US2401845A - Hydraulic accumulator - Google Patents

Description

June 1 l, 1946;

W. T. STEPHENS HYDRAULIC ACCUMULATOR Filed May 20, 1943 3 Sheets-Sheet l 1 Qi. 22 b 26 TANK 1 74 2 12 P i v l 25 1.2 1.3? rm? L1? ll- EQCUMULFSTOR 16 MJM Patented June ll, 1946 HYDRAULIC ACCUMULATOR William T. Stephens, Cleveland, Ohio, assignor to Engineering Company,

Cleveland, Ohio, a corporation of Ohio Application May 20, 1943, Serial No. 487,777

Hydraulic Control 19 Claims.

This invention relates to hydraulic accumulators.

More particularly the invention relates to high pressure accumulators which incorporate automatic excess pressure relief and low pressure bypass for the source of high pressure liquid when the accumulator is charged.

It is a general object of the present invention to provide a novel and improved accumulator for hydraulic systems. 1

More particularly it is an object of the invention to provide a hydraulic accumulator in combination with a pressurerelief valve arranged and adjusted to cause by-passing of liquid from the pump to low pressure upon the completion of charging of the accumulator. i

One of the important objects of the invention resides in the use of the accumulator plunger as a valving means to control the operation of the by-pass valve under the action of fluid discharged by the relief valve.

Another important object of the invention consists in the provision of a hydraulic system including a power pump and accumulator with combined relief and by-pass valves and a manual pump permitting operation in the event of failure of the power pump.

It is an important feature of the invention to provide a hydraulic accumulator with one or more plungers mounted in a housing having a chamber adapted for connection to a. high pressure source of supply, a chamber'for connection to a liquid sump and a chamber for connection to a motor control valve, in which the accumulator plunger is exposed to the liquid in the last mentioned chamber, together with a by-pass valve between the first and second chambers adapted to be opened when pressure in the first chamber becomes excessive.

A further important feature of the invention resides in the combination of a by-pass valve, a relief valve and an accumulator plunger valve so associated in a hydraulic circuit that pressure in excess of that necessary to charge the accumulator opens the relief valve and provides operating fluid for actuating the by-pass valve which is then locked in open position until the accumulator is discharged whereupon it returns to its normal closed position.

Another important feature of the invention consists in the provision of an accumulator having a plurality of plungers or pistons only one of which acts in a valve capacity to control the operation of a by-pass valve.

Other and further features and objects of the invention will be more apparent to those skilled in the art upon a consideration of the accompanying drawings and following specification wherein are disclosed several exemplary embodiinents of the invention with the understanding that such modifications thereof and combinations of the same may be made as fall within the scope of the appended claims without departing from the spirit of the invention.

In said' drawings:

Fig. l is a schematic and diagrammatic illustration of a hydraulic system and circuit incorporating the invention of this application;

Fi 2 is a longitudinal section through one form of hydraulic accumulator constructed according to the present invention and taken on line 2-2 of Fig. 4;

Fig. 3 is a longitudinal section at right angles to Fig. 2 and taken on line 33 of Fig. 4;

Fig. 4 is an end elevation of the embodiment of the device illustrated in Figs. 2 and 3;

Fig. 5 is a longitudinal section of a modified form of hydraulic accumulator taken on line 5-5 of Fig. 6; and

Fig. 6 is an end elevation of this embodiment.

In systems where the hydraulic operation and/or control of various devices such as hoists, rams; hydraulic motors and the like is used for the manipulation of machinery or tools there is usually only an intermittent demand for the delivery of high pressure liquid for actuating the motors or the like. When this demand does occur, however, it is usually desirable that a considerable quantity of liquid be delivered at a relatively high rate without substantial reduction in pressure. If sufficient pump capacity is provided for this purpose the initial cost of the installation is excessive and the power consumed for driving the pump is too great. As an alternative it has been suggested that a, much lower capacity pump be used together with a hydraulic accumulator which usually takes the form of a spring or Weight loaded plunger o'r piston which can be charged by a relatively small capacity pump Working over a considerable period of time, particularly the idle period for the motor or other hydraulic device 'used for supplying power. Thus when fiuid delivery is required it -can be taken both from the accumulator andv Pump.

Pumps for delivering hydraulic fluid are usually of the positive displacement type capable of delivering fluid against high pressures but they cannot stand a complete stoppage of flow from the delivery side without being harmed. When they are connected to any type of hydraulic system some means must be provided to relieve or by-pass-the liquid when the pressure becomes excessive. Such means usually comprises a simple spring-loaded relief valve.

In accordance with the present invention the functions of a hydraulic accumulator are combined with those of pressure relief means but by a novel arrangement of parts, instead of providing relief for the pump'at the maximum pressure required for charging the accumulator, the

pump is relieved or lay-passed at nearly zero pressure while the accumulator is retained in its charged condition ready instantly to deliver a large quantity of high'pressure liquid to the power source requiring the use of the same. The construction of the valve mechanism associated with the accumulator is such that. upon partial discharge of the accumulator the pump is again associated with the high pressure side of the accumulator and delivers any additional quantity of liquid, at the high pressure needed, beyond the capacity of the accumulator. The pump is also at the same time connected to recharge the accumulator when the demand for high pressure liquid ceases.

Referring now to the drawings for a better understanding of the invention and first to Fig. 1 for an illustrative embodiment of a circuit'for taking advantage of the present invention, there is shown at ill any suitable form of positive displacement mechanically driven liquid pump which receives liquid from a reservoir, tank or sump [2 through intake pipe hi and delivers the same through pipe to the accumulator-valve combination of the present invention generally represented at is. The high pre sure side of the accumulator delivers to a pipe l8 while the by-pass or relief side discharges through pipe back to the tank.

At 22 is shown the plunger of a hydraulic ram of the single acting type which will be assumed as the high pressure liquid requiring element or motor in the system. The delivery of high pressure fluid to and the discharge of the fluid from this motor is under the control of a manually operable valve 2% which may be of conventional type. This valve is connected by pipe 25 to the high pressure line l8 and when adjusted from neutral to one operative position permits the delivery of high pressure fiuid beneath the plunger of the ram for moving the same against a load. When the valve is positioned in another of its operative positions the source of high pressure is cut off from the ram and the chamber beneath its plunger is connected to the return pipe 26 which leads to low pressure pipe line 2? leading to the'tank so that the ram may return to inoperative position under the action of its load. Obviously a double acting ram may be used in a manner well understood in the art. It will be clear that any numberof hydraulic motors and, their associated control valves may be connected 7 in parallel or shunt across the high pressure and low pressure pipe lines l8 and 2! and each can be operated independent of the other or two or more may be operated in unison in either direction.

One form of accumulator i6 is illustrated in Figs. 2, 3 and 4. It includes a main casing or housing 36 in the form of a roughly cylindrical casting, a cap ill at the left end and a cap 32 at the right hand end. The main casing has its left and right hand ends finished flat and smooth as at 3 3 and 35 and a number of openings extend through these ends for communication with the respective chambers 38 and M2 formed in the are rigidly secured to the housing by studs-ll best seen in Fig. 4. Ground fits may be used at the junctions of the caps 'and body or appropriate gaskets applied as seems desirable.

The body of the accumulator housing is longitudinally drilled to provide a plurality of passages extending from end to end of the same. For the sake of convenience in manufacture these are preferably of uniform diameter and appropriately spaced to provide adequate strength of metal between them. Any suitable number of these passages is provided but at least two, as shown at 44 and 55, are necessary. The third one shown at 46 is optional while any desired duplication of passage 86, to increase the capacity of the accumulator, may be effected in accordance with the demands of the system into which it is to be connected.

The casting formingthe body 30 of the housing is cored to provide a high pressure chamber 56 having anentrance port 5i for connection to the high pressure side of the pump. This chamber extends longitudinally of the, housing and joins the transverse passages 52 and 53 which extend up and intersect the bore near its ends. Between passage 52 and the chamber 38 in the left hand cap, which is provided with an outlet port 54 for connection to the mootr control valve or to the so-called high pressure line, there is arranged a check valve 55 taking the form of a .tube 56 open on the inner end and closed at the outer end by a cap 57 the flanged extension of which bears on the end 34 of the housing. This hollow tube has its inner end open to the chamber 52 and is provided with radial bores 58 closed by the walls of the cylinder 65, in which it is slidably mounted, when in the position shown where it is held by a light spring 59. This assemblage constitutes a check valve operating at very low pressure to open communication between the high pressure chamber 50 and the chamber 38 v but quickly closing when the relative pressure conditions change so that pressure in 38 is higher than in 50.

The passage or cylinder M which houses the bore 6! in the collar or plug 62 closing the end.

of M and longitudinally drilled to accommodate the reduced end 63 of the accumulator plunger. This end normally bears against the under surface of the cap 3! as shown, under the action of the strong helical spring 65 partially housed within the hollow main portion 65 of the accumulator plunger and having its far end received in a recess 6'1 in the cap 32. The rate and strength of spring 65 is predetermined in accordance with the diameter of the pin 53 constituting the effective area of the hydraulic plunger and the desired operating pressure of the liquid distributed from the accumulator.

It will be seen that the rear end of the accumulator cylinder opens into an enlargement m in full communication with the chamber til in the right hand cap, which chamber is adapted for connection through port H with the sump or tank for reserve liquid. In order that no liquid may be trapped betweenthe enlargement of the accumulator plunger and the back of the collar 62 to prevent return of the accumulator, the tapered head thereof is drilled as at H to permit any leakage to return to the sump in an obvious manner,

A by=pass valve i5 is arranged with a working plunger.

- W and 40 and back to the reservoir.

a leases fit in the right hand end of the bore 55 and normally close off communication between the high ressiue chamber and the low pressure chamer ill. Valve iii is a spool valve having the lands and if at opposite ends thereof and the reduced central portion In the position illustrated the reduced portion if. is in communication with the extension of the high pressure chamber 53 while the land ll closes off the right hand end of the bore '55; and also the lateral passage 9i: extending from the'enlargement lb in which the end of the accumulator plunger operates. The valve is normally maintained in the position illustrated by a light helical spring 85, the left end of which is housed in a recess in the valve and the right end of which bears against the cap It will be noted that this valve is balanced and that no amount of pressure in the chamber 5% acting on the reduced diameter of the same will move it to permit escape of high pressure liquid to the sump and therefore some mean is necessary to initiate the operation of this valve.

This means comprises a relief valve 85! coaxial with valve l5 and comprising a hollow plunger having a pointed end 66 adapted to cooperate with a valve seat in a drilled plug El closing off the bore 5 to the right of the extension 52 of the high pressure chamber. The area of the central opening in the plug 8i which is closed by the plunger 8 is adjusted in accordance with the strength of helical spring 88 which normally holds the relief valve 8 3 closed so that the valve is opened when the pressure in chamber 50'is greater than that necessary to load lator plunger.

The spring 88 is partially housed in the hollow valve and acts against an abutment sleeve 98 threaded in the bore 65 just to the left of the valve 15. This abutment forms the stop to limit movement of valve toward the left and is perforated as at 9! 'to permit the flow of oil through the plug 81 and the bores 92 in the relief valve 84 to act on the piston-like end of the by-pass valve.

The lands 16 on the left end of the by-pass valve have a minimum lap 94 when the valve is closed, cutting off the high pressure chamber 53 from a chamber 95 surrounding the end of the by-pass valve and in which the head of the abutment 90 fits. This chamber 95 is connected by passage 96 to a chamber intermediate the ends of the bore 44 housing the accumulator In its uncharged position the accumulator plunger provides radial bores 91 which register with the passage 96 and hence permit the flow of fluid from the same into the hollow of the accumulator plunger and to the chambers It will be seen therefore that with the accumulator plunger in the position shown any fluid attempting to operate on the piston-like end of the by-pass Valve can only be at reservoir pressure which is insufiicient to overcome the by-pass valve spring M.

In normal operation with the accumulator connected as shown in Fig. 1, when the pump is started pressure is built-up in high pressure chamber 5%. All parts are initially in the position shown in Fig 2. As soon as thi pressure becomes sufficiently high the check valve 55 is moved to the left and oil issues through the port 58 therein into chamber 38 and acts on the end of the pin $3 of the accumulator plunger. As I the pressure builds up the accumulator fluid passes in through the relief valve and the iii the accumuport iii, in the spring abutment for the same, and acts on the piston-like end of the by-pass valve l5. This high pressure fluid is not vented to the sump since the ports QE in the accumulator plunger are now out of register with passage to which latter is therefore closedoff. The high pressure oil therefore forcesthe'. by-pass valve to the right so that the reduced diameter i8 spans the passages 53-43% and permits the high pressure from the pump to be discharged into chamber lu and back to the reservoir against no resistance except that of the pipe lines.

When the valve 75 reaches an open position, pressure is immediately reduced in chamber 50 and the relief valve 85 promptly closes under the action of its relatively strong spring 88. This immediately traps a charge of oil behind the relief valve and the chamber to the left of the by-pass valve is now a fully closed compartment from which none can escape. This charge of oil holds the by-pass valve open for complete by-passing of the pump until such time as the charge in the accumulator piston chamber is released by operation of the motor control valve. During the Joy-pass operation the accumulator is maintained charged by the action of the check valve 55 since the pressure of its left end is high and that on its right'end low. If it is assumed now that the valve 24 'in Figure l is moved to permit the escape of some of the liquid under accumulator pressure, then the accumulator plunger, or plungers if a plurality have been used, will move toward the left and eventually the ports 91 will register with chamber 96 and the pent up quantity of oil which has been holding the bypass valve open will escape to sump chamber 40 and the by-pass valve will move to the position shown in Fig. 2 under the action of its return spring 8!. This permits the pump to again build up pressure in chamber 50 to repeat the cycle of charging the accumulator etc.

In the event of failure of the power pump for any reason whatever the operator should have available an auxiliary source of supply of high pressure oil at least to perform emergency operations of the hydraulic motor such as for instance lifting or lowering a load which may be only partially moved at the time of pump break down. For this purpose there is conveniently arranged in the housing of the hydraulic accumulator a manual plunger pump illustrated in Fig. 3. This pump operates in the cylinder or bore 46 which extends between the low pressure chamber 40,

which is normally filled with oil at sump pressure from the tank (which should be elevated above both the power pump and the accumulator), and the chamber 38 connected both to the accumulator piston and the control valve for the motor.

The foot valve for the pump is a ball IUD which under the action of helical spring I02 closes the discharge port Hi3. This valve operates in the counterbore Hit in a bushing 15 threaded into the left end of the cylinder 46 and having a head which compresses a packing against a face 35 of the housing, The spring is guided in the counterbore i0 8 and has its abutment against the cap 3i.

The pump plunger comprises a rod-like member I07 having a working fit in the bore Q6 and integral with a reduced diameter stem I08 which is passed through a suitable bored and bushed opening III) in a boss in the cap 32. The shoulder at the junction of the parts I01 and I08 prevents the pump plunger from being withdrawn or from being pressed outwardly under the 'action of its helical return spring II2 which has its left end abutted against the inner end of the bushing I05 and its right end partially housed in the large bore H5 in the lower end of the plunger. It abuts against. the shoulder I It at the junction of the bore. I I5 and the smaller bore I I8 in which the top valve ball I20 operates. This ball closes the inner end of a small longitudinal assage I2I which connects with cross bore I22 in the plunger near the shoulder. The cross bore is always in communication with the upper concentric chamber I25 which is extended into the main housing from 40 to insure availability of oil to the pump plunger at any portion of its out stroke.

The top valve ball I20 is urged against its seat at the mouth of the longitudinal passage I2I by a light helical spring I21 which is positioned and tensioned by means of the hollow threaded bushing I28, the opening through-which provides access for oil entering through I22, I2] andIl8 sothat it is delivered beneath the plunger and can then be forced out of the pump cylinder on the down stroke. The operation of the pump will be obvious for upon manipulation of the plunger by means of the hand knob I30, the pump collects its oil on the upstroke from the chamber 80 and on the downstroke delivers it into the chamber 38 where it may directly operate the motor mechanism or charge the one'or more accumulator plungers. Although when this pump is in use the relief and bypass valves Wand I5 are not available for operation because of the direct delivery into chamber 38 instead of into high pressure chamber 50, nevertheless no damage is likely to result since insufilcient pressure can be built up manually to be of any harm.

In the embodiment of Figs. 5 and 6 there is illustrated a multiple plunger type of hydraulic accumulator with associated relief and by-pass valves. The device shown is not equipped with a manual pump but if one is desired it can be substituted with no difficulty for one of the accumulator plungers.

In this construction there is a minimum of coring in the several castings. The various valve parts are much simpler in construction than in the first embodiment and the amount of machine work necessary for their construction is materially reduced.

In this embodiment the main housing is a simple cylindrical casting 200 which has extending from its arcuate surface a boss 20I containing the inlet or high pressure connection 202 from the pump and forming the'high pressure chamber 203. A plurality of straight bores or passages 204, 205 and 206 extend from-flat end 208 to fiat 5 end 209 of the part 200,

. The end caps 2H and 2I2 are identical and each is merely a shallow cup whose periphery fits in'a fluid tight manner against the corresponding fiat end of the main body portion. Each 4 cup is appropriately bossed and bored in alignment with bores 2I5 in the body to accommodate the through bolts 2I6 for holding the parts assembled. The cap 2i I has the port 2I8 for connection to the control valve while the cap 292 has the port 2 I 9 for connection to-the sump.

As seen in Fig. 6 there are a plurality of the bores 20% closely spaced throughout the areas of the ends of the body and each of these contains an accumulator plunger 220, in order to provide a large capacity without the use of ponderous.

springs. Each of the plungers is a simple rod hollowed from one end as 'at 22I to partially house its helical spring 222. The other end of the rod abuts against the cap 2I2 when the accumulator is unloaded. The left hand end of each plunger may be reduced as at 22 3 to form a stop for resting against the cap 2i I and to'permit access of the fluid to a sufiicient area for starting the compression of the spring.

The plunger in bore 205 is identical with that in the bores numbered 205, but this bore is connected by a short passage 226 to the chamber 221 surrounding the inner head of the by-pass valve. When the plunger in bore 205 is loaded its'skirt closes ofi the passage 226 for the same purpose as explained in connection with the first embodiment when the radial bores 01 are closed off from passage 96. The only diflerence'in operation is that a considerable loading is necessary in the embodiment of Fig. 5, beforethe passage 226 is cut ofi from the sump, whereas the corresponding passage is immediately cut ofi' in the arrangement of the first embodiment.

In the construction of Fig. 5 the check valve is much simplified comprising simply a rod 230 hollowed as at 23I at its inner end and provided with radial bores 232 which are normally housed in the cylinder 206 but which are opened, as shown, into the chamber in the head 2II to permit passage of oil from the high pressure chamber 203 thereto. The head ofthe rod 230 is rounded so that pressure may have'access thereto for closing the same when there is a. tendency toward reverse flow. No. spring is necessary.

An appropriate stop for the check valve is formed by the bushing 232 in the cylinder 20% against which the lower end of the check valve abuts when it is closed. The perforation in this bushing permits access of high pressure fluid to the simplified relief valve 235, which is merely a non-circular rod drilled to provide a hollow to receive the end of the compression spring 238 and pointed as at 23? to form a valve end to cooperate with the seat surrounding the opening in the bushing. The spring 236 is held in place by the drilled bushing 250 asin the previous embodiment.

The by-pass valve is somewhat simplified and is of the hollow or tubular type comprising a thimble 2-12 closed at its left hand end and held biased to the left against the sleeve 2&0 by the spring 243 quite like that in the'previous embodiment. The cylindrical sleeve of the thimble 2E2 normally spans and closes the angular extension 244 of high pressure chamber 243, but when the valve is moved to the right in the manner explained previously, the radial ports 2&5 therein register with this passage 24% and permit high pressure fluid to flow into the valve and out through its open right hand end into the low pressure chamber in cap 2E2.

The operation of the embodiment just described is identical with that of the first embodiment and need not be repeated. The improvements in this embodiment consist in the simplification of the whole structure and in the provision of space for a larger number of accumulator plungers. Obviously if itis desired toreduce the capacity and increase the working pressure these plungers may have reduced ends working through sleeved bushings as in the first a ler ens *3) bodiment. an desired reduction in the accumulater capacity can be efiected by removing the spring from one or more of the plungers, leaving the plungers in the cylinders to close off communication between the high and low pressure cap chambers. It is obvious that if desired a manual pump can be embodied in this arrangement in a manner similar to that described in At this point it might be desirable to enumerate the advantages accruing from the use or accumulators constructed in accordance with the present invention, They are as follows:

A. They permit simplification of the control valves which can be formed without a through bypass in the neutral position. The use of a builtin relief valve in the control valves or the use of a separate one somewhere in the system is also eliminated.

B. Multiple sets of control valves and motors may be operated from a single high pressure main supplied by one accumulator and pump.

(3'. Since the high pressure head is always maintained in a pipe corresponding to the high pressure pipe ill of Fig. 1 any one or all of the control valves in a multiple valve installation may be operated without affecting the rest.

D. The life of the power pump used in installations of this type is materially increased due to the by-passing of the fluid at or near zero pressure instead of at the relief valve pressures pf earlier systems.

E. The system operates cooler due to zero pressure by-passing.

F. The auxiliary pump permits emergency operation.

I claim:

1. In a hydraulic accumulator for use between a liquid pump and a control valve for a hydraulic motor, in combination, a housing having a chamber for connection to the pump, a chamber for connection to a liquid sump and a chamber for connection to the motor control valve, a check valve permitting flow from the first chamber to the third but preventing reverse flow, a spring pressed accumulator plunger ex- .posed at one end to liquid in the third chamber and at the other to liquid in the second chamber, a by-pass valve mounted to close a passage between the first and second chambers and means operable when exposed to pressure in the first chamber greater than that necessary to load the accumulator plunger to open said bypass valve and means controlled by said plunger to hold said by-pass valve open.

2. In a hydraulic accumulator for use between a liquid pump and a, control valve for a hydraulic motor, in combination, a housing having a chamber for connection to the pump, a chamber for connection to a liquid sump and a chamber for connection to the motor control valve, a check valve permitting flow from the first chamber to the third but preventing reverse fiow, a spring pressed accumulator plunger exposed to liquid in the third chamber, a bypass valve positioned to close a passage between the first and second chambers, means operable when exposed to pressure in the first chamber greater than that necessary to load the accumulator by moving said plunger to compress its spring t open said by-pass valve, and means to maintain said by-pass valve open until the accumulator plunger has at least partially returned toward unloaded position.

3. In a hydraulic accumulator for use between to a liquid pump and a control valve for a hydraulic motor, in combination, a housing having a chamber for connection to the pump, a chain ber for connection to a liquid sump and a chamber for connection to the motor control valve, a check valve permitting flow from the first chamber to the third but preventing reverse flow, a spring pressed accumulator plunger exposed to liquid in the third chamber, a bypass valve arranged to close a passage between the first and second chambera means operable when exposed to pressure in the first chamber greater than that required to load the accumulator plunger to open said by-pass valve, and means in cluding said loaded plunger to confine a liquid column to maintain said by-pass valve open.

4. In a hydraulic accumulator for use between a liquid pump and a control valve for a hydraulic motor, in combination, a housing having a chamber" for connection to the pump, a chamber for connection to a liquid sump and a chamber for connection to the motor control valve, a check valve permitting flow from the first chamber to the third but preventing reverse how, a spring pressed accumulator plunger exposed to liquid in the third chamber, a by-pass valve mounted to close a passage between the first and second chambers, means operable when exposed to pressure in the first chamber greater than that necessary to load the accumulator to open said by-pass valve, means to confine a liquid column to maintain saidby-pass valve open and a pas sage adapted to drain said column to the second chamber, said passage being closed by said accumulator plunger when loaded and opened when the plunger is unloaded.

5. In a hydraulic accumulator for use between a liquid pump and a control valve for a hydraulic motor, in combination; a housing having a chamber for connection to the pump, a chamber for connection to a, liquid sump and a chamber for connection to the motor control valve, a check valve permitting flow from the first chamher to the third but preventing reverse flow, a spring pressed accumulator plunger exposed to liquid in the third chamber, a by-pass valve mounted to close a. passage between the first and second chambers, mean operable whenexposed to pressure in the first chamber greater than that necessary to load the accumulator to open said by-pass valve, means to confine a liquid column to maintain said by-pass valve open, a passage adapted to drain said column to the second chamber, said passage being closed by said accumulator plunger when loaded and opened when the plunger is unloaded, and a light spring adapted to close said by-pass valve when said column is drained 6. A hydraulic accumulator for use with a sumpreservoir and between a mechanically operated liquid pump and a control valve for a hydraulic motor, comprising, in combination, a housing forming three separate chambers, the first for connection to the high pressure side of the pump, the second for connection to the sump and the third for connection to the motor control valve, a check valve controlled passage for supplying the third from the first chamber, a spring pressed accumulator plunger having the end to be liquid loaded exposed to the third chamber and its spring end to the second chamber, a duct intersecting the bore in which said plunger operates and being uncovered by the plunger for communication with the second chamber only when the accumulator is unloaded,

aaonsas ll a relief valve arranged to connect the first chamber to said duct when pump pressure becomes excessive, a passage between the first and second chambers, a balanced by-pass valve. plunger lightly biased to close said last mentioned passage, one end of said valve plunger being exposed to said duct, whereby, when'said relief valve opens, pressure on said valve plunger will overcome the bias and relieve the liquid pressure to the sump.

7. A hydraulic accumulator for use with a sump reservoir and between a mechanically operated liquid pump and a control valve for a hydraulic motor, comprising, in combination, a housing forming three separate chambers, the first for connection to the high pressure side of the pump, the second for connection to the sump and the third for connection to the motor control valve, a check valve controlled passage for supplying the third from the first chamber, a spring pressed accumulator plunger having the end to be liquid loaded exposed to the third chamber and its spring end to the second chamber, a duct intersecting the bore in which said plunger operates and being uncovered by the plunger for communication with the second chamber only when the accumulator is unloaded, a relief valve arranged to connect the first chamber to said duct when pump pressure becomes excessive, a passage between the first and second chambers, a balanced by-pass valve plunger light ly biased to close said last mentioned passage, one end of said valve plunger being exposed to said duct, whereby, when said relief valve opens, pressure on said valve plunger will overcome the bias and relieve the liquid pressure to the sump, said relief valve being biased to close upon slight reduction in pressure in the first chamber whereby liquid is trapped in the duct to hold the by-pass valve open until the accumulator is unloaded to relieve the duct to the third chamber.

8. An accumulator as defined in claim 6 in which a plurality of accumulator plungers are provided between the second and third chamber, only one of which is in control of the said duct, all of said plungers being movable in uni son when being loaded or unloaded.

9. An accumulator as defined in claim 6 in which a manually operable plunger pump is provided in a bore connecting the second and third chambers, to transfer oil from the sump to load the accumulator plunger, said pump providing a pressure to close the check valve and render the other valves inoperative in the absence of fluid pressure from the mechanical pump.

10. In a hydraulic accumulator of the type described, in combination, a housing comprising a central section and end plates constructed and assembled to provide a chamber at each end of the central section, a plurality of bores extending parallel to each other and from chamber to' chamber, a spring Dressed accumulator plunger in at least one of said bores and including valving means, a check valve, a relief valve and a by-pass valve, all of said valves being aligned in another of said bores, and being adapted to open in the sequence named, said plunger valving means being in control of the closing of the bypass valve.

11. In a hydraulic accumulator of the type de- I scribed, in combination, a, housingcomprising a central section and end plates constructedand assembled to provide a chamber at each end of the central section, a plurality of bores extending parallel to each other and from chamber to chamber, a spring pressed accumulator plunger in at least two of said bores, a check valve, a relief valve and a by-pass valve, all of said valves being aligned in another of said bores, and passages and ports associating one of said plunger bores with the valve bore between the relief and by-pass valves whereby the position of the plunger in that bore controls the operation of at least one of said valves, said relief valve, when open, being arranged to deliver fluid to operate the bypass valve. I

12. In a hydraulic accumulator of the type described, in combination, a housing comprising a central section and end plates constructed and assembled to provide a high pressure chamber at one end of the central section and a low pressure chamber at the other, a plurality of bores extending parallel to each other and from chamberto chamber, a spring pressed accumulator plungerin at least two of said bores, -a check valve, a relief valve and a by-pass valve, all of said valves being aligned in another of said bores,

passages and ports associating one of said plunger bores with the valve bore whereby the position of the plunger in that bore controls the operation of at least one of said valves, and a manually operable pump having a plunger reciprocable through the end plate and forming the low pressure chamber and in one of said bores to transfer liquid from the low pressure to the high pressure chamber.

13. In a hydraulic accumulator of the type described, in combination, a housing comprising a central section and end plates so constructed and assembled as to provide a high pressure chamber at one end of the central section and a low pressure chamber at the other, a plurality of bores extending parallel to each other and from chamber to chamber, a spring pressed plunger in at least one of said bores and movable under the action of fluid in the high pressure chamber, an inlet passage in said central section intersecting another of said bores at two spaced positions, a separate valve in said last mentioned bore between each of said positions and the adjacent chamber, a third valve in the same bore with the other two but intermediate the said positions and in communication with but one of them, a spring normally closing the third valve, said spring-pressed plunger being arranged to be in control of the discharge of the third valve.

14. In a hydraulic accumulator of the type described, in combination, a housing comprising a central section and end plates so constructed and assembled as to provide a chamber at each of opposite ends of the central section, a plurality of bores extending parallel to each other and from chamber to chamber, a spring pressed plunger in at least one of said bores, an inlet passage in said central section intersecting another of said bores at two spaced positions, a separate valv in said last mentioned bore between each of said positions and the adjacent chamber, a third valve in the same bore with the other two but intermediate the said positions and in communication with but one of them, a passage connecting the opposite end of said third valve with one of the plunger containing bores so as to be uncovered by the plunger when positioned by its spring and closed by the plunger when the spring is loaded.

15. In a hydraulic accumulator of the type described, in combination, a housing comprising a central section and end plates so constructed and assembled as to provide a chamber at each end 13 of the central section, a plurality of bores extending parallel to each other and from chamber to chamber, a spring pressed plunger in at least one of said bores and adapted to assume an unloaded position under the action of its spring from which position it is movable under fluid pressure on one end thereof, an inlet passage in said central section intersecting another of said bores at two spaced positions, a pair of valves in said last mentioned bore, one between each of said positions and the adjacent chamber, a third valve in the same bore with the other two but intermediatethe said positions and in communication with but one of them, a passage connecting the opposite end of said third valve with one of the plunger containing bores, the

plunger in said bore being constructed and positioned to close said last mentioned passage in all except the unloaded position of the plunger.

16. In a hydraulic accumulator of the type described, in combination, a, housing comprising a central section and end plates so constructed and assembled as to provide a chamber at each end of the central section, a plurality of bores extending parallel to each other and from chamber to chamber, an inlet passage in said central section intersecting one of said bores at two spaced positions, a, check valve in said last men-, tioned bore opening from one of said positions into the first of said chambers, a pressure balanced valve slidable in the same bore to connect or shut of! the other intersection from the second chamber, a spring urging said balanced valve toward closed position, a compartment to receive fluid pressure to open said balanced valve against said spring, a relief valve adapted when open to connect said inlet passage 'to said compartment, a passage to drain said compartment to the second chamber, said last mentioned passage intersecting one oi the other bores, an accumulator plunger in each of the other bores, and

valve means associated with the plunger in said one of the other bores.

1'7, In a hydraulic accumulator of the type described, in combination, a housing comprising a central section and end plates so constructed and assembled as to provide a chamber at each end of the central section, a plurality of bores ex-. tending parallel to each other and from chamber to chamber, an inlet passage in said central section intersecting one of said bores at two spaced positions, a check valve in said last men-- tioned bore opening from one of said positions into the first of said chambers, a pressure baianced valve slidable in the same bore to connect or shut off the other intersection from the second chamber, a spring urging said balanced valve toward closed position, a compartment to receive fluid pressure to open said balanced valve against said spring, a relief valve adapted when open to connect said inlet passage, to said compartment, a passage to drain said compartment to the second chamber, a spring pressed accumulator plunger in one of said bores and exposed to the first of said chambers, said drain passage entering said plunger bore and said plun er being constructed to close off the drain passage only when loaded by liquid pressure in the first chamber.

18. In a hydraulic accumulator of the type described, in combination, a housing comprising a central section and end plates so constructed and assembled as to provide a chamber at each end of the central section, a plurality of bores extending through the central section from chamber to chamber, an inlet passage in said central section intersecting one of said bores at two spaced positions, a separate valve in said bore between each of said positions and the adjacent chamber, one of said chambers being open for discharge at low pressure, the remaining bores being closed against communication between chambers and at least one bore housing an accumulator plunger spring pressed toward .the other chamber, and means controlled by the position of said plunger to re ulate the closing of ,the valve opening into'the discharge chamber.

19. The hydraulic accumulator as described in claim 18, in which each chamber houses a spring,

- said springs respectively maintaining said valves closed.

" WILLIAM T. S'IEPHENS.

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