftable casing 23 by a governor spring 27 which bears against an adjustable abutment 28 carried by a screw 29 extending threadably through the outer end of extension 25.

It will be apparent that the spring 27 and piston 26 tend to shift casing 23 to a position of maximum eccentricity with respect to the axis of shaft 19, and a stop screw 36) extends threadably into housing 18 at a location diametrically opposed to piston 26 and is engageable by casing 23 for adjustably limiting the shifting move ment of the casing by spring 27.

The pump 16 is providel with an inlet 31 which receives fluid to be pumped from tank 12 by way of an inlet pipe 32 depending into the tank (FIG. 1), and the pump 16 further has an outlet 33 for delivering the hydraulic fluid under pressure. If it is assumed that shaft 19 is rotated at a substantially constant speed, it will be apparent that the volume enclosed between successive vanes 22 of the pump will be a maximum, and the fluid will be pumped at a maximum volumetric rate when there is a maximum eccentricity between the center of casing 23 and the axis of shaft 19. However, the pressure of the fluid being pumped acts against the inner surface of the casing 23 so that, when the output pressure is at a maximum, such pressure shifts casing 23 in the direction opposed to the force exerted by spring 27, thereby moving the center of casing 23 toward the axis of shaft 19 and correspondingly decreasing the volumetric rate at which the fluid is pumped. The relationship between the pressure of the pumped fluid and the volumetric rate at which the fluid is delivered is determined by the characteristics of the governor spring 27 and, in the illustrated embodiment of the invention, the governor spring 27 has been selected so as to maintain a substantially constant horse-power demand on the electric motor 11. Thus, spring 27 provides for the delivery of hydraulic fluid at a high pressure when the demand of the circuit or system is for a relatively low volume of fluid, thereby to provide a good acceleration torque, and to deliver the fluid at a relatively low pressure which provides an adequate torque for high speed spinning of the centrifugal basket, when there is a demand for the delivery of the fluid at a high volumetric rate during such high speed spinning.

It will be apparent that adjustments of the screw 29 can shift the range of pressures delivered by the pump to higher or lower levels, but will not basically alter thev pressure-volume relationship established by spring 27, whereas adjustment of the screw 30, which controls the maximum travel or shift of the casing 23, can vary the. upper limit of the volumetric rate at which hydraulic fluid;

is delivered, and thus the top speed of the centrifugal basket.

The output 33 of pump 16 is connected to a pipe or conduit 34 (FIG. 1) which has a piloted relief valve 35 interposed therein. The piloted relief valve 35 serves the dual function of limiting the pressure within pipe 34- and of unloading the related pump 16 when the output of the latter is not required for driving the associated centrifugal basket, and a piloted relief valve having such dual functions may be obtainel from the Denison Engineering Division, American Brake Shoe Company, Columbus, Ohio, under the designation RV40. Piloted relief valve 35 is also connected to a pipe 36 which opens into a return pipe 37 extending back to tank 12 and through which the output of pump 16 is dumped back to the tank when such output is not required, for example, when the centrifugal basket is being rotated in the reverse direction as hereinafter described in detail, or through which hydraulic fluid is dumped when the pressure in pipe 34 exceeds a predetermined, adjusted value for which the piloted relief valve 35 has been se. A pilot line 38 extends from valve 35 and loads the latter to limit the pressure in pipe 34 to a predetermined value, for example, to a pressure set at 1000 to 1250 pounds per square inch when the pilot line 38 is blocked, while the valve 35 is unloaded and effective to dump the output of pump 16 when pilot line 38 is open or unblocked.

Pipe 34 is connected, for example, by a coupling 39, to a flexible pipe or hose 40 which extends to the inlet 41 of a hydraulic, positive displacement motor 42, for example, a vane type motor of the kind available from the Denison Engineering Division, American Brake Shoe Company, Columbus, Ohio, under the designation THES'C. The identified motor is operated by a flow of hydraulic fluid of up to forty gallons per minute at a pressure of up to 1250 pounds per square inch during rotation in the forward direction, that is, when fluid under pressure is supplied thereto through the inlet 41, and such motor is intended to receive fiuid under pressure at a relatively small volumetric rate, for example, 5.7 gallons per minute, and at a relatively high pressure, for example, approximately 2000 pounds per square inch, when rotated in the reverse direction, that is, when fluid under pressure is supplied thereto through the normal outlet 43 and exhausted from the motor through the normal inlet 41. Of the above indicated relatively small volu metric rate supplied to normal outlet 43, a major portion, for example, approximately 4 gallons per minute, eifects the reverse rotation, while the remainder of the flow supplies theleakage through the motor 42 at high discharging pressure.

Since the motor 42 has a relatively small mass and dimensions in terms of the power that it can deliver to a rotary element to be driven thereby, such motor is ideally suited for direct coupling to the shaft of the basket of a centrifugal which may be of the kind disclosed in detail in the copending application for United States Letters Patent identified as Serial No. 62,713, filed October 14, 1960, by Ralph C. Goodwin and Thomas R. Laven. Such centrifugal is diagrammatically represented by broken lines on FIG. 1 and there generally identified by the reference numeral 44, and includes a basket 45 which is open at the top to receive the charge and has a bottom discharge opening. The basket is rotatably mounted on a shaft 46 supported in a manner to permit gyrato-ry movement of the basket when the loading of the latter is unbalanced, and the shaft of motor 42 is directly coupled to shaft 46 and disposed below the basket 45 in order to leave the curb top clear and to reduce the overall height of the centrifugal, while the small dimensions of motor 42 avoid any interference with the downward discharge of solids from the basket and the small mas of the motor avoids any adverse influence on the conditions of the gyratory movement of the basket.

The auxiliary pump 17 is of the type delivering the bydraulic fluid at a relatively high pressure, for example, i

2000 pounds per square inch, at a relatively small volumetric rate, for example, approximately 5.7 gallons per minute, and may be a vane type pump available from Denison Enginering Division, American Brake Shoe Com pany, Columbus, Ohio, under the designation TMOI. The inlet of pump 17 i connected to an inlet pipe '47 extending into tank 12 for withdrawing hydraulic fluid from the latter, while the outlet of pump 17 is connected to an Outlet pipe 48 which communicates with a piloted relief valve 49 similar to the piloted relief valve 35, but set to relieve the pressure in pipe 48 at a higher value, for example, at a pressure of 2000 pounds per square inch. Piloted relief valve 49 communicates with a pipe 50 which is connected, as by a coupling 51, to a flexible pipe or hose 52 extending to the outlet 43 of motor 42,

and a pilot line .53 extends from valve 49 and causes the latter to limit the pressure in pipes 43 and 50 to the adjusted value for which valve 49 is set when pilot line 53 is blocked, whereas piloted relief valve 49 is effective to dump the output of pump 17 into return pipe 37, by

way of a pipe 54, when pilot line 53 is open.

Pilot lines 38 and 53 are connected to a control valve generally identified by the reference numeral 55, and

which may be of the type having three operating positions available from Denison Engineering Division, American Nalve 55 further includes a valve body or spool 58 with a rod 59 extending from the spool out of housing 56 for actuation by a lever 69. The lever 66 may be in the form of a handle, as shown, for manual actuation, or it may be otherwise actuated, for example, by a solenoid or the like.

The spool 58 of valve '55 is formed so that, when in the position of FIG. 2, both pilot lines 38 and 53 communicate with return line 57, whereby both of the piloted relief valves 35 and 49 are unloaded and dump the outputs of the related pumps 18 and 17, respectively. With valve 55 in the position of FIG. 2, the basket 45 connected to motor 42 can either remain at rest, or, if the basket is rotating when the valve is placed in the position of FIG. 2, the basket can coast in the direction of the existing rotation. When spool 58 of valve 55 is shifted toward the right from the position shown in FIG. 2 to the position shown in FIG. 3, pilot line 53 continues to communicate with return line 57, while pilot line 38 is blocked so that piloted relief valve 49 is unloaded and continues to dump the output of its related pump 17, whereas the pressure on piloted relief valve 35 builds up to the main pump output pressure which i maintained.

With the valve in the position illustrated in FIG. 3, the output of punrp 16 is fed through pipe 34 and hose 4% to the inlet 41 of motor 42 to cause rotation of the latter in the forward direction at a relatively high speed, while the exhausted fluid is discharged through the outlet 43 of motor 42, and through hose 52, pipe 50, piloted relief valve 49, pipe 54 and pipe 37 back to tank 12.

When spool 58 of valve 55 is moved further to the left from the position of FIG. 2 to the position shown in FIG. 4, pilot line 33 is placed in communication with return line 57 While pilot line 53 is blocked so that piloted relief valve 35 is unloaded and dumps the output of pump 16, and piloted relief valve 49 is loaded and functions to limit thepressure of the fluid supplied from pump 17 through pipe 48. to the position of FIG. 4 while the basket is in highspeed forward rotation, motor 42 acts as a pump and relief valve 4% determines the value of the back pressure available in pipe 50 to exert a braking torque in the If valve 55 is shifted motor for arresting rotation of the basket until the latter has come to rest, whereupon the fluid supplied under pressure by the pump 17 causes relatively slow reverse rotation of the centrifugal basket.

On the other hand, if the valve 55 is shifted from the position of FIG. 4, corresponding to reverse rotation or braking, as described above, to the position of FIG. 3 corresponding to forward, high-speed rotation, the initial effect of the described system is to make thepiloted relief valve 35 function to limit the back pressure in pipe 34 for braking the reverse rotation of the centrifugal basket until the latter has been brought to rest, whereupon the normal flow is established through pipe 34 in the direction from relief valve 35 toward motor 42 for effecting the forward rotation of the basket.

The leakage characteristics of hydraulic motor 42 at low speed are such that the volumetric rate of delivery of hydraulic fluid to the motor has to be increased in order to maintain a constant speed when the load on the motor and hence the pressure of the hydraulic fluid supplied thereto are increased. Accordingly, if the hydraulic fluid is supplied to motor 42 at a constant rate of flow during reverse rotation of the motor, the speed of such reverse rotation would tend to decrease with increased load on the motor. In order to avoid such decreasing speed of reverse rotation, the hydraulic drive embodying the present invention may further include two adjustable flow control valves, which may be of the type available from Denison Engineering Division, American Brake Shoe Company, Columbus, Ohio, under the designation VlAAO23330, and which are identified by the reference numerals 61 and 62, respectively. The valves 61 and 62 are arranged in a circuit bypassing a check valve 63 interposed in pipe 50 and permitting flow through the latter only in the direction from motor 42 toward piloted relief valve 49. The bypass circuit includes a line 64 branching off from pipe 50 at a location between check valve 63 and relief valve 49 and leading to the inlet side of adjustable flow control valve 61, and a line 65 leading from the outlet of valve 61 back to pipe 50 at a location between check valve 63 and the connection -1 to the hose 52, so that, when the pilot line 53 of relief valve 49 is blocked and the output of pump 17 passes through piloted relief valve 49 in the direction toward motor 42, the flow of hydraulic fluid passes through adjustable control valve 61 which is set to determine the basic speed of reverse rotation. The flow of hydraulic fluid through the other flow control valve 62 is blocked unless the pressure in the line 50 between check valve 63 and the motor exceeds a predetermined value as a result of the imposition of a relatively high load on the motor 42, at which time flow also occurs through valve 62, thereby to increase the total rate of flow of hydraulic fluid for maintaining a substantially constant speed of rotation of motor 42. The flow of hydraulic fluid through valve 62 is controlled by a pilot operated sequence valve 66 which may be of the kind available from Denison Engineering Division, American Brake Shoe Compan Columbus, Ohio, under the desig nation KH-041-E06D, and which is interposed in a line 67 branching off from the line 64 and leading to the inlet of control valve 62, with the operation of the sequence valve being controlled by the pressure sensed by a pilot line 68 extending from pipe 50 between check valve 63 and motor 42. The output of flow control valve 62 is led back to pipe 50 by way of a line 69 which may be joined to the line 65 extending from the flow control valve 61.

As shown in FIG. 6, the arrangement of two flow control valves 61 and 62 and the sequence valve 66 in the hydraulic drive of FIG. 1 can be replaced by a single flow control valve 61 which is continuously adjusted by an actuating device 76 having a pressure sensing connection 77 to the pipe 65 at the downstream side of the remaining flow control valve 61 so that the pressure of the hydraulic fluid fed to motor 42 during reverse rotation operates device 76 to cause the latter to further open valve 61 in response to an increase in the sensed pressure, that is, in accordance with increasing loads on motor 42.

As shown in detail on FIG. 7, the actuating device 76 preferably includes a cylinder 78 secured to the housing of flow control valve 61, as by a bracket 79, and having a plug 80 screwed into one end for attachment to the pressure sensing connection 77. A tube 8 1 extends axially from plug 80 and has an axial bore 82. A sleeve 83 is axially slidable on tube 81 within cylinder 78 and has an external flange 84 at the end adjacent plug 80 with a radial pin 85 extending from flange 84 through an axial slot 86 in the top of cylinder 78. A hearing bushing 87 is screwed into the end of cylinder 78 remote from plug 80 and slidably receives the adjacent end of sleeve 83 which is closed by a screw plug 88. A restriction or metering rod 89 extends axially from screw plug 88 through bore 82 of tube 81 with a small radial clearance therebetween, and a helical compression spring 90 is disposed around sleeve 83 in cylinder 78 between plug 87 and flange 84 of sleeve 83 so as to urge the latter toward the right, as viewed in FIG. 7.

It will be apparent that the hydraulic fluid under pressure carried by connection 77 passes through the annular clearance between fixed tube 81 and restriction rod 89 and acts against the plug 88 to urge sleeve 83 to move toward the left, as viewed in FIG. 7, in opposition to the force of spring 90. Thus, when the pressure sensed by connection 77 increases in response to an increasing load on motor 42 during reverse rotation of the latter, the sleeve 83 and its radial pin 85 are displaced toward the left.

Further, as shown in FIG. 7, the flow control valve 61, which is commercially available from Denison Engineering Division, American Brake Shoe Company, Columbus, Ohio, under the designation VLAAO23330, as previously indicated, includes a rotatable knob assembly 91 for adjusting the rate of flow of hydraulic fluid through valve 61, and such knob assembly 91 is modified by providing two spaced apart, axially projecting pins 92 thereon between which the pin 85 of actuating device 76 engages so that movement of pin 85 along slot 86 causes angular displacement of knob assembly 9.1 to correspondingly adjust valve 61 for increasing the rate of flow of hydraulic fluid to motor 42 with increasing loads on the latter so as to compensate for the increased leakage through the motor and thereby maintain a constant speed of reverse rotation.

In order to provide indications of the pressures existing in the pipes 34 and 50 which feed fluid under pressure to the motor from the pumps 16 and 17, respectively, a pressure gauge 70 may be connected to a central port of valve housing 56 and, as shown in FIGS. 2, 3 and 4, the spool 58 of valve 55 is formed with a central land 71 which moves to one side or the other of the port communicating with gauge 70, so that the gauge indicates the pressure in pilot line 38 (FIG. 3) or in pilot line 53 (FIG. 4).

In order to prevent the imposition of an excessive back pressure on pump 17 and overspeeding of electric motor 11 in the event of a power failure during braking of high speed forward rotation of basket 45, a check valve 72 is interposed in pipe 48 between piloted relief valve 49 and the outlet of pump 17 and permits flow of fluid through pipe 48 only in the direction from the pump.

It will be seen that, if there is a power failure during high speed forward rotation of basket 45, the inertia of the rotating basket will cause motor 42 to act as a pump. However, the inlet 41 of motor 42 must be generously supplied with hydraulic fluid during such action as a pump in order to avoid cavitation and, for this purpose, a pipe 73 extends from the pipe 36 and opens into the pipe 34 at a location which is downstream wtih respect to the piloted relief valve 35, and a check valve 74 is interposed in the pipe 73 and permits flow through the latter only in the direction toward pipe 34. Thus, in the event of a power failure while control valve 55 is disposed for high speed forward rotation of basket 45, the hydraulic fluid returning from outlet 43 through hose 52, pipe Sil check valve 63, piloted relief valve 4d and pipe 54 passes through pipe 36 and the check valve 74 of pipe 73 to the pipe 34 in order to maintain an adequate'supply of hydraulic fluid at the inlet or suction side of motor 42 acting as a pump. Since there may be an excessive pressure drop across the check valve 74 at high rates of flow of hydraulic fluid therethrough, and this excessive pressure drop would have the tendency of permitting some of the returned hydraulic fluid passing through the pipe to flow back to the tank through the return pipe 37, and thereby result in an inadequate supply of oil to the inlet or suction side of motor 42 acting as a pump, there is further provided a spring loaded check valve 75 interposed in the return pipe 37 and creating a resistance to the return flow of fluid through pipe 37, thereby to overcome the flow resistance of the above described check valve 74.

As shown in FIG. 6, the above mentioned spring loaded check valve '75 may be replaced by a cooler 93 having a housing 94 with its inlet and outlet connected to return pipe 37 so that the return flow of fluid through pipe 37 passes through housing M. Cooler 93 further includes coils 95 of small diameter tubing disposed in housing 9 and creating a resistance to the return flow of fluid through pipe 37, for example, a pressure drop of p.s.i., which is sufficient to overcome a flow resistance of check valve 74, and water is circulated through coils 95 to cool the return flow of hydraulic fluid. Thus, cooler 93 performs the function of the check valve 75 which it replaces and also functions as an economical and effective fluid cooler.

In order to avoid cavitation in motor 42 in the event of a power failure during reverse rotation of basket 45, the

normal outlet 43 of motor 42 is then generously supplied with fluid by way of pipe 96 (FIG. 1) extending from pipe 54 and opening into pipe 50 at a location intermediate piloted relief valve 49 and check valve 63, and a check valve 97 is interposed in pipe 96 to permit flow therethrough only in the direction toward pipe 50.

From the above description of the centrifugal drive it embodying the present invention it will be apparent that hydraulic motor 4-2 can effect the high speed forward rotation of basket 45 during the normal spinning operation of the basket by disposing valve 55 in the position illustrated in FIG. 3. vi hen the solids in the basket charge have been dried to the desired extent, the control valve 55 can be moved manually or otherwise to the position of FIG. 4, at which time the piloted relief valve 35 is unloaded to drop the pressure in the pipe 34, while the piloted relief valve 49 closes and builds up to the pressure for which it is set, at which point valve 4% blows to the tank 12 the hydraulic fluid pumped by the pump 1'7 and by the hydraulic motor 42 acting as a pump. The pressure maintained in pipe 5!) by relief valve 49 is a back pressure on motor 42 causing the latter to exert a braking torque on the centrifugal basket. When the centrifugal basket 45 comes to rest, pump 17 continues to supply fluid under pressure to motor 42 by way of hose 52, pipe 5% and either the sequentially operated adjustable flow control valves 61 and 62 (FIG. 1) or the continuously adjusted flow control valve 6!. (FIG. 6). Further, as previously explained, the parallel connected adjustable flow control valves 61 and 62, when operated in sequence by the sequence valve as, or the single flow control valve 61 which is adjusted by actuating device '76, tend to maintain a constant speed of rotation of basket 35 in the reverse direction. Thus, the centrifugal 44 may be provided with a discharger of the kind disclosed in United States Letters Patent No. 2,667,974, which is more fully identified here inabove, and wherein the discharger shoe is continuously maintained within the basket 45 and extends generally in the direction of the normal high speed rotation of the basket so that it cannot dig into the wall of solids in the basket during such high speed rotation, but can dig into the wall of solids for effecting the discharge thereof through the bottom opening of the basket only during the controlled, low speed reverse rotation of the centrifugal basket.

Although the hydraulic drive 10 is shown with its motor 42 connected to the lower end of the basket shaft of a link suspended centrifugal, it is to be understood that hydraulic drives embodying this invention can be used with other types of centrifugals, for example, machines of the overhead suspended type or the like.

In the centrifugal drives 10 illustrated in FIGS. 1 and 6, separate pumps 16 and 17 provide the flows of hydraulic fluid under pressure employedfor high speed forward rotation of the basket 45 and for braking and slow speed reverse rotation of the basket, respectively, but a single pump can be employed to perform the functions of pumps in and 17. Thus, in the centrifugal drive illustrated diagrammatically in FIG. 8 and there generally identified by the reference numeral 100, the electric motor 111 has its shaft 113 connected by a coupling 114 to the shaft 119 of a variable volume, vane type pump 116 which may be of the kind previously described with reference to the pump 13?, and which draws fluid from the supply tank 112 through inlet pipe 132, while the outlet of pump 116 delivers hydraulic fluid under pressure to a pipe 133 which extends to a housing 156 of a distributing or control valve E55. Also extending from the valve housing 155 are a pipe 134 connected by a coupling 139 to a flexible pipe or hose 146 extending to the inlet 141 of a hydraulic motor M2 which may be the same as the motor 42 of FIG. 1 and is similarly adapted for direct coupling to a centrifugal basket (not shown), and a pipe 150 connected by a coupling 151 to a flexible hose or pipe 152 extending rorn the outlet 143 of motor 142. Further, a return pipe 137 extends from valve housing 156 back to the hydraulic fluid supply tank 112.

Valve 155 further includes a valve body or spool 158 which is axially slidable in housing 156 and has a rod 159 projecting from one end of the housing to permit the valve spool to be selectively disposed in the central position of FIG. 8, or in and toward the left, respectively, from the position of FIG. 3.

The spool 158 of control valve 155 may have two axially spaced apart annular recesses ing a narrow central land 2% from lands 201 and 2th, at the opposite ends of the spool, and such recesses and lands are disposed along the spool in relation to the positions where conduits 133, 134, 237 and 150 open into housing 156 so that, when spool 153 is in its centered position, as shown in FIG. 8, recesses 193 cation between all of the conduits 133, 134, 137 and 15%. Thus, when spool 153 is in its illustrated centered position, the output of pump 3.16 is dumped back to tank 112 through pipe 137, and hydraulic fiuid can circulate freely to and from motor E42 through pipes 134 and 159, so that the centrifugal basket either remains at rest, or coasts if the basket is in a state of rotation when the valve is moved to the position of FIG. 8.

When valve spool 15% is displaced toward the right from theposition shown in FIG. 8, pipes 133 and 1 34 communicate with each other across recess 1% and 137 communicate with each other across recess 199, so that the output of pump lid is fed by way of pipes 133 and 13d and hose to motor 142- to cause forward rotation of the latter, while the exhausted fluid is returned from the motor to tank 112 by way of hose 152 and pipes 15% and 137.

When valve spool 158 is displaced toward the left from the position illustrated in FIG. 8, pipes 133 and communicate with each other across the recess 199, and pipes 134 and 137 communicate with each other across the recess 138, so that the output of pump 116 is fed, by way of pipes 133 and 150 and hose 152 to motor 142 in order to cause reverse rotation of the latter, while the exhausted positions displaced toward the right I 298 and 3.99 separatand 199' establish communiand pipes 1 1 fluid is returned from the motor to tank 112 by way of hose 141 and pipes 134 and 137.

As shown in FIG. 8, the hydraulic centrifugal drive 1019 further includes a pressure relief valve 135 interposed in pipe 134 for limiting the maximum pressure in the latter, and being effective to dump hydraulic fluid to the return pipe 137 by way of a branch pipe 136 whenever the pressure in pipe 134 exceeds the value for which the pressure relief valve is set. The pipe 151 also has a pressure relief valve 149 interposed therein for limiting the maximum pressure of the hydraulic fluid in that pipe, and valve 149 is eflective to dump hydraulic fluid from pipe 150 into pipe 134 by way of a branch pipe 132 whenever the pressure in pipe 151) exceeds the predetermined value for which valve 149 has been set.

Hydraulic fluid under pressure is supplied to motor 142 through pipe 134 to effect forward rotation, and through pipe 156 to effect reverse rotation, and the pressure relief valves 135 and 149 are respectively set to permit a higher pressure in pipe 151 than in pipe 134, so that a greater braking torque will be available to bring the centrifugal basket to rest or to a desired relatively low speed of rotation after forward rotation of the basket at high speed.

In order to provide the small rate of flow of hydraulic fluid under pressure to motor 142 necessary for eflecting the slow reverse rotation of the latter, pipes 164 and 165 by-pass a portion of pipe 150 located between pressure relief valve 149 and hose 152, and a check valve 163 is interposed in the by-passed portion of pipe 151? and permits flow therethrough only in the direction from the motor back to the valve 155, whereas flow toward motor '142 can only occur through the bypass pipes. The bypass pipes 164 and 165 have an adjustable flow control valve 161 interposed therebetween in order to provide the necessary throttling of the flow for the desired slow reverse rotation of motor 142.

Since motor 142 has increasing leakage with increasing loads on motor 142 during the slow reverse rotation of the latter, it is necessary to increase the rate of flow of hydraulic fluid under pressure through hose 152 to motor 142 in order to maintain a substantially constant speed of slow reverse rotation of motor 142 with increasing loads on the latter. For this purpose, the hydraulic centrifugal drive 100 of FIG. 8 includes a single adjustable flow control valve 161 which, as in the modification of FIG. 6, is operated by an actuating device 176 having a pressure sensing connection 177 to the pipe 165 at the downstream side of flow control valve 161, so that the pressure of the hydraulic fluid fed to motor 142 during reverse rotation acts in actuating device 176 to further open flow control valve 161 in response to an increasing pressure, that is, in accordance with increasing loads on motor 142.

Hydraulic drive 101) further includes a check valve 187 interposed in pipe 133 to permit flow through the latter only in the direction from pump 116 to valve 155, and thereby protect pump 116 from back pressures that are higher than its rated pressure, for example, the braking or back pressure occurring in pipe 133 when valve 155 is shifted to the position for reverse rotation or braking of motor 142 while the motor and the basket driven thereby are undergoing forward rotation.

A check valve 188 is interposed in the pipe 162 to permit flow through the latter only in the direction from relief valve 14-9 to pipe 134, and a spring loaded check valve 175 is interposed in the return pipe 137 to permit flow through the latter in the direction toward tank 112.

When valve 155 is shifted to the braking and reverse rotation position while the basket driven by motor 142 is undergoing high speed rotation in the forward direction, motor '142 acts as a pump which builds up pressure through check valve 163 against relief valve 149', and the latter limits this back pressure causing the motor to exert a braking torque. An excess back pressure of hydraulic fluid is dumped by valve 149 through check valve 188 to pipe 134 to maintain an adequate supply of hydraulic fluid at the inlet 141 of motor 142, thereby to prevent cavitation in the motor. The spring loaded check valve 175 in return pipe 137 establishes a suflicient resistance to the flow of hydraulic fluid through the return pipe back to the tank to overcome the flow resistance of check valve 188 causing a pressure drop across the latter, and thereby ensures that the hydraulic fluid passing through check valve 183 will travel along pipe 134 in the direction toward motor 142, rather than in the opposite direction through. pipe 134 and return pipe 137 to the tank.

Although the arrangement illustrated in FIG. 8 has the advantage over the arrangement shown in FIG. 1 of eliminating the auxiliary pump 17 of the latter, this advantage is obtained at the expense of providing a closed circuit for the hydraulic fluid flowing through motor 142 during braking of high speed forward rotation, so that difficulties may be experienced in the dissipation of heat from the limited volume of hydraulic fluid circulating rapidly through the closed braking circuit and thus having an insufficient time for adequate cooling by radiation during each passage through the closed braking circuit. Further, when two pumps are provided, as in the embodiment of FIG. 1, the auxiliary pump 17 may be selected so as to provide a substantially higher pressure of hydraulic fluid than the rated pressure of the main, variable volume pump 16, thereby to provide a maximum torque for relatively slow reverse rotation of the centrifugal basket, for example, during discharging of the latter.

Referring to FIGS. 1, 6 and 8, it will be seen that the hydraulic drives embodying this invention may be further provided with a difl'erential pressure responsive switch 263, for example, of the type that is commercially available under the designation Barksdale No. 532-9, which is operated by a difference between the pressures at the opposite sides of the check valve 63 or 163, as sensed in pipes 294 and 295. The switch 203 controls an electrical circuit 206 that includes a battery or other electrical source 2117 and a signal 208, for example, a lamp, which is energized only when a predetermined pressure drop is sensed by switch 263. During forward rotation of motor 42 or 142, the return flow through pipe 5% or 150 passes through check valve 63 or 163 so that the differential pressure or pressure drop necessary for operating switch 293 is not then available. However, during reverse rotation of the motor, check valve 63 or 163 blocks the direct flow of hydraulic fluid under pressure through the pipe or 150 and causes the flow of hydraulic fluid under pressure to be diverted through the bypass containing the two flow control valves 61 and 62 (FIG. 1) or the single continuously adjusted flow control valve 61 or 161 (FIGS. 6 and 8), and the flow control valve or valves produce a pressure drop of the order necessary for operating the differential pressure responsive switch 263 when the motor 42 or 142 is turning in the reverse direction at a predetermined slow speed which is safe for discharging, thereby energizing the signal 263 to indicate that conditions safe for discharging have been attained.

Referring now to FIG. 9 which illustrates a modification of a portion of the hydraulic drive shown in FIG. 8, it is to be understood that the remainder of the drive may be the same as that in FIG. 8. In the modification of FIG. 9, the distributing or control valve a has its spool 158a which is movable within the valve housing 156a formed with a middle land 266a which is not centered between the end lands 201a and 262a, so that the annular recess 193a has a greater axial length than the annular recess 199a. By reason of the above, the spool 1585:, when in its central position shown in FIG. 9, establishes communication between the conduit 133 carrying hydraulic fluid from the outlet of the single pump and the conduits 134 and 137, by way of annular recess 198a, while the lands 266a and 2412 close otf the communications between the conduit 156 and the conduits 133 and 137, respectively. When valve spool 153a is shifted toward the right from the position of FIG. 9, conduit 150 is communicated with return conduit 137 by way of annular recess 199a, while annular recess 198a establishes communication between conduits 133 and 134 and land 201a blocks the port at the a-diacent end of housing 155a opening into conduit 137. On the other hand, when valve spool 158a is shifted toward the left from the position shown in FIG. 9, annular recess 19% establishes communication between conduits 133 and 154 and annular recess 153a establishes communication between conduits 1 34 and 137.

Further, the modified hydraulic drive illustrated in FIG. 9 has conduits 136 and 154 extending from the pressure relief valves 135 and 149 to the return conduit 137 and through which the respective pressure relief valves dump hydraulic fluid back to the tank or reservoir when the pressures acting on the relief valves exceed adjustably predetermined values. in order to prevent cavitation in the motor 142 during operation of the latter as a pump upon continued rotation of the motor in either the forward or reverse direction at a time when the control valve 155a is positioned for reverse or forward rotation, respectively, the modified drive of FIG. 9 further includes check valves 174- and 137 which correspond to the check valves 74 and 97, respectively, of the drive shown in PEG. 1. Check valves 174 and 197 are respectively interposed in conduits 173 and 15 6 which are branches of a conduit extending from the return conduit 154 and which open into the conduits 134 and 1511, respectively, at a location between pressure relief valve 135 and the motor and at a location between the pressure relief valve 149 and the bypass conduit 164 extending from conduit 150, respectively.

The modification of FIG. 9 further includes a cooling device 193 which replaces the check valve 175 of FIG. 8 and which corresponds to the cooling device 93 of the modification illustrated in FIG. 6. The cooling device 193 has a cooling coil 135 interposed in its housing 194 so as to provide a suitable restriction in the return flow of hydraulic fluid to the storage tank by way of the return conduit 137.

The modified hydraulic drive illustrated in FIG. 9 operates as follows:

When valve spool 158:; is displaced toward the right from the central position illustrated in FIG. 9, hydraulic fluid under pressure passes from the pump through conduit 133 and conduit 134 to the motor of the centrifugal, while the discharge from the motor passes through conduit 150 into conduit 137 for return to the tank so that the motor is driven at a relatively high speed in the forward direction. If valve spool 158:: is returned to its illustrated central position while the motor is still being rotated in the forward direction by the inertia of the basket attached thereto, communication between conduits 151 and 137 by way of valve 155a is blocked, thereby building up the pressure acting on relief valve 149 which limits the pressure for obtaining a predetermined braking torque, while the excess pressure of hydraulic fluid is dumped back to the tank through conduits 154-, 13s and 137. During such braking of the forward rotation of the motor, the hydraulic fluid is cooled by passage through the cooling device 193 during its return to the storage tank. Further, by reason of the fact that conduits 133, 13 1- and 137 are all communicated with each other through valve 155a when the latter is in the position of FIG. 9, fresh hydraulic fluid is continuously added to the braking circuit from conduit 133- to conduit 134, but such added fluid is not under pressure as a result of the communication of conduits 133 and 134 with return conduit 137. Thus, the problem of excessive heating of the hydraulic fluid circulating within a closed braking loop or circuit as mentioned above in connection with the description of the hydraulic drive of FIG. 8 is substantially avoided.

During braking of the forward rotion of the motor, the check valve 174 permits additional hydraulic fluid to be drawn into conduit 134 from conduit 154 so as to ensure an adequate supply of hydraulic fluid to the motor acting as a pump for avoiding cavitation in the latter.

If spool 158a remains in the central position illustrated in FIG. 9 after forward rotation of the motor has been halted in the manner indicated above, the motor will remain at rest by reason of the fact that hydraulic fluid under pressure carried from the pump by conduit 133 is dumped back to the storage tank by way of conduit 137. Further, if valve spool 15% is disposed in the central position of FIG. 9 during rotation of the motor in the reverse direction, the fluid discharged from, the motor through conduit 134 can pass without resistance through valve 155a into return pipe or conduit 137, while a free circulation of fluid to the motor occurs through conduits 137, 136, 154, 196 and thereby permitting the motor to coast in the reverse direction. When valve spool 158a is displaced toward the left from the position illustrated in FIG. 9, fluid under pressure passes from conduit 133 through the valve into conduit 150- for supply to the motor by way of the continuously adjustable flow control valve 161 (FIG. 8), while the discharge from the motor flows through conduit 134 and valve a into the return conduit 137.

Referring to FIG. 10, it will be seen that the further modification of the hydraulic drive of FIG. 8 which is there illustrated employs a distributing or control valve 155 having the same construction as the valve 155 of FIG. 8, but simplifies the drive by using a single pressure relief valve 235 which is interposed in conduit 133 extending from the single pump to the control or distributing valve and being operative to dump hydraulic flu d from conduit 133 through a conduit 236 to the return conduit 137 when the pressure in conduit 133- exceeds an adjustably predetermined value. Further, in the drive of FIG. 10, the check valves 174 and 197, which are provided to prevent cavitation during a power failure while the motor is rotating in the forward or reverse directions, respectively, are interposed in conduits which branch off from a common connection to the conduit 236 and open into the conduits 134 and 150, respectively.

The modified drive of FIG. 10 operates as follows:

The central position of spool 15% of vlave 155 establishes communication between all of the conduits 133, 134, 137 and 150 so that, if the motor is at rest, it will continue in that condition, or if the motor is rotating in the forward or reverse direction, it will continue to coast in that same direction.

When spool 158 is displaced toward the right from the central position of FIG. 10, conduits 133 and 134- communicate with each other through valve 155 which simultaneously establishes communication between conduits 150 and 137 so that hydraulic fluid under pressure is supcharged fluid is carried away from the motor through conduit 15%, thereby effecting forward rotation of the motor. If the motor is rotating in the reverse direction when the valve. 155 is positioned for forward rotation, the

motor acts as a pump backing up a pressure of hydraulic fluid through conduits 134 and 133 to the pressure relief valve 235, and the latter dumps the excess pressure of fluid through conduits 236 and 137 back to the storage tank or reservoir, thereby determining the braking torque which is applied for halting the reverse rotation. At the same time, check valve 197 permits hydraulic fluid to flow from conduit 236 into conduit 150 in order to ensure an adequate supply of hydraulic fluid to the motor which then acts as a pump during braking of the reverse rotation.

When a spool 158 is displaced toward the left from i the central position of FIG. 10, communication is established between conduits 134- and 137 and between conduits 133 and 1511, thereby to supply fluid under pressure 1 to the motor in the direction for effecting reverse rotation thereof. If the motor is undergoing high speed rotation in the forward direction at the time when valve spool 153 is disposed in the position for reverse rotation, the motor acts as a pump and backs up pressure through conduit 15%) and conduit 133 so that relief valve 235 once again limits the maximum pressure, and thereby determines the braking torque available for halting forward rotation of the motor. At the same time, check valve 174 permits fluid to flow from conduit 236 into conduit 134 for ensuring an adequate supply of fluid to the motor acting as a pump during braking of the forward rotation.

Referring now to FIG. 11, it will be seen that the hydraulic drive there illustrated is a further modification of the drive of FIG. 1 including the features previously described with reference to FIG. 6, and with the drive being arranged so that the outputs of pumps 16 and 17 can be used in parallel to provide an increased rate of flow of hydraulic fluid to the motor 42 during rotation of the latter in the forward direction. Such increased rate of flow to the motor 42 can be used for achieving higher rotational speeds of the motor, or for supplying hydraulic fluid under pressure to larger motors which develop increased torque for faster acceleration of the driven basket or for easier discharging of solids from the latter.

In the hydraulic drive illustrated in FIG. 11, and there generally identified by the reference numeral 360, the various parts corresponding to those previously described with reference to FIGS. 1 and 6 are identified by the same numerals. The drive 306 includes a conduit 301 having a check valve 72 and a pressure gauge 76 interposed therein and extending from the outlet of auxiliary pump 17 to the central port of the distributing or control valve 55. A conduit 302 extends from the outlet of the main variable delivery pump 16 to the piloted relief valve 35 and has a check valve 303 interposed therein to permit flow through conduit 302 only in the direction from pump 16 toward piloted relief valve 35. As in FIG. 1, a conduit 34 extends from piloted relief valve 35 for connection to the normal inlet 41 of the hydraulic, positive displacement motor 42, and a pipe 36 is also connected to piloted relief valve 35 and opens into a return pipe 37 extending back to tank 12 and in which a cooler 93 is interposed for the purposes previously described in detail with reference to FIG. 6.

A pipe 304 extends from one of the delivery ports of valve housing 56 and connects to the conduit 302, with a check valve 365 being interposed in pipe 304 to permit flow through the latter only in the direction from valve 55 toward piloted relief valve 35. The pilot line 38 for piloted relief valve 35 extends from the latter to pipe 304 at a location along the latter intermediate distributing valve 55 and check valve 305.

The other delivery port of valve housing 56 is connected by a pipe 396 to the piloted relief valve 49 and a check valve 3t'l7 is interposed in pipe 306 to permit flow through the latter only in the direction toward the related piloted relief valve. The pilot line 53 of relief valve 49 extends from the latter back to the pipe 306 at a location along the latter between check valve 307 and distributing valve 55. A conduit 50 extends from piloted relief valve 49 for connection to the normal outlet 43 of motor 42, and has the check valve 63 interposed therein to permit flow therethrough only in the direction from the motor towards relief valve 49, and, as in the modification of FIG. 6, check valve 63 is by-passed by pipes 64 and 65 having the flow control valve 61 interposed therebetween and being continuously adjusted by the actuating device 76 which responds to the pressure sensed in conduit 50 through a sensing connection 77.

Hydraulic fluid dumped by the piloted relief valve 49 is led from the latter through a pipe 54 to the return conduit 37. As in the drive of FIG. 1, the drive shown in FIG. 11 further includes check valves 74 and 97 interposed in conduits 73 and 96 which extend between the return conduit 37 and the conduits 34 and 56, respec- 16 tively, in order to ensure an adequate supply of hydraulic fluid at the normal inlet 41 and the normal outlet 43, respectively, of motor 42 either during continued forward or reverse rotation of the motor following a power failure, or during braking of the forward or reverse rotation of the motor by positioning of spool 58 of distributing valve 55 in the position for reverse rotation or in the position for forward rotation, respectively.

The above described hydraulic drive illustrated in FIG. 11 operates as follows:

When spool 58 of control or distributing valve 55 is in its illustrated central position, the pipes or conduits 3G1, 304 and 306 are all in communication with the drain conduit 57 extending from the valve housing 56 to the return conduit 37 so that the output of pump 17 is returned to tank 12 and the pilot lines 38 and 53 of piloted relief valves 35 and 49 are both vented to the tank. Thus, the unloaded piloted relief valve 35 dumps the output of main pump v16 back to the tank 12 by way of pipes 36 and 37 and the motor 42 remains at rest if it is initially in that condition. Since piloted relief valve 49 is also unloaded, the motor 42 will coast in either the forward or reverse direction upon disposition of valve spool 58 in its illustrated central position.

When spool 58 is displaced toward the right from the central position illustrated in FIG. 11, conduit 331 is placed in communication with pipe 304 so as to feed the output of auxiliary pump 17 through pipe 304 which opens into conduit 302 so that the combined flows of pumps 16 and 17 then pass through conduit 34 to the normal inlet 41 of motor 42. When pipe 394 is connected to conduit 301, as previously described, piloted relief valve 35 is loaded through pilot line 38, and thereby establishes a predetermined maximum pressure for the hydraulic fluid in conduit 34. The displacement of spool 58 toward the right also establishes communication between pipe 306 and the return or drain conduit 57 so that pilot line 53 of relief valve 49 is vented to the tank, whereby the hydraulic fluid discharged from the normal outlet 43 of motor 42 is carried by conduit 50 through check valve 63 to relief valve 49 and is dumped by the latter through conduit 54 and return conduit 37 back to tank 12. Accordingly, motor 42 is then rotated in the forward direction by the combined flows of pumps 16 and 17.

If spool 58 is disposed in the above described position for forward rotation of pump 42 at a time when the latter is rotating in the reverse direction, so that motor 42 then operates as a pump, the loaded piloted relief valve 35 determines the maximum pressure permitted in conduit 34, and thereby establishes the braking torque for halting rotation in the reverse direction, while fluid is supplied by way of conduit 50 to the normal outlet 43 through the loaded relief valve 35 and check valve 97 in order to avoid cavitation in motor 42. Similarly, in the event of a power failure while the motor is rotating in the reverse direction, fluid is supplied by way of conduit 50 to the normal motor outlet 43 through the unloaded relief valve 35 and check valve 97.

When spool 58 is displaced toward the left from the central position of FIG. 1'1, communication is established between conduit 391 and pipe 306, thereby loading piloted relief valve 49 by way of its pilot line 53 and feeding the flow from pump 17 through the adjustable flow control valve 61 to the normal outlet 43 of motor 42. At the same time, pipe 304 is vented to the tank thereby unloading piloted relief valve 35 so that the discharge from motor 42 during reverse rotation of the latter is dumped by valve 35 through conduits 36 and 37 back to the tank 12, and the output of the main variable delivery pump 16 is also dumped through the unloaded relief valve 35 back to the tank.

If spool 58 of valve 55 is placed in its position for reverse rotation, as described above, at a time when the motor 42 is rotating in the forward direction, whereby 17 the motor acts as a pump, the loaded piloted relief valve 49 establishes the maximum pressure in conduit 50, and thereby determines the braking torque, while fluid is supplied to the normal inlet 41 of the motor through the unloaded piloted relief valve 35 and the check valve 74 in order to prevent cavitation in the motor by reason of an inadequate supply of fluid. In the event of a power failure while the motor is rotating in the forward direction, fluid pumped by the motor 42 acting as a pump spills over the unloaded relief valve 49 and passes via conduits 54 37 and 73 and check valve 74 into conduit 34 from where it is supplied to the inlet 41 of the motor to prevent cavitation therein.

The hydraulic drive of FIG. ll further preferably includes unloading valves 3438 and 3% which are respectively interposed in the conduits 361 and 392 respectively extending from the outlets of pumps 17 and 16, and which are operative to unload one of the pumps until the full delivery or output of the other pump has been utilized by the hydraulic motor 42. Valves capable of performing the above mentioned operations of valves 30% and 309 are commercially available from Denison Engineering Division, American Brake Shoe Company, Columbus, Ohio, under the designations RJGdl-E06A and RJ101E06A, respectively. The unloading valves 3638 and 3&9 automatically dump back to the tank 12 the unutilized outputs of the respective pumps, thereby reducing the peak load on the electric motor driving the pumps and also reducing the heating of the circulated hydraulic fluid. If the unloading valves 3% and 309 are not used in the drive of FIG. 11, the variable delivery main pump 16 will automatically adjust back to Zero delivery, and the excess output of the fixed volume auxiliary pump will be dumped back to the tank by piloted relief valve 35 until the motor has accelerated the centrifugal basket up to about 20% of its rated forward speed.

It will be apparent from the above that hydraulic drives embodying the present invention are capable of driving a centrifugal basket with a high speed in the forward direction reached by either a constant horse-power or constant torque acceleration, which is determined by selection of the governor spring 27 of pump 16, and further that the drives embodying this invention are capable of driving the basket at an adjusted relatively low speed in the reverse direction, which low speed is continuously maintained even during a varying load on the basket, for example, during discharging of solids therefrom. Further, the described hydraulic drives provide exclusively hydraulic braking of either forward or reverse rotation of the motor down to rest, and also protect the motor against any damage due to cavitation either during braking or in the event of a power failure.

Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein without departing from the scope or spirit of the invention, except as defined in the appended claims.

What is claimed is:

l. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a load such as a centrifugal basket for driving the latter, first and second conduit means connected to said motor and forming a circuit through which hydraulic fluid can travel to and from said motor in opposite directions for effecting forward and reverse rotation of said motor, a prime mover, pumping means driven by said prime mover to deliver hydraulic fluid under pressure to said circuit, first and second pressure relief means interposed in said first and second conduit means, respectively, between said pumping means and said motor and operative to limit the pressures motor in the direction corresponding to reverse rotation of hydraulic fluid in each of said conduit means to a predetermined value by dumping fluid therefrom, means operable to interrupt the supply of fluid to said motor through one of said conduit means while the motor is rotating in the direction efiected by travel of fluid thereto through that conduit means and simultaneously to increase the pressure in said other conduit means above said predetermined value, and means operative upon the interruption of the supply of fluid through said one conduit means to supply to that conduit means and thence to said motor an amount of the fluid being dumped by the pressure relief means in said other conduit means suiiicient to prevent cavitation in said motor as it continues to rotate in the last named direction due to the momentum of the load on said motor.

2. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, conduit means connected to said motor and forming a circuit through which hydraulic fluid can circulate to and from said motor in opposite directions for effecting forward and reverse rotation of said motor, a prime mover, pumping means driven by said prime mover and delivering hydraulic fluid under pressure to said circuit, control means selectively determining the direction of circulation of hydraulic fluid through said circuit from said pumping means, means restricting the rate of flow of hydraulic fluid through said circuit to the motor in the direction corresponding to reverse rotation of the motor, thereby to cause relatively slow reverse rotation, and means operative in response to a predetermined pressure drop across said restricting means correspending to a predetermined speed of reverse rotation of said motor to generate a signal indicating that that predetermined speed has been attained.

3. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, conduit means connected to said motor and forming a circuit through which hydraulic fluid can circulate to and from said motor in opposite directions for effecting forward and reverse rotation of said motor, a prime mover, pumping means driven by said prime mover and delivering hydraulic fluid under pressure to said circuit, control means selectively determining the direction of circulation of hydraulic fluid through said circuit from said pumping means, means restricting the rate of flow of hydraulic fluid through said circuit to the motor in the direction corresponding to reverse rotation of the motor, thereby to cause relatively slow reverse rotation, and means operative to increase the restricted rate of flow of the hydraulic fluid upon increased loading of said motor, thereby to compensate for increased leakage in the motor and tend to maintain a substantially constant speed of reverse rotation.

4. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, conduit means connected to said motor and forming a circuit through which hydraulic fluid can circulate to and from said motor in opposite directions for effecting forward and reverse rotation of said motor, a prime mover, pumping means driven by said prime mover and delivering hydraulic fluid under pressure to said circuit, control means selectively determining the direction of circulation of hydraulic fluid through said circuit from said pumping means, means restricting the rate of flow of hydraulic fluid through. said circuit to the of the motor, thereby to cause relatively slow reverse rotation, and means responding to the pressure in said circuit between said motor and said restricting means to increase said rate of flow with increasing pressure, thereby to tend to maintain a constant speed of reverse rota- 13 tion as leakage in said motor increases With increasing load on the motor.

5. A hydraulic drive for centrifugals as in claim 4; wherein said responding means includes a servo-motor connected to said adjustable restricting means and spring urged in the direction for decreasing said rate of flow, and means transmitting said pressure in the circuit to said servo-motor to act in the =latter in the direction for increasing said rate of flow.

6. A hydraulic drive 'for centrifu-gals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, conduit means connected to said motor and forming a circuit through which hydraulic fluid can circulate to and from said motor in opposite directions 'for effecting forward and reverse rotation of said motor, a prime mover, pumping means driven by said prime mover and delivering hydraulic fluid under pressure to said circuit, control means selectively determining the direction of circulation of hydraulic fluid through said circuit from said pumping means, a plurality of adjustable flow control valves connected in parallel in said circuit to restrict the rate of flow of hydraulic fluid through said circuit to said motor in the direction corresponding to reverse rotation of the motor, thereby to cause relatively slow reverse rotation of the motor, and means sequentially including said flow control valves in said circuit in accordance with increasing load on said motor, thereby to increase said rate of flow and tend to maintain a desired speed of reverse rotation as the leakage in said motor increases with increasing load.

7. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, conduit means connected to said motor and ctorming a circuit through which hydraulic fluid can circulate to and from said motor in opposite directions for efiecting forward and reverse rotation of said motor, a prime mover, pumping means driven by said prime mover and delivering hydraulic fluid under pressure to said circuit, control means selectively determining the direction of circulation of hydraulic fluid through said circuit from said pumping means, a plurality of adjustable flow control valves connected in parallel in said circuit to restrict the rate of flow of hydraulic fluid to said motor in the direction corresponding to reverse rotation of the motor, thereby to cause relatively slow reverse rotation of the motor, and normally closed sequence valve means connected in series with one of said flow control valves to prevent the flow of hydraulic fluid through said one flow control valve until the pressure of the flow of hydraulic fluid to the motor exceeds a predetermined value, whereupon said sequence valve means opens to include said one control valve in said circuit and increase said rate of flow for compensating the increased leakage in said motor resulting from increased loading thereof.

8. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, conduit means connected to said motor and forming a circuit through which hydraulic fluid can circulate to and from said motor in opposite directions for eflecting forward and reverse rotation of said motor, a prime mover, pumping means driven by said prime mover and delivering hydraulic fluid under pressure to said circuit, control means selectively determining the direction of circulation of hydraulic fluid through said circuit from said pumping means, check valve means in a portion of said circuit through which hydraulic fluid flows in the direction from said motor during forward rotation of the latter and permitting flow through said check valve means only in said direction from the motor, by-pass conduit means extending from said portion of the circuit around said check valve means, flow restricting means in said bypass conduit means to provide a restricted rate of flow therethrough -to the motor in the direction corresponding to reverse rotation of said motor, thereby to ensure relatively slow reverse rotation and means operative in response to variations in the load on said motor to vary the rate of flow through said restricting means in compensation for variations in the leakage in the motor resulting from said load variations and thereby maintain the speed of reverse rotation substantially constant.

9. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, conduit means connected to said motor and forming a circuit through which hydraulic fluid can circulate to and from said motor in opposite direction for effecting forward and reverse rotation of said motor, a prime mover, pumping means driven by said prime mover and delivering hydraulic fluid under pressure to said circuit, control means selectively determining the direction of circulation of hydraulic fluid through said circuit from said pumping means, pressure relief means interposed in said circuit between said pumping means and said motor to limit the pressures of hydraulic fluid in said circuit acting on said motor, means restricting the rate of flow of hydraulic fluid through said circuit to the motor in the direction for effecting reverse rotation of the motor, thereby to cause relatively slow reverse rotation and means operative in response to variations in the load on said motor to vary the rate of flow through said restricting means in compensation for variations in the leakage in the motor resulting from said load variations and thereby maintain the speed of reverse rotation substantially constant.

10. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, conduit means connected to said motor and forming a circuit through which hydraulic fluid can circulate to and from said motor in opposite directions for effecting forward and reverse rotation of said motor, a prime mover, pumping means driven by said prime mover and delivering hydraulic fluid under pressure to said circuit, control means selectively determining the direction of circulation of hydraulic fluid through said circuit from said pumping means, pressure relief means interposed in said circuit between said pumping means and said motor to limit the pressures of hydraulic fluid in said circuit acting on said motor, check valve means in a portion of said circuit through which the hydraulic fluid flows in the direction from the motor during forward rotation of the latter and permitting free flow through said portion of the circuit only in said direction from the motor, by-pass conduit means extending from said portion of the circuit around said check valve means, flow restricting means in said by-pass conduit means to provide a restricted rate of flow therethrough to the motor in the direction for reverse rotation of the latter, thereby to ensure relatively slow reverse rotation, and means operative in response to variations in the load on said motor to vary the rate of flow through said restricting means in compensation for variations in the leakage in the motor resulting from said load variations and thereby maintain the speed of reverse rotation substantially constant.

11. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, a prime mover, variable volume pumping means driven by said prime mover, relatively high pressure pumping means driven by said prime mover, a tank for containing hydraulic fluid to be delivered under pressure by each of said pumping means, first and second conduit means extending between said variable volume pumping means and said motor and between said high pressure pumping means and said motor, respectively, and alternately carrying fluid under pressure to and from said motor for effecting forward and reverse rotation of said motor, piloted pressure relief valve means in each of said conduit means having a loaded condition, in which said valve means determines the maximum pressure in the related conduit means, and an unloaded condition, in which the valve means dumps the output of the related pumping means back to said tank, and control valve means operative selectively to unload one of said pressure relief valve means while loading the other of said pressure relief valve means, and to unload said other pressure relief valve means while loading said one pressure relief valve means.

12. A hydraulic drive for centrifugals as in claim 11; further comprising return pipe means extending from said pressure relief valve means to said tank for returning the hydraulic fluid dumped by said pressure relief valve means, and a connecting pipe means extending from saidreturn pipe means to said first conduit means at a location along the latter between the related pressure relief valve means and said motor, and a check valve in said connecting pipe means permitting flow through the latter in the direction toward said first conduit means, so that, in the event of a failure of said prime mover While said motor is rotating in the forward direction, said first conduit means can draw fluid from said return pipe means to ensure that a sufiicient supply of fluid is available to the motor for preventing cavitation.

13. A hydraulic drive for centrifugals as in claim 12; further comprising a spring loaded check valve in sai return pipe means permitting flow through the latter in the direction toward said tank and imposing a resistance to such flow toward the tank which is greater than the flow resistance of said check valve in said connecting pipe means.

14. A hydraulic drive for centrifugals as in claim 12; further comprising a cooling device including a housing interposed in said return pipe means, and a cooling coil in said housing adapted to have a coolant circulated the-rethrough for cooling the liow of hydraulic fiuid passing through said return pipe means and said housing, said cooling coil interposing a resistance to the fiow through said housing which is greater than the resistance of said check valve in said connecting pipe means.

15. .A hydraulic drive for centrifugals as in claim 12; further comprising additional connecting pipe means extending irom said return pipe means to said second conduit means at a location along the latter between the related pressure relief valve means and said motor and having a check valve interposed therein to permit flow through said additional connecting pipe means only in the direction toward said second conduit means, so that, in the event of a failure of said prime mover while said motor is rotating in the reverse direction, said second conduit means can draw fluid from said return pipe means to ensure that an adequate supply of fluid is available to the motor for preventing cavitation.

16. A hydraulic drive for centrifugals as in claim 11; wherein said second conduit means has a check valve interposed therein to permit flow therethrough only in the direction from said motor to the pressure relief valve means in said second conduit means; and further comprising bypass conduit means connected to said second conduit means around said check valve in the latter so that fluid under pressure can flow through said bypass conduit means in the direction toward said motor for effecting reverse rotation of the latter, and flow restricting means interposed in said bypass conduit means to limit the rate of flow therethrough and thereby provide a relatively slow speed of reverse rotation.

17. A hydraulic drive for centrifugals as in claim 16; wherein said flow restricting means includes a plurality of adjustable flow control valves connected in parallel in said bypass conduit means, and normally closed sequence valve means connected in series with one of said flow control valves to prevent the flow of hydraulic fluid through said one flow control valve, said sequence valve means opening in response to the exceeding of a predetermined pressure in said second conduit means between said motor and check valve, thereby to permit flow through said one flow control valve for increasing the rate of flow of fluid through said bypass conduit means to said motor in order to compensate for increased leakage in the motor upon increased loading of the latter.

18. A hydraulic drive for centrifugals as in claim 16; wherein said flow restricting means includes an adjustable fiow control valve, and actuating means for said flow control valve responsive to the pressure in said second conduit means between said check valve in the latter and said motor to decrease the flow restricting effect of said flow control valve upon increases in said pressure, thereby to compensate for the increased leakage in the motor resulting from increased loads for maintaining a substantially constant speed of reverse rotation.

. 19. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, a prime mover, variable volume pumping means driven by said prime mover, a tank containing hydraulic fluid to be delivered under pressure by said pumping means, control valve means connected to said pumping means to receive the fluid under pressure delivered by the latter, first and second conduit means extending from said control valve means to said motor and alternately carrying hydraulic fluid to and from said motor for effecting forward and reverse rotation of the latter, return pipe means extending from said control valve means to said tank, said control valve means having a forward drive position in which said pumping means and first conduit means are connected while said second conduit means communicates with said return pipe means, a braking and reverse drive position in which said pumping means is connected to said second conduit means while said first conduit means communicates with said return pipe means and a rest and coasting position in which said pumping means is connected to said return pipe means while said first and second conduit means communicate with each other and means in said second conduit means operative in response to fluid pressure in that conduit means in excess of a predetermined value to dump from that conduit means to said first conduit means fluid in an amount sufficient to limit'the pressure in said second conduit to said valve, so that when said control valve means is moved to said braking and reverse drive position while said motor is rotating in the forward direction said pressure responsive means determines the back pressure in said second conduit means acting on said motor to produce a braking torque and fluid is dumped by said pressure responsive means to'said first conduit means whence it is supplied to said motor to prevent cavitation therein.

20. A hydraulic drive for centrifugals as in claim 19; further comprising a first pressure relief valve in said first conduit means, saidpressure responsive means including a second pressure relief valve in said second conduit means.

21. A hydraulic drive for centrifugals as in claim 20; said pressure responsive means further including a branch pipe extending from said second pressure relief valve to said first conduit means at a. location along the latter between said first pressure relief valve and said motor to receive hydraulic fluid dumped by said second pressure relief valve when the pressure in said second conduit means becomes excessive, and a check valve in said branch pipe permitting flow through the latter only in the direction toward said first conduit means, so that, when said control valve means is moved to said braking and reverse drive position while said motor is rotating-in the forward direction, said second pressure relief valve deter- 23 mines the back pressure in said second conduit means acting on said motor to produce a bnaking torque, and fluid is supplied to said first conduit means and said motor from said second pressure relief valve by way of said branch pipe.

22. A hydraulic drive for centrifugals as in claim 21; further comprising a spring loaded check valve in said return pipe means establishing a resistance to flow in the latter which is greater than the flow resistance of said check valve in the branch pipe, thereby to ensure that fluid will travel along said first conduit means from said branch pipe to said motor rather than to said control valve means when the latter is disposed in said braking and reverse drive position while said motor is rotating in the forward direction.

23. A hydraulic drive for centrifugals comprising:

a positive displacement reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter;

a prime mover;

variable volume pumping means driven by said prime mover;

a tank containing hydraulic fluid to be delivered under pressure by said pumping means;

control valve means connected to said pumping means to receive the fluid under pressure delivered by the latter;

first and second conduit means extending from said control valve means to said motor and alternately carrying hydraulic fluid to and from said motor for effecting forward and reverse rotation of the latter;

return pipe means extending from said control valve means to said tank;

said control valve means having a forward drive position in which said pumping means and first conduit means are connected while said second conduit means communicates with said return pipe means,

a braking and reverse drive position in which said pumping means is connected to said second conduit means while said first conduit means communicates with said return pipe means,

and a rest and coasting position in which said pumping means is connected to said return pipe means while said first and second conduit means communicate with each other;

first and second pressure relief valves in said first and second conduit means, respectively, for limiting the pressure of hydraulic fluid in the related conduit means;

a check valve in said second conduit means permitting flow through the latter only in the direction from said motor to said second pressure relief valve;

a bypass conduit connected to said second conduit means around said check valve in the latter so that flow can occur through said bypass conduit [in the direction toward said motor during reverse rotation of the latter;

and flow restricting means in said bypass conduit for providing a relatively slow speed of reverse rotation of said motor.

24. A hydraulic drive for centrifugals as in claim 23; wherein said flow restricting means is adjustable; and further comprising actuating means for said adjustable flow restricting means operative in response to increases in the pressure in said second conduit means between said check valve and said motor to cause said flow restricting means to permit an increased rate of flow to the motor, thereby to compensate for increased leakage occurring in the motor with increased loading and tending to maintain a substantially constant slow speed of reverse rotation.

25. A hydraulic drive for centrifugals as in claim 24; wherein said actuating means includes a servo-motor having a movable member connected to said adjustable flow restricting means and being spring urged in the direction for decreasing the rate of flow of fluid through said flow restricting means, and means connecting said servo-motor to said second conduit means so that said pressure in the second conduit means between said check valve and said motor acts in the servo-motor against said movable member to displace the latter in the direction for increasing the rate of flow through said flow restricting means.

26. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, conduit means connected to said motor and forming a circuit through which hydraulic fluid can travel to and from said motor in opposite directions for effecting forward and reverse rotation of the motor, a prime mover, first and second pump means driven by said prime mover to respectively deliver relatively large and small flows of hydraulic fluid, and valve means disposed between said pump means and said circuit in a position to receive the flow from both of said pump means and operative in one position thereof to deliver the combined flows of said first and second pump means through said circuit in the direction for forward rotation of the motor, in another position thereof to deliver the relatively small flow of said second pump means through said circuit in the direction for reverse rotation of the motor while diverting the flow of said first pump means to a fluid reservoir, and in a third position thereof to divert the flow of both of said pumps to said fluid reservoir.

27. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a load such as a centrifugal basket for driving the latter, a prime mover, first and second pump means driven by said prime mover to respectively deliver relatively large and small flows of hydraulic fluid, a tank for containing hydraulic fluid to be delivered under pressure by said pump means, first and second conduit means extending from said motor to alternately carry fluid under pressure to and from said motor for effecting forward and reverse rotation of said motor, first and second piloted pressure relief valves connected to said first and second conduit means, respectively, and each having a loaded condition, in which said relief valve determines the maximum pressure in the related conduit means, and an unloaded condition, in which the relief valve dumps the hydraulic fluid received thereby back to said tank, means conducting the flow of fluid from said first pump means to said first piloted relief valve, and control means operative, in one position, to direct the flow from said second pump means to said second piloted relief valve and, in another position, to direct said flow from the second pump means to said first piloted relief valve, each of said piloted relief valves assuming said loaded condition thereof only in response to said flow from said second pump means so that, with said control means in said one position, said flow from the second pump means is delivered through said second conduit means to said motor to cause reverse rotation of the latter and, with said control means in said other position, the combined flows of said first and second pump means are delivered through said first conduit means to said motor to cause forward rotation of the latter.

28. A hydraulic drive for centrifugals as in claim 27; wherein said second conduit means has a check valve interposed therein to permit flow therethrough only in the direction from said motor to the pressure relief valve means in said second conduit means; and further comprising bypass conduit means connected to said second conduit means around said check valve in the latter so that fluid under pressure can flow through said bypass conduit means in the direction toward said motor for effecting reverse rotation of the latter, and flow restricting means interposed in said bypass conduit means to limit the rate of flow therethrough and thereby provide a relatively slow speed of reverse rotation.

29. A hydraulic drive for centrifugals as in claim 27; wherein said second conduit means has a check valve interposed therein to permit flow therethrough only in the direction from said motor to the pressure relief valve means in said second conduit means; and further comprising bypass conduit means connected to said second conduit means around said check valve in the latter so that fluid under pressure can flow through said bypass conduit means in the direction toward said motor for effecting reverse rotation of the latter, flow restricting means interposed in said bypass conduit means to limit the rate of flow therethrough and thereby provide a relatively slow speed of reverse rotation and means operative in response to variations in the load on said motor to vary the rate of flow through said restricting means in compensation for variations in the leakage in the motor resulting from said load variations and thereby maintain the speed of reverse rotation substantially constant.

30. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, a prime mover, pumping means driven by said prime mover, a tank containing hydraulic fluid to be delivered under pressure by said pumping means, control valve means connected to said pumping means to receive the fluid under pressure delivered by the latter, first and second conduit means extending from said control valve means to said motor and alternately carrying hydraulic fluid to and from said motor for eifecting forward and reverse rotation of the latter, return pipe means extending from said control valve means to said tank, and first and second pressure relief valves in said first and second conduit means, respectively, for limiting the pressures of hydraulic fluid in the related conduit means, said control valve means having a forward drive position in which said pumping means communicates with said first conduit means and said second conduit means communicates with said return pipe means, a reverse drive position in which said pumping means communicates with said second conduit means and said first conduit means communicates with said return pipe means, and a braking position in which said second conduit means is blocked, so that said second pressure relief valve determines the maximum pressure in said second conduit means for braking forward rotation of the motor, and in which said pumping means communicates with said first conduit means and said return pipe means to dump the pressure of said pumpingmeansback to said tank while ensuring an adequate supply of relatively cool hydraulic fluid from said tank to the motor through said first conduit means.

31. A hydraulic drive for centrifugals comprising a positive displacement, reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter, a prime mover, pumping means driven by said prime mover, a tank containing hydraulic fluid to be delivered under pressure by said pumping means, control valve means connected to said pumping means to receive the fluid under pressure delivered by the latter, first and second conduit means extending from said control valve means to said motor and alternately carrying hydraulic fluid to and from said motor for efifecting forward and reverse rotation of the latter, return pipe means extending from said control valve means to said tank, pressure relief valve means interposed in the connection between said pumping means and said control valve means to limit the pressure of hydraulic fluid in said connection, and connecting pipe means extending between said pressure relief valve means, said return pipe means and said first and second conduit means and having check valve means therein to permit flow from said connecting pipe means into said first and second conduit means, said control valve means having a forward drive position in which said pumping means and first conduit means are connected while said second conduit means communicates with said return pipe means, a, reverse drive and braking position in which said pumping means communicates with said second conduit means and said first conduit means communicates with said return pipe means, while said pressure relief valve means determines the maximum pressure in said second conduit means for braking of for ward rotation of the motor, and a rest and coast position inwhich said pumping means, said first and second conduit means and said return pipe all communicate with each other.

32. A hydraulic drive for centrifugals comprising:

a positive displacement reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter;

a prime mover;

first and second pumping means driven by said prime mover;

a tank for containing hydraulic fluid to be delivered under pressure by each of said pumping means;

first and second conduit means extending between said first pumping means and said motor and between said second pumping means and said motor, respectively, and alternately carrying fluid under pressure to and from said motor for effecting forward and reverse rotation of said motor;

piloted pressure relief valve means in each of said conduit means having a loaded condition in which said valve means determines the maximum pressure in the related conduit means,

and an unloaded condition in which the valve means dumps the fluid carried to it through the related conduit means back to said tank;

and control valve means operative selectively to unload one of said pressure relief valve means while loading the other of said pressure relief valve means,

and to unload said other pressure relief valve means while loading said one pressure relief valve means.

33. A hydraulic drive for centrifugals as in claim 27:

each of said relief valves in its loaded condition determining the maximum pressure in the related conduit means by dumping'fluid to said tank;

and further comprising means operative, when the fluid supply to said motor through one of said conduit means is interrupted with the motor rotating in the direction effected by delivery of fluid thereto through that conduit means, to supply to that conduit means and'thence to said motor an amount of the fluid bemg dumped by saidpressure relief valves to said tank suflicient to prevent cavitation in said motor as the motor continues to rotate in said direction due to the momentum of said load.

34. A hydraulic drive for centrifugals as in claim 15:

further comprising a check valve in said return pipe means allowing flow therethrough only in the direct1on toward said tank,

said check valve in said return pipe means imposing a resistance to flow therepast which is greater than that imposed by the check valve in either of said connecting pipe means.

35. A hydraulic drive for centrifugals as in claim 15:

wherein said second conduit means has a check valve interposed therein to permit flow therethrough only in the direction from said motor to the pressure relief valve means in said second conduit means;

and further comprising bypass conduit means connected to said second conduit means around said check valve in the latter so that fluid under pressure can flow through said bypass conduit means in the direction toward said motor for effecting reverse rotation of the latter,

and flow restricting means interposed in said bypass conduit means to limit the rate of flow therethrough and thereby provide a relatively slow speed of reverse rotation. 36. A hydraulic drive for centrifugals as in claim 22: wherein said second conduit means has a check valve interposed therein to permit flow therethrough only in the direction from said motor to the pressure relief valve means in said second conduit means; and further comprising bypass conduit means connected to said second conduit means around said check valve in the latter so that fluid under pressure can flow through said bypass conduit means in the direction toward said motor for effecting reverse rtation of the latter, and flow restricting means interposed in said bypass conduit means to limit the rate of flow therethrough and thereby provide a relatively slow speed of reverse rotation. 37. A hydraulic drive for centrifugals as in claim 30: said second pressure relief valve determining the said maximum braking pressure in said second conduit by dumping fluid from that conduit to said tank; and further comprising means operative as the forward rotation of the motor is being braked to deliver to said first conduit means an amount of the fluid being dumped by said second pressure relief valve sufficient to prevent cavitation of the motor. 38. A hydraulic drive for centrifugals as in claim 30: wherein said second conduit means has a check valve interposed therein to permit flow therethrough only in the direction from said motor to the pressure relief valve in said second conduit means; and further comprising bypass conduit means connected to said second conduit means around said check valve in the latter so that fluid under pressure can flow through said bypass conduit means in the direction toward said motor for effecting reverse rotation of the latter, and flow restricting means interposed in said bypass conduit means to limit the rate of flow therethrough and thereby provide a relatively slow speed of reverse rotation. 39. A hydraulic drive for centrifugals as in claim 37: further comprising bypass conduit means extending from said second pressure relief valve to said tank to receive the fluid dumped by that valve,

said bypass conduit means having a flow restrictor therein; said operative means including branch conduit means extending from said bypass conduit means at a location along the latter between said second pressure relief valve and said restrictor to said first conduit means at a location along the latter between said first pressure relief valve and said motor and having a check valve therein permitting fluid flow only toward said first conduit means;

said restrictor imposing a greater resistance to the flow of liquid therepast than is imposed by said check valve so that as the forward rotation of the motor is being braked an amount of the fluid being dumped by said second pressure relief valve is supplied to said first conduit means to prevent cavitation in said motor. 40. A hydraulic valve for centrifugals as in claim 31: wherein said second conduit means has a check valve interposed therein to permit flow therethrough only in the direction from said motor to the control valve means; and further comprising bypass conduit means connected to said second conduit means around said check valve in the latter so that fluid under pressure can flow through said bypass conduit means in the direction toward said motor for effecting reverse rotation of the latter,

and flow restricting means interposed in said bypass conduit means to limit the rate of flow therethrough and thereby provide a relatively slow speed of reverse rotation.

41. A hydraulic drive for centrifugals as in claim 26:

further comprising unloading valve means interposed in said circuit and operative with said control valve disposed in said one position to unload one of said pump means until the full output of the other of said pump means is being utilized by the motor whereby to reduce the peak load on said prime mover as well as the heating of the circulated hydraulic fluid.

42. A hydraulic drive for centrifugals comprising:

a positive displacement reversible rotary hydraulic motor adapted to be directely coupled to a centrifugal basket for driving the latter;

a prime mover;

separate relatively high capacity pumping means and relatively low capacity pumping means both driven by said prime mover;

a tank containing hydraulic fluid to be delivered under pressure by said pumping means;

conduit means extending between said pumping means and said motor and forming a circuit through which hydraulic fluid can travel to and from said motor in opposite directions for effecting forward and reverse rotation thereof and to which both of said pumping means continuously deliver fluid when said prime mover is operating;

and means including a control Valve and operable in one position of said control valve to dump the entire ouput of said low capacity pumping means from a location in said conduit means ahead of said motor to said tank while directing the output of said high capacity pumping means through said conduit means to said motor in a direction to produce relatively rapid forward rotation thereof,

and operable in another position of said control valve to dump the entire output of said high capacity pumping means from a location in said conduit means ahead of said motor to said tank while directing the output of said low capacity pumping means through said conduit means to said motor in a direction to produce relatively slow reverse rotation thereof.

43. A hydraulic drive for centrifugals comprising:

a positive displacement reversible rotary hydraulic motor adapted to be directly coupled to a centrifugal basket for driving the latter;

a prime mover;

pumping means driven by said prime mover;

a tank containing hydraulic fluid to be delivered under pressure by said pumping means;

a control valve;

means for carrying hydraulic fluid from said pumping means to said control valve;

first and second conduit means extending from said control valve to said motor for carrying hydraulic fluid to and from said motor in opposite directions for effecting forward and reverse rotation thereof;

piloted pressure relief valve means in each of said conduit means,

each of said pressure relief valve means having a loaded condition in which it determines the maximum pressure in the related conduit means,

and an unloaded condition in which it dumps the fluid carried to it through the related conduit means to said tank;

said control valve being operable selectively to load said first relief valve and unload said second relief valve while directing the fluid de livered to it from said pumping means through said first conduit means,

and to load said second relief valve and unload said first relief valve while directing the fluid delivered to it from said pumping means through 5 said second conduit means.

References Cited in the file of this patent UNITED STATES PATENTS Huguenin Oct. 27, 1931 10 Ferris et al May 30, 1933

Claims (1)

1. 2. A HYDRAULIC DRIVE FOR CENTRIFUGALS COMPRISING A POSITIVE DISPLACEMENT, REVERSIBLE ROTARY HYDRAULIC MOTOR ADAPTED TO BE DIRECTLY COUPLED TO A CENTRIFUGAL BASKET FOR DRIVING THE LATTER, CONDUIT MEANS CONNECTED TO SAID MOTOR AND FORMING A CIRCUIT THROUGH WHICH HYDRAULIC FLUID CAN CIRCULATE TO AND FROM SAID MOTOR IN OPPOSITE DIRECTIONS FOR EFFECTING FORWARD AND REVERSE ROTATION OF SAID MOTOR, A PRIME MOVER, PUMPING MEANS DRIVEN BY SAID PRIME MOVER AND DELIVERING HYDRAULIC FLUID UNDER PRESSURE TO SAID CIRCUIT, CONTROL MEANS SELECTIVELY DETERMINING THE DIRECTION OF CIRCULATION OF HYDRAULIC FLUID THROUGH SAID

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