US2258981A - Selective delivery reduction means for variable delivery pumps - Google Patents

Description

W. ERNST Oct. '14, 1941.

SELECTIVE DELIVERY REDUCTION MEANS FDR "VARIABLE DELIVERY PUMPS- s Sheeiis-Sheet 1 Filed Sept. 16, 1938 m W\ 8 c M us R 5.:

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INVENI'I'OR. WALTER must ATTORNEYS Oct. 14, 1941. w ERNST 2,258,981

SELECTIVE DELIVERY REDUCTION MEANS FOR VARIABLE DELIVERY PUMPS Filed Sept. 16, 1938 5 Sheets-Sheet 2 IN VENTOR. WA LTER ERN ST SW 7 YMMV- ATTORNEY5 Oct. 14, 1941. w. ERNST 2,258,981

. SELECTIVE DELIVERY REDUCTION MEANS FOR VARIABLE DELIVERY PUMPS Filed Sept. 16, 1938 3 Sheets-Sheet 5 IN VENTOR.

q WALTER ERNST l BY ATTORNEY;

Patented Oct. 14, 1941 UNIT-ED sTATEs PATENT OFFICE SELECTIVE DELIVERY REDUG'IION MEANS FOR VARIABLE DELIVERY PUMPS Walter Ernst, Mount Gilead, Ohio, assignor to -The Hydraulic Press Corp. Inc., Wilmington,

Del., a corporation of Delaware Application September 16, 1938, Serial No. 230,260

(01. GIL-52) delivery pump circuit supplying pressure fluid to a hydraulic motor in response to the motion of said motor, or a portion-thereof, to. a predetermined position.

Another object is to provide a delivery-regulating device for a variable delivery pump circuit which will cause a reduction of pump output and hence a slowing down of the hydraulic motor connected thereto when the. movable motor member, such as the ram, reaches a predetermined position, preferably before engaging the workpiece or the opposing member.

Another objectls to provide a hydraulic pressoperating circuit having a hydraulic motor and a variable delivery pump of such a character that the delivery of the variable delivery fpump is reduced when the plunger of the hydraulic motor reaches a predetermined position, and particularly before the movable member of the press engages the stationary. member or workpiece, and

also before the motor has encountered substan-, tial resistance to its operation.

Another object is to provide a variable delivery pump and a control unit'therefor which is adapted to shift the flow-control element of the pump independently of the shifting accomplished by an additional piston responsive to the attainment of a predetermined pressure in the circuit served y he pump- Another object is to provide such-a control unit for a variable delivery ,pump', wherein packings are reduced to a minimum and are substantially eliminated, thereby eliminating to a great extent .the friction arising from the presence of such packings and correspondingly increasing the sensitivityof the control unit.

In the drawings:

Figure l is a side elevation, partly in section, of a' hydraulic press-operating circuit including means for selectively reducing the delivery of a variable delivery pump when the press platen reaches a predetermined position, the press having an upwardly acting ram including a booster ram. v

Figure 2 is a modification of the circuit shown in Figure l, with a downwardly acting press ram and without a booster ram.

Figure 3 is an enlarged longitudinal section through the control mechanism of the variable delivery pump for providing selective fluid delivery' reduction according to the present invention,

with the moving pistons disengaged to render the unit temporarily inoperative.

Figure 4 is a view similar to Figure 3, but with the pistons engaging one another and shifted to their extreme right-hand positions by the spring unit of the variable delivery pump.

' General construction In general, the invention consists of a device for altering the delivery of a variable delivery pump by the control rod thereof when the press plunger of a press reaches a predetermined position. When the press plunger reaches that position it shifts a valve, whereupon pressure fluid is admitted to a piston mounted on the control rod of the'variable delivery pump, and this piston shifts the control rod and the shiftring of the pump to reduce the delivery of the pump. This action occurs before the press plunger engages the workpiece or before a substantial resistance has been built up to oppose the motion of the press plunger.

In many applications of hydraulic motors, and particularly hydraulic presses, it has been found desirable to move the press plunger or platen rapidly toward the work, and then to cause it to move more slowly. In plastic molding machines,

1 for example, where a synthetic plastic material,

such as a synthetic resin, is placed in the mold in the form of a powder or briquette which must be softened by heat before it will flow readily into the more intricate portions of the mold cavity, it is essential that the mold halves be moved very-slowly during the final portion of the clostion from rapid to slow motion shall take place ing stroke. It is also advisable that the transibefore any substantial resistance has been encountered in closing the molds. Other applications of hydraulic motors also occur, where it is desirable to provide an initial high speed and a final slow speed; with the shifting point brought about at a predetermined position rather than by the attainment of a predetermined resistance to' the progress of the plunger of a movable motor member.

Hitherto, it has been attempted to-control the output of a. variable delivery pump to efl'ect a reduct in in its output after the work has been engaged, or when a predetermined resistance has been built up. The present invention, however, and the arrangement of the control circuit enable a selective reduction of the pump output,

and hence, a slowing down of the driven mechanism, such as the hydraulic motor, before the work is engaged or a substantial resistance has been built up.

In general, a typical circuit for accomplishing the objects of this invention is shown in Figure 1, and consists of a variable delivery pump I having a spring-urged device H for urging the flow-control element oi. the pump in one direction, and a pump control unit |2 for urging it in the opposite direction. A tank l3 supplies fluid for the operation of the circuit, and contains a check valve I4 for purposes hereinafter explained. A four-way main control valve I5' and a two-way auxiliary valve I6 are provided for the regulation of the supply of fluid to the motor of the hydraulic press H. A choke or fluid flow-restricting element I8 is optionally inserted in the circuit of Figure l, and is regularly inserted in the circuit of Figure 2. The auxiliary two-way valve i6 is operated by the motion of the platen of the press H at a predetermined position, as hereinafter explained.

Variable delivery pump control arrangement The variable delivery pump I8 is of the radial piston type well known to those skilled in the art, but any other type of variable delivery pump may be employed, the radial piston type being merely shown for purposes of example. The variable delivery pump I8 is provided with a flow-control element or shiftring 20, which is mounted upon the control rods 2| and 22 slidably supported in the pump casing 23 and passing outwardly therethrough. The shiftring' 28 ordinarily encircles the secondary rotor of the pump and by varying the eccentricity of the latter relatively to the axis of rotation of the primary rotor or cylinder barrel alters the delivery or output of the pump. When the axis of the secondary rotor coincides with that of the primary rotor or cylinder barrel, and the eccentricity is zero, the shiftring 28 is then said to be in its neutral or zero delivery position. Under these circumstances, as is well known to those skilled in the hydraulic art, the pistons of the pump l0 will not reciprocate and hence the pump delivers substantially no fluid.

The control rod 2| is urged to the right to shift the shiftring or flow-control element 28 into a full delivery position by the spring-urged device consisting of a stationary tubular casing 24 within which is telescopically mounted a movable tubular casing 25. The stationary casing 24 is secured to the pump casing 23 and both casings 24 and 25 inclose a coil spring 26, one end of which rests against the inner left end wall of the stationary casing 24, whereas the other end engages the right-hand end wall of the movable casing 25, which has a ball thrust bearing 21 associated therewith and engaged on its opposite side by the hub oi. a hand wheel 28 internally threaded upon the threaded portion 29 of the control rod 2|. A locknut 38 beyond the hand wheel 28 enables the locking of the hand wheel 28 in any desired position of adjustment. The

control unit |2, in general, urges the control rod 22 and pump shiitring 28 to the left when it receives pressure fluid, thereby tending to overcome the thrust of the coil spring 26 and move the shiftring 28 back toward its zero delivery or neutral position.

The control unit |2 (Figure 3) consists of a housing 3| attachable by its flanged portion 32 to the pump casing 23. This housing 3| contains a cylinder bore 33 having a threaded entrance port 34, giving access to the endthereor nearest the pump casing 23. Reciprocable within the cylinder bore 33 is an auxiliary piston 35 having sleeve-like extensions or hubs 36 and 31 extending in opposite directions along the control rod 22 but separated therefrom by a substantial clearance space 38 therebetween. Fluid leaking past the auxiliary piston 35 to the lefthand end of the cylinder bore 33 escapes by way of the transverse passageway 38 into the clearance space 38, and thence along the control rod 22, back into the pump casing 23, the clearance space 38 forming the annular passageway along the control rod 22. An accurate sliding fit is maintained in the bore 48 between the hub 36 and the casing 3| so that no packing is required at this location. The hub 31, however, is separated by a clearance space 4| from the cylinder head 42, which is bolted to the housing 3| by means of the screws 43 and with the gasket 44 therebetween to prevent leakage.

Bolted to the cylinder head 42, as by the screws 45, is a housing 46 containing a cylinder bore, generally designated 41, and receiving a stepped piston, generally designated 48. The stepped piston 48 consists of three portions 48, 50 and 5|, of different diameters, respectively reciprocable in the bore portions 52, 53 and 54 of the cylinder bore 41. This construction provides annular piston areas 55 and 58 opening into bore enlargements 51 and 58, served by the threaded ports 58 and 68; and also provides an annular end wall 6| which is adapted to be engaged by the annular end wall 62 of the piston hub 31 when the piston 48 is moved to the right to close up the space (Figure 3) between the annular end walls 6| and 62, in the manner shown in Figure 4. For this purpose the stepped piston 48 is separated from the control rod 22 by a clearance space 63, similar to'the clearance space 38 between the auxiliary piston 35 and the control rod 22.

The outer end of the control rod 22 is threaded, as at 64 (Figure 3), and provided with a locknut 65 engaging a collar 66, which, in turn, engages the conicalbore 61 in the end of the stepped piston 48. A longitudinal passageway 68, communicating with a transverse passageway 69 in the control rod 22, provides for the drainage of fluid which escapes past the stepped piston 48.

In Figure 3 the stepped piston 48 is shown as separated by a quarter of an inch from the auxiliary piston 35, yet the latter is at the extreme end of its stroke in the left-hand direction. This separation between the end walls GI and 62 of the piston portions 5| and 31, respectively, is provided to render the unit l2 temporarily inoperative at the will of the operator. 'When it is desired to render the unit operative (Figures 1 and 4), the operator rotates the locknut 65, thereby moving the stepped piston 48 to the right, along the control rod 22, until the end wall 6| engages the end wall 62. Thus, when pressure is admitted through the port 34 to the cylinder bore 33 so as to urge the auxiliary piston 35 to the left, the la ter likewise engages the end wall 6| of the stepped piston 48, moving it to the left and with it the control rod 22 by reason of the connection provided by the collar 66 and locknut 85. The locknut 65 may be locked atany desired position along the threaded portion 68 by'turning the set screw 10. The left-hand end of the cylinder bore 41 is closed by the end plate 1|, secured to the housing 46 bythe screws 12, leakage being prevented by the gasket 13.

The stepped piston 48 is provided for the purpose of creating a multiplicity of piston areas of different sizes 'so that the pump flow-control element or shiftring 20 may be shifted to its neutral position at one of a plurality of selected pressures. The particular pressure selected is determined by whether the control conduit is connected to .the port 60 or. to the port 59. In the example shown in Figure 3, the port 59 is illustrated as closed by the threaded plug 14 so that the port 60, cylinder bore 53 and annular piston area 56 are in use. The same arrangement is shownin Figure 1. It will also be obvious that a third piston area will be available if both of the ports 59 and 60 are connected to the pressure circuit, thereby subjecting the combined piston areas 56 and 55 to the action of the pressure fluid. The stepped piston construction shown at the left-hand end of Figure 3 in itself is described and claimed in the copending application of Ernst, et al., Ser. No. 225,155, filed August 16, 1938, now Patent No. 2,229,965.

I It will be observed that the motion of the auxiliary piston 35 to the left is limited by the shoulder at the end of the portion 16 containing the transverse passageway 39. In Figure 3 theauxiliary piston 35 is shown in its extreme lefthand position, which position it will occupy only when there is suflicient pressure in the cylinder bore 33 to overcome the force of the coil spring 26. By turning the locknut 65 the amount of movement of the control rod 22, which may be auxiliary piston 35 assist in preventing leakage thereby, but where such leakage occurs it is rapidly taken care of by the leakage system previously described and consisting of the passages 39, 68 and 69 and the clearance spaces 63 and 38 surrounding the control rod 22. The thrust of the spring 26 and therefore the force opposing the action of the pistons 35 and 48 is regulated by turning the hand wheel 28.

Hydraulic press circuit with upwardly moving platen and booster mm The variable delivery pump with the control unit described above is capable of a variety of uses, Figure 1 showing the press having an upward1y.moving platen and a booster ram. In Figure 1 the press I1 is provided with a head 80, a bed 8I interconnected by the strain rods 82 having the nuts 83 threaded upon the ends thereof. The press I1 is provided withan upwardly moving platen 84, to which is attached the main plunger 85 having a piston head 86 reciprocable in the main cylinder bore 81,'the entrance to which is closed by the packing 88 and gland 89. The main plunger 85 is hollow and contains a. booster cylinder 90, the walls of which are engaged by the end of the booster ram 9|, which consists of a hollow tube mounted in the aperand having a bore 94 extending longitudinally its closing position than would be possible by using the piston-area 95 of the main plunger alone.

The platen 84 may operate in any manner upon the workpiece or upon the other mechanism to be operated. In Figure 1 the platen 84, for purposes of example, is shown as carrying a die half 96 cooperating with the stationary die half 91 mounted uponthe press head 80. The platen 84 is also provided with a platen arm 98 adapted to engage a collar 99 upon the valve rod' I00 of the twoway auxiliary valve -I6, previously described. An additional collar IN is provided beneath the platen arm 98 so that the latter will shift the valve rod I00, and change the setting of the twoway valve I6 at the opposite endsof its stroke.

The variable delivery pump is connected to the tank I3 by the suction conduit I02 from the suction connection I03. The fluid received along the suction conduit I02 is pumped-through the pressure head I04, along the conduit I05 to the four-way main control valve I5 having the valve rod I06. From the valve I5 the discharge conduit I01 leads back to the tank I3, and the conduits I08 and I09 lead respectively to the upper end' of the main cylinder bore 81 and to the twoway auxiliary valve I6. A branch conduit I I0 leads from the conduit I09 to the bore 94 within the stationarybooster ram 9I. A conduit III leads from the two-way valve I6 to the port H2 in the lower end of the main cylinder bore 81,

and in this conduit a choke I8 is optionally inserted. A branch conduit I I3 runs from the conduit III to the check valve I4 withirrthe tank I3.

A control conduit II4 also runs from the conduit' III to the port 34 of the cylinder bone 33, whereas the control conduit II5 runs from the pressure conduit I05 to either or both of the ports 59 and 60, adapted to admit pressure fluid to the stepped piston 48.

. In the operation of the circuit shown in Figure 1, the variable delivery pump I0 is started in opduits I09 and H0 and the bore 94 of the booster plunger 9|, into the booster cylinder 90, the auxiliary valve I6 being in its lowered or closed position. Pressure fluid within the booster cylinder acts against the limited area thereof and causes the main plunger 85 and platen 84 tobe moved upwardly at a rapid rate. The void thus produced in the main cylinder bore 81 is filled with fluid through the port 'I I2, the conduits III and I I3 and the check valve I4 from the tank I3.

When the lower mold half 96 has almost reached the upper mold half 91, or at any desired point in the operation of the press I1, the platen arm 98 engages the collar 99 and lifts the valve rod I00 of the auxiliary valve I6, opening the latter by shifting its heads to the positions shown in Figure 1. Since the pressure fluid can now pass from the conduit I09 throughthe'auxiliary valve I6, and the conduit III and port II2, into' ture 92 at the lower end of the main cylinder 93, 75 the main cylinder bore 81, it encounters less resistance therein than in the booster cylinder 94. Most of the discharge from the variable delivery pump III, on this account, will nowbe diverted to the main cylinder bore I4, where it acts against the large piston area 95 thereof, with the result that a sufllcient pressure will be produced to contlnue the lifting of the main plunger 85 but at a reduced speed and with a much greater potential pressing force. Pressure fluid now backs up in the conduit H4 and passes through the port 34 (Figure 3), into the cylinder bore 33, where it acts against the piston head 35 and moves it to the left. 4

Assuming that the stepped piston 48 has been brought into operative engagement by rotating the nut 65 in a clockwise direction (Figure 4) and the gap between the end walls 6i and 62 is closed up from the position shown in Figure 3 to that shown in Figure 4, the motion of the piston 35 will be transmitted to the control rod 22, shifting the latter to the left by overcoming the thrust of the coil spring 26. This movement shifts the flow-control element or shiftring of the pump I4 toward its neutral or zero delivery position, thereby reducing the delivery of the pump in and placing the latter upon part stroke. The amount of reduction in pressure depends upon the adjustment of the nut 65. This reduction in the discharge of the pump it thus slows up the movement of the main plunger 44, the speed of which can be adjusted by adjusting the nut 55. The

area of the piston head is preferably made sufliciently large so that the pressure, due to the weight of the moving parts 44 and 45, will be sumcient to cause the shifting of the piston head 44 to the left as soon as the two-way valve I4 is opened by the engagement of theplaten arm 44 with the collar 99 on the control rod I04.

However, the weight of these moving parts may not be sufllciently large to provide enough pressure to shift the piston head 44, as may occur in the case of a downwardly acting press plunger ,with a booster cylinder in which no pressure would build up because the ram travels downwardly under the influence of gravity. In that event the choke Il may be inserted in the con duit III, as shown by the dotted lines in Figure 1. This choke I4 artificially increases the pressure in the conduit-i I4 and therefore causes the Piston head 44 to move.

The piston head 44' is intended to reduce the stro keci the pump but not to reduce it to zero.

'Thus,ai'ter the two-way valve I4 is opened at a predetermined point in the motion of the platen 44, the pump I4 is on part stroke and is still delivering pressure fluid. when the main plunger 44 meets a 'suflicient positive resistance so that.

collar IIII and closes the two-way valve I4. Pressure then builds up in the circuit and backs up in the conduit Hi to shift the stepped piston 44, the control rod 22 and shiftrlng 24 to the left to reduce the discharge of the pump III substantially to 'zero.

ing plunger without booster ram The-modified circuit in Figure 2 employs the same variablie delivery pump III, with its spring unit II and control unit I2 as previously described.- The four-way valve I5 is likewise the same as in Figure 1. The two-way valve II4, however, diners from the two-way valve I4 of Figure 1 by having a coil spring 4" urging the valve rod IIS upwardly into its open positlon,.so that the valve lit is a normally open valve. The valve rod H9 is provided with acollar I24, arranged in close proximity to the press I". The latter diflers from the press I! of Figure 1 by having a downwardly acting plunger 4 without a booster plunger, as in Figure 1.. The plunger I I4 is provided with a piston head I I4 reciprocablein the main cylinder bore I2I. The ports I22 and I22 lead, respectively, into the upper and lower ends of the main cylinder bore I2I. The

r main plunger H8 is provided with an arm I24 adapted to engage the collar I24 and close the auxiliary valve II4 when the main plunger II4 has descended to a predetermined position, as regulated by the position of the collar I24 on the valve rod H4.

The tank I 24 is connected the conduit I26,

to the pump III by from which the conduit I21 runs to the discharge side of the main control valve II, the pressure side of which is connected by the conduit I28 to the pressure connection I44 of the pump Ill. The conduit I29, running from the pressure conduit I24 to the control unit I2, corresponds to the conduit III in the circuit of Figure 1, and the conduit I44 similarly corresponds to the conduit 4 of Figure 1. From the main control valve I! the conduit I3I runs to the the. pressure fluid backing up in the conduit IIS is of sumcient force to shift the stepped piston 44 to the left and-overcome the thrust of the coil spring 26, the control rod 22 and shiitring 24 of the pump are shifted to substantially neutral position. The pump in this position is arranged to deliver just enough fluid to take care of leakage in the circuit, if such leakage is present. To reverse the motion of the platen 44 the valve rod I44 of the main control valve I 5 is shifted to its opposite position, whereby pressure fluid is delivered to the conduit I44, into the space at the upper end of the main cylinder bore 41.

Since the two-way valve It remains open until the platen arm 98 encounters the lower collar I" on the valve rod I44, fluid escapes from the lower end of the main cylinder bore 41, through the port II2, the'conduit I II, the two-way valve I4,

choke I4, from which the conduit I22 runs to the upper port I22 01' the main cylinder bore I24.

From the conduit iii a branch conduit I43 runs to the two-way auxiliary valve I I4,

from the opposite side of which the conduit I24 runs to a Junction with the conduit I22. The conduits I34 and I44 and the valve H4 thus provide a by-pass line around the choke II when the valve H4 is open. From the main control valve II the conduit I44 runs to the lower port I23 in the main cylinder bore I24 beneath the piston head III.

In the operation of the circuit of Figure 2 there is no booster circuit as in Figure 1.- The twoway va1ve,ho,wver, makes it possible to introduce resistance in the circuit and artificially increase the pressure acting upon the control unit I2 by means oi the choke I4. In the initial portion of the downward stroke of the'main plunger Ill the two-way valve In is held open by its coil spring H4. Fluid from the supply tank I24 enters the pump through the conduit I24, and is discharged through the conduit I24, the main control valve I5. the conduits iii and I24, the normally open auxiliary valve lit, the conduits I34 and I32 and the port I22, into the upper end oi the main cylinder bore I2I. It will be understood that a surge valve may be provided between the supply tank and the cylinder bore I2I to assist in the prefllling of the latter during the descent of the main plunger I18, but this surge valve has been omitted for the sake of simplifying the showing.

The main plunger H8 descends until the arm I24 engages the collar I20 and shifts the valve cylinder, said control piston being movable inde-z pendently or said auxiliary piston and being re-.

sponsive to a predetermined pressure in said control cylinder for moving said flow control element the travel of said main plunger to a predeterrod IIS so as to overcome the urge of the coil spring I I5 and close the two-way auxiliary valve H5. The by-pass line aroundthe choke I8 is now'closed so that henceforth pressure fluid must flow from themain control valve I5. through the conduit I3I, the choke I8 and the conduit I32, into the port I22 at the upper end or the'main cylinder bore '2!- The resistance built up by the mined position during its advancing stroke for admitting pressure fluid to said auxiliary cylinder, whereby to reduce the flow from said pump to said maincylinder and to reduce the speed' of said main plunger, andmeans responsive to a predetermined point of travel of said main plunger during its retraction stroke for causing said main plunger to convey fluid pressure to said auxiliary piston for actuating the same so as to move said $ow control element to a restricted delivery posi-' ion.

2. In a hydraulic circuit, a main' cylinder, a main plunger therein, a variable delivery pump hydraulically connected; to said main cylinder and having a movable flow control element, yielding means for urging said flow control element L in',a flow-increasing direction, an auxiliary cylingly reduced. If a surge valve has been used to preflll the main cylinder bore I2I during the in- While the circuit shown in Figure 2 has been illustrated as operating in connection with a downwardly acting press, it will be evident that the, arrangement inay be used with any hydraulic motor regardlessof whether the plunger 8 is downwardly acting, upwardly acting or horizontal. To reverse th motion of the main plunger I I8 and retract it, the main control valve 1 I5 is shifted to its opposite position so that pres sure fluid is discharged through the conduit I and' port I23 beneath the piston head H8, thereby raising the main plunger H8. The arm I24 thereupon releases the collar I20 so that the valve rod H9 moves upwardly, under the urge of the coil spring U5, and shifts the auxiliary valve I I6 to its normally open position. Fluid can then escape through the port I22, the conduit I34, the valve I I8, the conduits I33 and I3I, the main control valve I5 and the conduits I21 and I26, back into the supply tank I25.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims and the invention. r

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a hydraulic circuit, a "main cylinder, a I

main plunger therein, a variable delivery pump hydraulically connected to said main cylinder and having a movabl fiow control element, yielding means for urging said flow control element in a flow-increasing direction, an auxiliary cylinder,

* an auxiliary piston therein connected to move inder, an auxiliary piston therein connected to move said flow control element in a flow-reducing direction, a control cylinder constantly connected to the pump discharge, a control piston in said cylinder, said control piston being movable independently of said auxiliary piston and being responsive to a, predetermined pressure in said con- I flow-restricting means and.admitting said pressure to said auxiliary cylinder, thereby moving said flow control direction.

3. Ina hydraulic circuit, a main cylinder, a

'- main plunger therein, a variable delivery pump control cylinder for moving said control element to its zero deliveryposition, a fluid flow-restricting device hydraulically connected with said auxiliary cylinder and adapted to convey pressure fluid from said pump to said main plunger, conduit mean for conveyin fluid from said pump to said main plunger withoutpassing through said flow-restricting device, 'means adapted in response to the travel of, said main plunger to a predetermined position to pass pressure fluid from said pump to said mainplunger through said flow-restricting device, and means adapted in response to a second predetermined pressure, less than said first mentioned pressure, and prevailing between said flow-restricting device and said pump to actuate said auin'llary piston for causelement in said flow reducing.

ing the latter to move said flow control element into, a restricted delivery position.

4. In a hydraulic circuit, a main cylinder, a main plunger therein, a variable delivery pump hydraulically connected to said main cylinder and having a movable flow control element, yielding means for urging said flow control element in a flow-increasing direction, an auxiliary cylinder, an auxiliary piston therein connected to move said flow control element in a flow-reducing direction, a control cylinder constantly connected to the pump discharge, a control piston responsive to a predetermined pressure in said control cylinder for movingsaid flow control element to its zero delivery position, an auxiliary valve, and means responsive to the travel of said main plunger to two predetermined positions respec tively during the advancing and retraction stroke of said plunger for shifting said valve and admitting pressure fluid to said auxiliary cylinder, whereby to shift said flow control element and reduce the flow from said pump.

5. In a hydraulic circuit, a main cylinder, a main plunger therein having a main area and a booster area associated therewith, a variable delivery pump having a movable flow-control element, yielding means for urging said flow-control element in a flow-increasing direction, an auxiliary cylinder, an auxiliary piston therein, means for transmitting the thrust of said auxiliary piston to said flow-control element in the flow-reducing direction, an auxiliary valve arranged in one position to admit pressure fluid from said pump to said booster area and in another position to admit pressure fluid to said main area and to said auxiliary cylinder, and means responsive to the travel-of said main plunger to a predetermined position for shifting said valve to admit pressure fluid to said main area and to said auxiliary cylinder, whereby to shift said flowcontrol element and reduce the flow from said pump.

6. In a hydraulic circuit, a main cylinder, 9. main plunger therein having a main area and a booster area associated therewith, a variable delivery pump having a movable flow-control element, yielding means for urging said flow-control element in a flow-increasing direction, an auxiliary cylinder, an auxiliary piston therein, means for transmitting the thrust of said auxiliary piston to said flow-control element in the flow-reducing direction, an auxiliary valve arranged in one position to admit pressure fluid from said pump to said booster area and in another position to admit pressure fluid to said main area and to said auxiliary cylinder, a fluid flow-restricting device insertable in said circuit between'said main cylinder and said pump, and means responsive to the travel. of said main plunger to a predetermined position for operatin said valve to admit pressure fluid to said auxiliary cylinder and for directing the flow from said pump to said main cylinder through said flow-restricting device.

, to said flow-control member to move it in the flow-reducing direction, a valve arranged in a flrst position to admit pressure fluid from said pump to said booster cylinder and in a second position to admit pressure fluid to said main advancing area and to said auxiliary cylinder, means responsive to the travel of said main plunger to a predetermined position during its forward stroke to shift said valve from said flrst position to said second position to admit pressure fluid to said auxiliary cylinder to reduce the flow of said pump,

and means responsive to the travel of said main plunger to a predetermined position during its retraction stroke to shift said valve from said second position to said first position to cause fluid entrapped between said auxiliary cylinder and said advancing area to actuate said auxiliary piston so as to move said flow-control member in said flow-reducing direction.

8. In a hydraulic circuit. a main cylinder, a main piston having an advancing area and a retraction area, a variable delivery pump having a movable flow-control member, yielding means for urging said flow-control member in a flow-increasing direction, an auxiliary cylinder, an auxiliary piston therein connected to said flow-control member and adapted to move the same in a flow-reducing direction, a four-way valve movable selectively into one of two positions to admit pressure fluid from said pump to said advancing area while releasing fluid from said retraction area, or vice versa, a two-way valve adapted in a first position to eii'ect communication between said four-way valve and said advancing area and ma second position to interrupt said second position. WALTER ERN ST.

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