US2004793A - Hydraulic apparatus - Google Patents

Description

.lime 11, 1935. D, H, MWTGQMERY 2,004,793

HYDRAULIC APPARATUS Filed Jain. 129, 1931 4 sheets-sneer l June 1l, 1935. D. HQMoNrGoMgRY v 2,004,793

HYDRAULIC APPARATUS Filed Jan. 29, 1931 4 Sheets-Sheet 2 Jmtov June 11, 1935. D; H. MoN'rGoMl-:RY 2,004,793 f I HYDRAULIC APPARATUS Filed Jan. 29, 1931 4 Sheets-Sheet 3 Patented .nine 11', 193s PATENT OFFICE HYDRAULIC APPARATUS Donald H. Montgomery, Berlin, Conn., assignor to The New Britain-Gridley Machine Company,

New Britain, Conn., necticut Application January 29,

23 Claims.

ated with a relatively quick movement followed by a period during which substantially constant pressure is maintained.

The aim of the present invention is to provide an apparatus of this character having further various features of novelty and advantage.

More particularly, an aim of the invention is to provide an improved arrangement wherein the l apparatus may be very quickly and easily adjusted, the setting being so simple that errors due to carelessness" or ignorance on the part of the operator are substantially avoided. To this end, I provide an arrangement wherein there is no necessity of separately setting the relief valve for the system, the pressure with which that valve operates being automatically controlled by the setting of the pressure retaining valve which controls the flow of liquid from the pump pressure side to the accumulator pressure side.

A further aim of the invention is to provide an arrangement by means of which the system is automatically drained when the apparatus is shut down so that, when the apparatus. is again put into operation, the proper amount of elastic viiuid, such as air, will'be present in the accumulator.

A further object of the invention is to provide\an improved system or apparatus for eiectively operating or controlling a plurality' of actuated devices or instrumentalities. In accordance with the present invention, the arrangement is such that the actuation of one vof the actuated devices will not aect or interfere with the operation of one or'mo're of the other devices.

Another feature of the invention resides-in an arrangement whereby the pressure may be changed during the normal operation of the apparatus and in timed relation to the actuated instrumentality or instrumentalities. I

Other objects will be' in part obvious, and in part lpcintedout more `in detail hereinafter.

plified in the construction hereinafter set forth and the scope of the application of which will be indicated n the appended claims.

In the accompanying drawings wherein is shown, for illustrative purposes, one of the many a corporation of (Jon- 1931, Serial No. 511,950 (Cl. 10S-42) embodiments which the present invention may take,

Fig. 1 is a sectional view showing my improved system or apparatus more or less diagrammatically, in combination with a single instrumentallty or member to be actuated;

Fig. 2 is a view\similar to Fig. 1 but showing the arrangement associated with ay plurality of instrumentalities or devices to be actuated;

Fig. 3 is a sectional view taken substantially on line 3 3 of Fig. 5 and showing the arrangement disclosed in Fig. 2 embodied in a commercial or practical construction;

Fig. 4 is a side view of what is shwn in Figli; Fig. 5 is a sectional view taken on line 5-5 of Fig. 4;

Fig. 6 is a sectional View taken on line 5 5 of Fig. 4:;

Fig. 'l is aview taken on line 'l--l of Fig. 4 and shows` the body section in which the check valves are located; and

Fig. 8 is a View showing the pressure retaining valve operatively associated with a valve which be described. This arrangement is generally sim-'n ilar to that disclosed in my said co-pending application, the main differences residing in the construction and arrangement of the pressure retaining valve and the relief valve. It will be understood that the apparatus may be positioned in a tank or reservoir containing a suitable liquid, such a tank being shown in Fig. 2 and being designated by the numeral I0. The numeral II designates a pump of any suitable construction having an inlet I2 and an outlet delivering to a chamber or conned lspace designated generally by the numeral I3. Leading from this confined space is a passage I4 which in eiect formswith .the chamber I3 a single chamber .or conned space. This passage I4 leads to the actuated mechanism which is here shown for illustrative purposes as comprising a piston IS located vwithin. a cylinder I1. Associated with this cylinder may be a work-holding chuck, the head of a ram, or

- other device to be actuated, all as described more fully in my saidco-pending application. I8 designates a discharge pipe leading back to the tank. At the juncture of the passage III, the cylthe piston, and communication between the cylinder and the discharge pipe I8 when the valve is in another position, so as to permit the uid behind the piston, after the piston has been actuated, to flow through the discharge pipe. In the present instance, this valve is of the rotary type and it has a port 20. A spring or other suitable mechanism (not shown) may be employed for normally urging the piston to its normal or retracted position; that is to say, towards the right, referring toFig. 1.

The numeral 25 designatesa variable vpressure accumulator in open communication with a conned space or chamber designated generally by the numeral 26. The pump pressure chamber I3 is adapted to communicate with the variable pressure chamber through a port or by-pass 21 which is controlled by a retaining valve. The retaining valve includes a sliding head 28, the forward end of which is preferably tapered, as at 29. Behind this valve is a spring 30 backed up by an adjustable screw 3|. This spring normally urges the valve towards its closed position.

The numeral 35 ldesignates a relief valve which controls communication from the accumulator to the reservoir or tank I0.. This valve is so 1o-` cated as to contr'ol the exhaust port 36 leading from the variable pressure chamber 26. In the present instance, this valve 3 5 is a differential one, it having at one end a surface 31 against which the variable pressure is adapted' to bear, and having at its other end a smaller surface 38 against which the pump pressure is adapted4 to bear. As the surface 38 is smaller than the surface 31, it will be apparent that the pressure within the variable pressure Ichamber 26 will be less than the pressure' inthe pump pressure chamber I3. Communication between the variable pressure chamber 26 and the passage I4 is had through a port 40 which is controlled by a check valve 4 I, as in my said application.

The operation of the mechanism so far described is similar to the operation of the structure shown in my said application, and which operation is fully explained' in that application and, therefore, need notbe repeated here.

adjusting the mechanism, through ignorance or carelessness on the part of the operator, is guarded against. By/way of example, it may' be assumed that the valve 28 isset so as to maintain a pressure of 100 pounds on the pump pressure side and that the relative areas of the surfaces 38 and 31 are in a ratio of 4 to 5. Under this assumption, pressure within the accumulator may bebuilt up to pounds and up to that point the pump pressure acting on the surface 38 wll1 maintain the relief valve in closed position; that is, in a position where the port 36 is blanked. When the pressure on the accumulator side goes above 80 pounds, the aggregate pressure against the face 31 of the reliefvalve is greater than that 70- against the surface 38 so that the valve 3 5 is moved to open position, thus permitting the excess uid to vow through the exhaust port Abacl; into the tank.

Referring again to the pressure retaining valve,

the construction of the same is such as to p ermit of automatic draining of the systemL when the system is shut down. This is of Vadvantage, Vas it .has been found that if the fluid is maintained in the system, the air, within the air bell, may be partially dissipated so that when the system is again set into operation it may not function properly. The valve 28 has an opening 32 which,v when the valve is in its completely closed position, is in registry with the port A21. The -port or opening 32 leads to the outer end of the valve, andthe chamber in which the coiled spring 30 is located has a waste opening 33. Now, when the system is closed down by shutting off the pump, the pressure in the system will fall so that the valve 28 will move to its full closed position; that is, as far as it can to the right, referring to Fig. 1. This position is-shown in Fig. 5. The variable pressure side is then open to the atmosphere through the opening 32 an'd the waste opening 33, so that the uid within the air bell will drain out, and the air bell will fill with air. When the system is started up, the pump will build up a pressure on the pump side, and when said pressure reaches a predetermined point, say pounds, the valve 2`8'will open and the iluid will pass into the air bell, compressing that air. We

thus have a fresh supply of air off' the desired volume within the air bell.

Reference will now be had to the embodiment shown in Fig. 2 and' wherein a plurality of actuated devices. are operatively associated with the system so that thesedevices may be operated in anyorder or sequence desired, and the operation of one or more will not'materially affect or interfere with the operation of the others. In the embodiment'shown in Fig. 2, the parts correresponding to similar partsof Eig'. 1 bear corresponding reference numerals. In Fig. 2, there are a number of branch passages leading from the pump pressure chamber I 3f to independent actuated devices, each of which may comprise` a cylinder I1 and a piston I6 as in the preceding ernbodiment. Interposed in these branch passages.

are check vvalves 50, whichrespectively serve the same functions as the valve 4I of the preceding embodiment. Each of these valves is slidably mounted. in a .valve chamber 5I, each of which is open at one end to the variable pressure chamb er 26. Leading from the pump pressure chamber I3 to each valve chamber 5I is a restricted inlet port or passage 52. Also leading from an outlet port 54 of each valve/chamber 5I to a. l respective valve I9 is a branch passage 53. Each.

of the valves 50 is recessed at its outer end, as l at 54', and has a transverse opening 55 communicating with the recess 54' and also adapted to communicate with the' port 54 when the valve is closed. The outer end of each valve chamber 5I is closed by a screw plug 55 against which abuts Va coil spring 51, one end of which is bottomed' in the recess of the valve 50. The pressure of the springs may be suitably adjusted, as by the plugs 56. 'I'he valve 50 may be of such length that when it is in normal position, the outer end of the same is just short of the inlet port 52. `When the valve is in normal or closed position, the passage 53 is in open communication with the chamber I3 through the recess-,54' in the valve and the cross opening 55 thereof.-V

The' operation of this arrangement is briey 70 valve I9 is .initially opened, the .pump pressure in front of the valve will drop slightly and -momentarily to a point below the variable pressure on the rear end of the valve. During the forward movement of the valve the restricted port 52 is blanked oif and communication is established directly between they variable pressure chamber 26 and the passage 53. The second valve 50 from the top of Fig. 2 is shown in a position where the port 52 is blanked off. When the variable pressure drops below a predetermined limit, the spring 51 will return the valve to normal position, thus closing off the variable pressure and permitting the pump pressure to become effective through restricted port 52 to slowly move or hold theactuated device, as shown in connection with the third valve from the top of Fig. 2. It will be apparent that since the port 52 is restricted and in addition that the valve 56 blocks off pump pressure when the associated actuated device is being acted upon by the variable pressure of the accumulator, the pump pressure Will be'maintained in the pump chamber I3 s-o that, if it is desired to actuate or hold one or more of the other actuated devices, the pump pressure on that device will not be affected; for example, in Fig. 2 the actuated device associated with the third valve from the topis shown as being moved slowly by the pump pressure. Now when the valve I9 associated with the second valve 59 is turned to -open position, the valve B will.prevent communication between the second cylinder I1 and the pump pressurechamber I3 so long as the variable pressure is moving the second piston I6 on the quick portion of its stroke, and therefore pump pressure on the actuated device associated with the third valve Will not be decreased or changed.

Reference will now be had to Figs. 3 to 1, inclus'ive, and which gures show the arrangement of Fig. 2 embodied in a practical and commercial structure. closure is by way of illustration. This mechanism includes Va body portion formed of two castings 66 and 6I secured together by bolts 62. The casting 66 has a bore 63 to which is secured the pipe 64 leading to the` accumulator. Extending transversely of the bore 63 is a bore 65 having an enlarged portion 66 at its right-hand end. The enlarged portion 66 has an exhaust port 36 and is connected to the bore 63 by an yopening 61. Leading to the bo're 65 is a bore {iB-which is connected to a pipe 69 leading from the pump. 'Ihe relief valve 35 and the pressure retaining valve 28 are located in the bore 65. The casting 6I has four Q sleeve-likel portions or guides 58 constituting valve chambers 5I in which are respectively mounted check valves 50. Each sleeve portion 58 has an internal annular groove 59 adjacent theouter end of the valve when the latter is closed. At the juncture of the valve chambers 5I is a space to which leads an axially disposed bushing 1I. which communicates with the bore 63 ofthe casting 60. Leading from the respective -chambers 5I are pipes 13, the bores of which cor- It is, of course, obvious that this disreferehce characters corresponding to the reference characters for like parts in Figs. 1 and 2, and

need not be further described. 'I'he operation of the mechanism shown in Figs. 3 to 7 is identical to that described in connection with Fig. 2 andA need not again be reviewed. It is observed that the opening in the pipe 69, the bore 68, theport y 11, and the annular groove taken together correspond to the pump pressure chamber I3 of Fig. 2. The bore 63, the opening through the sleeve 1I, and the space 10 constitute a variable pressure chamber corresponding to the chamber 26. The bores of the pipes 13 correspond to the passages 53.

Reference-will now be had to the construction `shown in Fig. 8 and wherein the pressure retaining valve of the system is operatively associated -with the controlling valve for the actuatedmechanism in such manner that when this controlling valve `is operated beyond a predetermined point, the setting of the retaining valve is automatically changed. Only a por-tion of the system is i1- lustrated, as it is understood that the arrangeinent may be associated either with the mechanism described in Fig. l or in Fig. 2. The controlling valve, as shown in Fig. 8, is to take place of the controlling valves 'I9 in Fig. 1 or one of such valves in Fig. 2. Controlling valves of this type may vbe substituted for all of the valves I9 in Fig. 2. 1

yReferring to Fig. 8`more specifically, the retaining valve 28 may beof the same construction as that shown in the v.preceding figures, except that behind the spring 3| is a plunger 80 adapted to slide in a hollow nut 8 I. The controlling valve may be of any suitable kind, but it is here shown as including a casing 82 xed `to a bracket 83 which in turn is fixed to a suitable support (not shown). The casing 82 has an inlet opening 84 to which leads a pipe 85. This pipe leads` from the pump pressure side and may be considered as being the passage I4 ofFig. 1 or one of the branch passages 53 of Fig. 2. The casing 82 has an outlet port to which is connected a.pipe 81 which leads to a device tobe actuated and which is not shown. This actuated device may be a brake cylinder, -such as provided on automobiles having hydraulic brakes. The opening through the pipe 81 may be considered 'as the equivalent of the cylinder I1 of the preceding embodiments.. The valve casing has a lining or sleeve 88 having a plurality of spirally arranged openings 89 communicating with the inlet opening or passage 84. It also has an outlet port 9 registering with the pipe 81. The valve is in the form of a plunger or reciprocating bar havi/ng a body portion 6I', a stem 92, and a head 93, the -body portion and head closely but slidably tting in the sleeve. Leading from the valve casing is an exhaust opening or port 94 which corresponds to the pipes `I8 of the preceding embodiment. Journaled in the bracket 83 is a pin or shaft 91 to which is fixed an arrn.98 having a shoulder adapted to abut against' the outer end of the plunger 80. Also xed to this shaft 91 is an arm 99 having on its lower end an anti-friction roller IDH operating in a vertical groove IUI in' the valve 9 I. The numeral I 02 designates a handle fixed to the pin 91 for rocking the lever which is composed of arms 98 and 99.

The operation of the construction shown in Fig. 8 is briefly as follows, it being assumed that the controlling Valve is associated with a brake mechanism. 'Ihis assumption is by way of exemplication only. When the parts are in the CIIv sired, the valve 9| normal position, that is, when no pressure is desired inthe brake cylinder, the lever |02 is in the dotted line position and the valve 9| is in its extreme right-hand position so that openings or ports 89 are closed by the body portion 9| of the valve and communication is established between the pipe 81 and the exhaust 94 through the space about the stern 92. When it is desired to apply the brakes, the lever is raised, thereby moving the valve 9| to the left and when this is done, the exhaust port is closed olf and the open ings 89 are uncoveredv in sequence. It will be observed that when the valve 9| is in full closed position there is a space between the arm 98 Yand the plunger 80 so that during a predetermined portion of the opening movement of the valve 9| the setting of the pressure retaining valve 28 is not affected, and during this time service application of the brakes is had. If a slight braking action is desired, the valve 9| is moved to a position where only a few of the openings 89 are uncovered, andwhen a greater pressure is desired the valve is further opened. When the controlling valve 9| is opened, the accumulator pressure is first effective in quickly moving the cylinder to which the pipe 81 leads,- and then the pump pressure comes into play to slowly move thecylinder and hold it in actuated position. When emergency application of the brakes is deis rapidly moved tol the full open position shown in Fig. 8, and when this is done the arm 98 moves the retaining valve to closed or partially closed position. When the valve 9| is first opened, the accumulator pressure will quickly bump the cylinder to which the pipe 81 leads and then the pump pressure comes into play, as in the case of a service application. But in oase of emergency application, a higher pressure than that normally maintained on the pump side is set up on that side because the pres-- sure retaining valve has been closed, or partially closed. As soon as the pressure on the pump side is increased, this increase is immediately eective on the cylinder because the passages leading to the cylinder are completely lled with liquid which is substantially not compressible.

' As many changes could be made in the above construction and many apparently Widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the following claims is intended to cover all of the generic and specific features of the inventionherein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. In an apparatus of the character described,

a pump pressure chamber or passage, a pump for delivering liquid under pressure to said chamber, a variable accumulator, a .port between said chamber and accumulator and through which said accumulator receives the liquid from said chamber, a port between said accumulator `and chamberI and through which said accumulatoris adapted to discharge into ,said-chamber, a pressure retaining valve for preventing liquid from flowing through said first mentioned port until a predetermined pressureis built upon the pump Y :essure side, means for closing said second mentioned port while the 'pressure on the pump pressure side is above that of the accumulator pressure side, an exhaust port for the system,

and a relief valve forcontrolling said exhaust port and arranged to be moved to closed position by pressure on the pump pressure side and to be moved to open position by ,pressure on the accumulator side. l

2. In an apparatus ofthe character described,

a chamber or passage, variable pressure means, l

means for delivering iluid under pressure to said chamber and said variable pressure means, a pressure retaining valve for preventing fluid from flowing into said variable pressure means until a predetermined pressure is built up in said chamber by said uid delivering means, and means for establishing communication from said variable vpressure means to said chamber when the pressure in said chamber falls below that of Vsaid variable pressure means, said retaining valve including means for automatically draining said variable pressure means of fluid when the apf paratus is shut down.

3. In an apparatus of the character described, a chamber or passage, a variable pressure accumulator, a pump' for delivering uid under pressure to said chamber, a pressure retaining valve for preventing fluid from flowing into said accumulator untill a predetermined pressure is built up in said chamber `by said pump, and means for establishing communication from said accumulator to said chamber when the pressure in said chamber falls below that of said accumulator, said retaining valve including a valve head and a spring normally urging said head to closed position, said head having an opening normally outof communication with said accumulator and said head being moved to a position where saidv opening is in communication with said accumulator when the system is shut down whereby said accumulator may drain through said opening.

4. In an apparatus of the character described, a chamber, a pump for delivering liquid under pressure to said chamber, a variable accumulator, a pressure retaining valve for preventing `uid from flowing into said accumulator until a predetermined pressure is built up in said chamber by said pump, a plurality of passages adapted to be respectively associated with devices to be actuated, and a plurality of check valves, one for each passage, each check valve in one position establishing communication between said chamber and the respective passage and in another position establishing communication between the accumulator and the respective passage, each check valve being moved to the latter position when the pressure normally tending to move the valve to the first position becomes less than the accumulator pressure.

5. In an apparatus of the character described, a chamber, a variable pressure accumulator, a pump for delivering fluid under pressure to said chamber and said accumulator, a pressure retaining valve for preventing fluid from`flowing in to -said accumulator until va predetermined pressure is' built up in said chamber by said pump, a plurality of passages adapted '/to lead to drespective actuated devices and eachA adapted to communicate with said chamber and accumulator, a check valve for each passage, and means .for normally urging each check'valve to a posia chamber, a variable accumulator, a pump for delivering liquid under pressure to saidlchamber L'ns .accumulator respectively.

7. In an apparatus of the character described, a chamber, a variable accumulator, a pump for delivering liquid under pressure to said chamber and accumulator, a retaining valve for preventing liquid from owing into said accumulator until a predetermined pressure is built upv vin said chamber by said pump, a plurality of passages each adapted to communicate with the chamber and the accumulator, and a plurality of valves one for each passage and normally urged to a closed position for preventing .communication between the accumulator and the respective passage, each of usaid valves being arranged to establish communication between the chamber and the respective passage when the valve is in closed position, the pressure on the accumulator side normally tending toL urge said valve to an open position, each valve being so arranged that when in open position'it closes off communication between said chamber and the respective passaget 8. In an apparatus ci the character described( a chamber, a variablefccumulator, a pump for delivering liquid under pressure to said chamber and accumulator, means for preventing liquid from owingI into said accumulator until a -predetermined pressure is built up in said chamber by said pump, a Aplurality of individual valve mechanisms each having a valve chamber communicating with said accumulator and said chamber and each having an outlet passage, a check valve in each valve chamber, means associated with each check valve for urging the same to a closed position where communication between the accumulator and the respective pas-l sage is prevented and communication is had between the first chamber and said passage, said valve being constructed to prevent communication between the rst chamber and said valve chamber when the valve is in open position.

9. In an apparatus of the character described, a chamber, a variable accumulator, a pump for delivering liquid under pressure to said chamber and accumulator, a pressure retaining valve for f preventing liquid from ilowing into said accumuand said accumulator, a plurality of valves one t 10. In an apparatus of the character described,-

a chamber, a variable accumulator, a pump for deliveringvliquid under pressure to said chamber and accumulator, a pressure retaining valve for preventing liquid Afrom iiowing into said accumulator until `a predetermined pressure is built up in said chamber by said pump, a plurality of passages adapted to communicate with said chamber and said accumulator, a pluralityof check i valves, one for each. passage, means normally urging each check valve to Aclosed position where communication between the accumulator and the respective passage is shut oi and communication between the chamber and the respective passage is established, the pressure in said chamber acting on said valve when in closed position in opposition to the pressure of the accumulator on said valve, the pressure of the chamber on said valve being discontinued when the pressure of said accumulator has moved the valve to` open position and in which position communication is established between the accumulator and the passage.

l1. In an `apparatus of the character described, a chamber, a-variable accumulator, a pump for delivering liquid under lpressure to said chamber and accumulator, a pressure retaining valve for preventing liquid lfrom owing into said accumulator until a predetermined pressure is built up in said chamber by saidpump, a plurality of individual valve mechanisms, each having a valve chamber provided with an opening communicating with the accumulator, an inlet. port compassage between said opening and port, a checkA valve in each Valve chamber, a spring associated 'with each check; valve for urging the same to closed position where said opening is closed, each valve when in closed position being subjected to accumulator pressure and the pressure of said chamber in opposition and communication being established between the chamber and said outlet passage, each valve when in open position blanking said inlet port and establishing communication between said 'accumulator and the respective outlet passage.

12. In an apparatus of the character described, a chamber, a variable pressurel accumulator, continuously operating means for delivering liquid under pressure to said chamber and saidaccumulator, an adjustable pressure retaining valve for preventing liquid from iiowing into said accumulator until predetermined pressures are built up in said chamber by saidcontinuously operating means, a controlling valve for controlling the discharge of liquid from said chamber, and an operative connection between said controlling valve and said pressure retaining valve,- whereby the setting of lthe latter is automatically changed after the controlling valve is operated beyond a predetermined point.

13. In an apparatus of the character described, a chamber, -a variable accumulator, a pump for delivering liquid underpressure to said chamber and accumulator, a pressure retainingvalve for preventing liquid from flowing into said accumulator until predetermined pressures are built up in said chamber by said pump, a controlling valve for controlling, the discharge of liquid from said chamber at varying rates depending upon the extent to which the controlling valve is opened, and means for operating said controlling valve and also for changing the setting of said pressure retaining valve. during at least a portion of the operating strokeof said controlling valve.

14. In an apparatus of the character described, a chamber, a variable accumulator, a pump for delivering liquid under pressure to said chamber and accumulator, an adjustable pressure retaining valve for preventing liquid from flowing into said accumulator until predetermined pressures are built up in said chamber by said pump, a controlling valve for controlling the discharge of 'liquid from said chamber and accumulator at varying rates, means for operating said controlling valve, and means between said operating means and said pressure retaining, valve for changing the setting vof the latter after said controlling valve has been moved to a predetermined extent.

15. In an apparatus of the character described, a chamber, a variable accumulator, a pump for delivering liquid under pressure to said chamber and accumulator; a pressure retaining valve for preventing liquid from iiowing into said accumulator until a predetermined pressure is built up in said chamber, said valve having a member, a spring normally urging the member to closed position, and a plunger behind the spring; a controlling valve for controlling the discharge of liquid from said chamber and accumulator and .having a valve. chamber provided lwith a plurality of openings .dapted to be opened in sequence and a valve head controlling `said openings, and means for simultaneously moving said valve head and said plunger after the valve head has been moved to aA predetermined extent.

16. In an apparatus of the character described, a chamber, variablepressure means, means for delivering iiuid under pressure to' said chamber and said variable pressure means, adjustable means for preventing fluid from flowing into said variable pressure means until a predetermined pressure is built up in said chamber by said uid delivering means, means for establishing com- Y .munication from said variable pressure means to said chamber when the pressure in said chamber falls below that of said variable pressurey means, and a relief valve for the system and arranged to be moved to closed position by pressure acting directly on said valve on the pump pressure side and to be moved to open position by pressure acting directly on said valve on the accumulator side, the operation of said relief valve automatically varying. in accordance with the setting of said adjustable means.

\1'7. In an apparatus of the character described, a chamber or passage, a variable pressure accumulator, continuously operating means for delivering fluid `under pressure to said chamber and said accumulator, a pressure retaining valve for preventing duid from flowing into said accumu.

lator until a predetermined pressure is built up in said chamber' by said continuously operating means, means for establishing communication from said accumulator-to saidy chamber when the pressure in said chamber falls below that of said accumulator, and a relief valve for the system .and arranged to be moved to closed position by pressure acting directly on said valve on the pump pressure side and to be moved to open position b y pressure acting directly von said valve on the accumulator side, the operation of said relief valve being controlled by the ratio of pressures exerted against said relief valve on the pump lpressure and accumulator sides thereof.

18. In an vapparatus of the character described, a pressure chamber or passage, a pump for de- .livering fluid to said chamber, an accumulator,

a pressure retaining valve between said accumulator and chamber for maintaining a predetermined pressure in said chamber and including a valve head, a spring normally urging the valve into closed position, and means for adjusting the spring; a check valve between said chamber and accumulator and opened by'- the pressure of the accumulator, and a differential relief valve for the system and including a member arranged to be moved to closed position by pressure acting directly on said member on the pump pressure side and to be moved to open position by pressure acting directly on said member on the accumulator side.

19. In an apparatus of the character indicated, a pump device, an accumulator device connected thereto to be charged thereby, and means for discharging an excess of uid from one of said devices, said means including a relief port and diierential valve means `for controlling said port, said differential valve means being open to accumulator pressure at one side to tend to open said port and being open to pump pressure at the other side to tend to close said port.

20. In an apparatus of the character indicated, a pump, an accumulator connected thereto to be charged thereby, means for preventing a flow of fluid from said pump to said accumulator until a predetermined pressure is built up by said pump, and means controlled by the differential of pump and accumulator pressures for maintaining the ratio of maximum pump and accummaximum pump and accumulator pressures.

22. In an apparatus of the character indicated, a pump, an accumulator connected thereto to be charged thereby, a plurality of iluid pressure actuated devices, and means for subjecting one of said devices to pump pressure and accumulator pressure at diierent times while subjection another of said devices to pump pressure alone, said means including restricted passage means to prevent a rapid flow of pump pressure fluid to said one of said devices, whereby pump pressure will not be substantially lowered on said another actuated device.

23. In an apparatus of the character indicated, a pump, an accumulator connected thereto to be charged thereby, means for draining theaccumulator comprising valve and port means, said valve being open to pump pressure to hold said valve in port closed position, and means for urging sol said valve to port open position whereby upon failure of -pump pressure said accumulator will be drained. y

DONALD H. MONTGOMERY.

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