US2592613A

US2592613A - Self-compensating accumulator

Info

Publication number: US2592613A
Application number: US753176A
Authority: US
Inventors: Robert E Snyder
Original assignee: SNYDER OIL TOOL CORP
Current assignee: SNYDER OIL TOOL Corp
Priority date: 1947-06-07
Filing date: 1947-06-07
Publication date: 1952-04-15
Anticipated expiration: 1969-04-15

Description

April 15, 1952 R. E. SNYIDER SELF-COMPENSATING AccUMuLAToa Fild June 7, 1947 3 Sheets-Sheet 1 April 15, 1952 R.: sNYDER SELF-COMPENSATING ACGUMULA'IOR Filed June "7, .1947'` 3 Sham Sheet 5 .fm/enter A ztor'nejg.

Patented pr. l5, ,1952

UNITED STATES PATENT OFFICE 2,592,613 sELaCoMeENsA'rING ACCUMULATOR Robert E. Snyder, Pasadena, Calif., assignor to `Snyder Oill Tool Corporation, Los Angelesy Calif., a` corporation of California sppueauoame 7, 1947, serial No. 753,176

22 Claims, 1

My invention relates generally to hydro-pneu matic accumulators for reducing and cushioning the shock eiects produced by surges of liquid and pressure vibrations in hydraulic systems. More particularly, my invention relates to n'ieans used in connection with such accumulatore to automatically adjust the same for optimumV op eration over a wide range of averagey working pressures in a hydraulic system.

Hydroepneumatic accumulators are often con; structed inr the formed of a` closed container illed with gas under a predetermined pressure', said` container being placed in communication with the hydraulic system to be protected Wl-'ereby sudden changes in' the hydraulic pressure' are cushioned' by compression. of tllie` gas in tlie-` gjs chamber of the accumulator. Furthermore, itis common practice to place zrlo'vable sepaator'y means between the liquid of the lfiy'd'r'au'licV systern and: theV gas contained? in the' accumulator invv havebcen used" ini accumulatorsi previous con'- struction' for example', in my depending appli; cationfor United States'i Letters Patenti Serial'- No. 7l0fl90yled November`18,l1i946 arid entitled Accumulatoi-PI' disclose andi claim novell sepa ratory means-for the purpose above deseribed- For the"V purposes off thlis disclosu'eg tlfie follows: ing' terms: andi designations will be used".V

The average' Hydraulic line` pressure willi be designated as P, witlvarious' different aver-alge pressures being designated as1Pi,-P2, i etcz The initial. pressure oi the' gas :irlA tlie aocuinu" later before commencingl the operatiori of thehyd'raulic system will be termed the precharge` pressure" and will be designated as Ppi-.i-

VChanges in line pressure above*andL belowftlie average linepressure-PWill be designated spL In" normally operating"hydrauliosystems this V" iatior'i4 p in the ave'ia type pressure recorders: culat'on', the pressurewv variation p' is usually noted in itsrelation to P" as a certain percentage' thereof.

Pressure variationsp are usually occasioned in the-line by fluctuating movementof" tnehydraulic fluid or by sl'ioclr'waves` set-up' therein from the pump, valves, or' the"operating` equip# nient; The output from' aL reciprooatie pump 1 rate'. This variation in uuidout'put-iito; the' desea' per au@ ia estese f the average einer pistons, bagsiand combinations of thesey ele entsy gel li'ne pressuielf" may runl to aV thousand (or merel pounds per sjui'iei-ich` and can be readilyf recorded onf variou'ss'tandafti For purposes of' cal-Y i eine at apouticoa.- P;

oneuniiorm, becausetlie velocity of the pi'stiij is cyclically non-uniform in both poWer and steam piston pumps such as are commonly used. Thus `Wl'ii'le a given pump has an average dis# charge rate per cycle, the piston movement actually causes a variation in the discharge over lie` time for' a given cycle during Wlfiiclrit; te from some value below to a" value` altve;

results periodic pressurel variations 13"' as tHe uid is alternately rammed into or starved fwron` the line ata rate respectively: g'reate'or l'es'fs` th the average How 'ratei The arrOllzlt ofillld a predetermined range.

necessarily? bey as lowf asf possible; the 'precio/tele" sldw,4 ap tilizedtofllyfabonne it.- Th' volume S from a double-actin which will produce harmful effects in the system. 'I'he optimum value of p will, of course, be different for various hydraulic systems, but it can be determined for any particular system either by experiment or by calculation.

Given the allowable value of p and a constant value of S for any given hydraulic system, the volume V of the gas chamber is lxed. For example, let the desired p equal 5% of P1. The fixed value of V is then determined by Boyles law as follows:

This S:V relationship is true regardless of the average working pressure in the hydraulic system, providing of course, that said working pressure is initially balanced by a suitable precharge pressure in the gas chamber of the accumulator.

Since the surge volume S is usually dependent upon the physical dimensions of a pump or similar element in the hydraulic system, and since liquids can be consideredras incompressible, the value of S can, as previously stated, be considered as a constant for a given pump over a considerable range of average working pressures P.

If an accumulator is to adequately protect a hydraulic system which may be operated over a wide range of working pressures, it is necessary to change the precharge pressure every time the working pressure is changed in order to maintain the S :V ratio within allowable working limits.. Such a procedure is, in many cases, impractical since in most hydraulic systems such, for example, as mud circulating systems used in connection with rotary well drilling equipment, thev working pressures vary over a wide range, and often unexpectedly. Thus accumulators which are intended for use in connection with a. widely varying average working pressure should incorporate means to automatically adjust and maintain the initial or precharge pressure Ppr in the gas chamber substantially equal to the hydraulic working pressure at all times and in a manner which will assure that the ratio of surge volume to gas volume does notl exceed a predetermined value, thus keeping the pressure variations p' below their allowable upper limit at all times.

The mode of operation just described may be termed broadly automatic adjustment of precharge pressure or self-compensation, and it is -with this phase of accumulator design that the present invention deals.

One object of my invention is to provide a hydro-pneumatic accumulator in which the gas precharge pressure is readily and quickly adjusted to equal that pf the average working pressure in the hydraulic system.

Another object of the invention is to provide means for` automatically adjusting the above described precharge pressure in direct response to variations in the average line pressure.

A further object is to provide pressure compensating means which can be adapted for use with various kinds of conventional accumulators.

Still another object of my invention is to provide self-compensating accumulator means of the class described which is assembled from subassembly units, one of which is designed to provide optimum protection against surge pressures Voccasioned by the particular surge volumes S, in

a given hydraulic system, and another of which is designed to provide suitable precharge pressure adjustment over the desired range of average Working pressures in said system.

A further object is to provide an accumulator of the class described in which the size of parts which may be subject to excessive wear is kept to a minimum with said part being easily replaceable.

The foregoing and other objects and advantages of my invention will become apparent from a consideration of the following description of accumulator structures embodying my invention.

Briefly described, my invention as illustrated herein is embodied in a hydro-pneumatic accumulator comprised of two assemblies, one of which may be a substantially conventional accumulator designed in accordance with the surge volume to be protected againsty and taking into consideration the frequency of said surges. This first unit will be referred to as the surge control section or unit.

The other unit or assembly of the accumulator embodying my invention is connected to the surge control unit by a gas line to the gas chamber thereof and by a hydraulic line to the hydraulic system in which the accumulator is incorporated. The other unit is referred to herein as the precharge pressure control unit or pressure compensator, two embodiments of which are illustrated and described.

In one form, the precharge control unit is comprised of a relatively large volume cylinder having movable separatory means such as Va piston therein. The interior of the cylinder` is thus divided by the separatory means into two compartments; one compartment is communicated through a restricted passage to the hydraulic system, and the other compartment through a similar passage with the gas chamber of the surge control unit. The eiect of this arrangement is that the piston in the precharge control unit moves in the cylinder (relatively slowly because of said restrictions) compressing the gas on one side of said piston until the piston 0ccupies a position wherein the gas pressure and hydraulic pressure operating thereon are equal. Due to the restrictive communication between the precharge control unit and the hydraulic system," the piston in the precharge unit is relatively unaffected by the surge responsive pressure variations p', these being cushioned by the operation of the surge control unit.

The second embodiment of the precharge control unit described herein includes a slide valve operating in response to the pressure in the hydraulic system and controlling the delivery of gas under relatively high pressure to the gas chamber of the accumulator. This second arrangement is such that when the working pressure in the hydraulic system reaches a value greater than the then precharge pressure in the accumulator, the valve is operated to admit gas from a gas bottleA into the gas chamber of the accumulator, thus bringing the precharge pressure up to a valve equal to that of the hydraulic system. If, on the other hand, the working pressure in the hydraulic system drops, the Valve is operated in a different direction to release gas from the chamber in the accumulator, thus to bring the precharge pressure down to the value in the hydraulic system.

v The two units making up my novel accumulator structure can be combined in various ways and several possible arrangements are illustrated and described.

For a more detailed description of the various embodiments of my invention, reference should now be had to the attached drawings ill-which:

Figure 1 is a diagrammatic elevational section of an accumulator system embodying my invention;

`Figure 2` is a partially sectioned elevational view of an actual structure embodying the prin ciples illustrated in Figure 1;

- Figure 3 is a partial elevationalY section illustrating a modified form of a surge control unit such as may be employed in Figure 2;

@Figurel 4 is a plan view partially sectioned illustrating an in line arrangement of the elexnen'ts illustrated schematically in Figure l; and,

Figure 5 is a diagrammatic partially sectioned elevational view illustrating a modified form of an accumulator system embodying my invention. Referring now to Figure 1, a diagrammatic illustration of one form of my invention, it will be seen that I have indicated the surge control unit generally by the number I0, and the precharge pressure control unit bythe number II. The surge control unit I is of generally cylindrical shape, being comprised of an upper cylindrical chamber 2| and a relatively short lower cylinder 20. The walls of the lower cylinder 20 are bored. honed, or otherwise machined to provide a smooth operating surface to receive a movable piston I4. The piston I4 is provided with packing rings I so as to form a relatively fluid-tight separation between the lower chamber and the upper chamber 2|. As indicated in Figures 1 and 2, the piston I4 is free to move vertically somewhat, being limited at the lower end by the bottom of the cylindrical chamber 2|),A and at the upper end of its movement by a stop ring I9 fixed into the Wall of the cylinder 20. However, its total possible stroke is relatively short. l A

Since the piston I4 never enters the `upper chamber 2|, the inner walls' thereof may be left unmachined, thus minimizing the amountv of honing required in the surge unit.

The lower compartment 2D is communicated with the hydraulic system to be protected by means of a conduit 21 connected at opening 25 to 1 the output of the pump or similar element (not shown) in the hydraulic system. In the present instance. the flow of the fiuid through the hy draulic system is in` at the opening 25 and out at the opening 21, passing through a screening device 2B. Thus the surges in the liquid passing through the hydraulic system are directed in ram fashion through the conduit 21 directly to the surge control unit I0.

` The volume I3 of the upper chamber 2| is precalculated so that its relationship with the volume S of the surges in the hydraulic system is such that the pressure variation p will always be less than the predetermined harmful amount.

Mounted within the piston I4 is a exible cupshaped diaphragm I6 which is limited in its movement by an upper perforated plate I8 and a lower perforated web I1 in the piston I4. The volumetric capacity of the cup-shaped diaphragm I6 should be at least equal to and preferably greater than the surges S to be absorbed. Thus when the precharge pressure Ppr in the upper compartment 2| is equal to theaverage Working pressure in the hydraulic system, the surges are cushioned by alternate collapsing and expand-4 isn . systeml at the conduit 21.

ing of the diaphragm I 6, which in turn alter-1 nately compresses the gas in the compartment 2|. Due to the vibratory action of the diaphragm I6 which is caused by the surges in the hydraulic system, the piston I4 will, when the precharge pressure is properly balanced against the hydraulic pressure, assume an intermedia-te position between the stop ring I9 and the lower end of the chamber 20. The piston will come to rest in this intermediate position and substan tially the entire surge motion will be taken up-by motion of the diaphragm Iii.

AIt will be remembered that the cushioning eiieot of the gas in the chamber 2| is fully effective only so long as the precharge pressure Ppr is substantially equal to the average hydraulic pressure and the ratio of S to V does not exceed the allowed maximum. For practical purposes, however, it is often necessary to contemplate av considerable range of average Working pressures. while the volume of the surges from a given pump remains relatively uniform regardless oi the average working pressure. i

To accomplish automatic adjustment of the precharge pressure Ppr I have provided the pres-l sure compensating unit II, which is connected by means of ducts 30 and 3| to the gas chamber 2| of the surge control'unit and by ducts 28 and 219 to the hydraulic system, the latter connection being made at the conduit 21. In the embodis ment illustrated diagrammatically in Figure I, the pressure compensator II is comprised of a cylinder IIa having smooth inner walls 4Q and' having a movable piston 4I positioned therein. The piston 4| is provided with packing rings 42 whereby the piston separates the pressure adjusting unit II into two

compartments

43 and 44. The uppermost 43 of these compartments is a gas chamber and is in communication as previously described with the gas chamber 2| of the surge control unit I0. The lower compartment of the precharge pressure adjusting unit II is a hydraulic iiuid chamber and is, as previously described, connected to the hydraulic Thus it will be seen that the piston 4| provides a movable separatory means between the gas chamber 43'and the uid chamber 44 of the precharge pressure adjusting unit II.

The desired restrictions in communication be tween the unit I and the hydraulic line and surge control gas chamber are conveniently provided by

restrictive orifices

32 and 33 connected in the liquid and gas ducts 28--29 and 35i-3|, respecV tively. In the present instance these orifices are adjustable, although the invention is not; limited to the adjustable feature.l A

It will now be noted that due to its ability to move up and down the inside of the cylinder 40, the piston 4I will tend to assume av position wherein the gas pressure in the upper compartment 43 is equal to thevfluid pressure in the lower compartment 44. By reason of the restricted flow in conduits 28-29, only relatively slow changes in hydraulic pressure are communicated to the chamber 44. Thus the pressure in the chamber 44 is actually an average between the low and high values of the fluid pressure in the hydraulic system which are occasioned by the pressure variations p. Thus since the pressures in the gas compartment 43 and the uid compartment 44 are equal, the gas pressure inthe compartment 43 is the desired pressure Per. This pressure Pm` is communicated as4 mentioned, tliroiighl the duct Sil-31| to the gas chamber of 7 thesurge control unit I0. By reason of the addition of the restrictive orifice 33 in the duct 30- 3|, the relatively high frequency pressure variations in the gas chamber 2| of the surge control unit I are not communicated back to the gas chamber 43 of the pressure control unit II. The

piston 4I once it has assumed its position of balance, need not necessarily move until the average working pressure in the hydraulic system changes, and for this reason the walls 40 of the cylinder I Ia are not subjected to .a large amount of wear or scrubbing action as they would be if the piston 4| moved continually in response to the pressure variation p.

Turning now to a discussion of an actual structure embodying the principles illustrated in Figure 1, reference should be had to Figure 2. It will be noted in Figure 2 that the operative section of the surge control unit i0, wherein the piston I4 is located, is fabricated as a separate portion of the unit. Said operative portion is comprised of a cylindrical portion 2! formed with attachment flanges l0 and 'll on the lower and upper ends thereof and preferably is only of sui`1- cient length to provide adequate available volume to contain the fluid surge of the system for which it is designed, depending of course, on the type ofV separatory means used in the unit. In the construction of unit I0, shown in Figure 2, the piston |4 slides on the smooth inner face of the cylindrical portion 20. .An obvious alternate structure (not shown) would be torprovide a renewable liner within cylinder 20 in which piston I4 might slide and which could be renewed when it became worn beyond a useful limit. The upper section 2| of the control unit I0 is similarly fabricated in the form of a cylinder having flanges I2 and 13. Thus it will be seen that the surge control unit is made up of separate sub-sections which may easily be assembled in various combinations to suit various operating conditions.

The entire surge control unit I0 and the pressure control unit II are mounted on a base casting 60 which is provided with a base flange 8| and with flange receiving faces 62, S, 54, and S5, each of which is adapted to receive an attachment flange of conventional design which may be secured thereto by means of bolts 63.

Passages 25 and 2l are formed within the base.

casting 60 and a screen device 26 is interposed to screen the hydraulic fluid as it passes through the casting. The accumulator embodying my invention may be interposed in a hydraulic system as indicated in Figure 2 by attachment in a pipeline wherein a flanged pipe 66 constitutes the upstream section and asimilar anged pipe 6l constitutes the downstream section. Sections 86 and 61 are secured to the attachment faces 62 and 63 respectively by means of flange bolts 6E as previously mentioned.

The surge control unit I0 is secured to the upper flange receiving portion 64 and communicated with the hydraulic system through passage 21 formed in the base casting 60. The pressure control unit is similarly attached at the flange receiving portion 65.

The surge control unit I0 and the pressure control unit II are provided with upper closures I and 82 respectively, which are attached by means of flange bolts 68 to upper flanges 'I3 and 8 I, respectively, of the two units.

Located at the bottom of the pressure control unit II is a clean-out valve 9| which is mounted in a removable valve seat 90 and is held normally closed by a compression spring 93 acting throughr s valve stem 92ans anabutment 94 to hold the valve 9| closed against the seat 90. The purpose of the blow-out valve 9| is to allow the contents of the fluid chamber 44 in the pressure adjustment unit I I to be discharged through a passageway 95 directly into the hydraulic system whenever the latter is shut down and the pressure therein drops below that of the precharge pressure. This prevents an accumulation of mud and sand from settling and remaining in the liquid chamber 44 should such foreign matter be present in the hydraulic uid.

Itis contemplated that the minimum operating pressure in any hydraulic systeml requiring the protection of an accumulator, will be somewhat above atmospheric. For this reason it is necessary that Ythe precharge pressure in the gas chamber of the surge control unit I0 be considerably above atmospheric before operation of the hydraulic system is even started. For the purpose of providing this minimum precharge gas pressure, a gas bottle 46 (shown in Figure 1) containing a gas, preferably but not necessarily nitrogen, under high pressure` is communicated through a conduit 45 to the gas chamber 43 of` the pressure control unit II. A valve 49 controls the ow of gas from the bottle 46 into the chamber 43. Should it be desired to disassemble the unit or possibly to lower the lower limit of the operative pressure range, gas may be discharged from the system through a `valve 50. Gauges 47 and 48 are provided to indicate the gas pressure in the gas bottle 46 and the pressure control unit I| respectively. l

Figure 3 illustrates an alternative form of surge control element which may in some cases be used in lieu of the element comprising the piston I4 and the diaphragm I6. VThe piston |30 illustrated in Figure 3 is similar in form to the piston 4I and is provided with packing rings I5 whereby to form a hermetic seal withthe walls of the cylinder 20. The piston |30 is supported in an approximately centered intermediate posi-` tion in the cylinder 20 by means of a pair of springs ISI and |32 respectively which thrust in opposite directions on the upper and lower ends of the piston.V The operation of the piston |30 in response to surges in the hydraulic system consists in a vertically reciprocating motion withinthe cylinder 25. The forces of the springs I3I and |32 are preferably just suicient to overcome the frictional resistance of the piston |30 and its packing rings I5 against the walls of the cylinder 20. Thus substantially all the resistance to surge responsive motion is produced by the compression of the gas in the chamber above the piston |30 and the piston will more readily cooperate with the compensator to insure optimum results.v

In Figure 4 an alternative arrangement of the elementsV of Figure 1 is illustrated wherein the gas chamber of the surge control unit I0 and that of the pressure compensator are directly connected without any restriction between them. The entire unit is disposed horizontally and is connected in the hydraulic system in such a manner that the surge absorbing element is directly acted upon by the hydraulic fluid, and the pressure compensating piston is responsive to pressure variations at a downstream point in the line. The line is, in eiect, by-passed around the accumulator by the pipe IOI. If the pipe |0I is of sufficient length and the elements are arranged substantially as shown, little if any restriction may be needed between the downstream side of the line and the pressure compensator. However, for maximum sexi-puny or installation I` prefer to provide oriiice plates |93 of various sizes which can be clamped in place between liange llllv on the conduit |02 and the ange portion 8| of the compensator, the size of the orifice depending upon the characteristics of the system.

As `in the form shown in Figure 2, the pressure control unit comprises a cylinder Ila having a smooth bore 40 with a piston 4| slidable therein. The Iiange 8e of the compensator is bolted to the iiange 1| of the surge control unit I0 with the latter being directly connected into the line by bolting its other flange to a flange |05 in a tting |05 in the upstream line. In this form of my invention, as shown, the cylinder 2| is omitted but it will be understood that it can be inserted between cylinders 2Q and Ila if desired, depending upon the line vpressure and surge Volume to be encountered.

In Figure 4 I have shown a conventional bag type separatory element in the surge control unit instead of the piston type element of Figures l and 2. A bag |91 of rubber, neoprene or similar suitable elastic material is sealed at its open end to a base plate |88 having a passage |09 therethrough connecting the bag to the gas chamber 43 of the compensator. The base plate |08 may be conveniently clamped between flanges 1| and Eil as shown. A perforated plate IIB, preferably crown in shape, spans the inner end of the passage 21 providing a seat or guard to prevent the bag |81 from blowing out through said passage when the gas pressure inside the bag is considerably greater than the liquid pressure on its outside. A similar perforated plate 99 pro- *icts the bag from blowing out through passage The operation of this form of vmy invention is substantially the same as the rst form, with lthe bag |61 compressing to absorb sudden surges in the line and the piston 4| varying its position in response to variations in average line pressure to thereby maintain the pressure in the gas chamber and bag at all times equal to the average line pressure.

' In Figure 5 a modication of the previously described accumulator is illustrated. In the form of Figure 5 the surge control unit |D is identical in form and operation to that previously described and shown in Figure 3; however, the pressure control unit I I of Figures 1 and 2 is replaced by a modified form indicated by the numerall Ill. This modified pressure control unit comprises a valve structure I which includes a member ||2 slidably supported in a cylinder ||3. The slidable member l2 is operated through compression springs IM, which in turn abut against flexible diaphragme IIS and IIE, respectively. The diaphragms Ii and IIS are supported vin the lower and upper ends respectively ofthe cylinder ||3 by end bells l1 and ||8 respectively. Hydraulic pressure from the conduit 21 is communicated by a duct |29 to the outer face of the lower diaphragm l I5, and gas pressure from the gas cham ber 2| is communicated through ducts |2| to the outer face of the upper diaphragm IIS. Thus when the pressures in the gas chamber 2| and in the hydraulic system are equal, the slidable member is held by the springs ||4 in a central position as illustrated in Figure 5. It will be noted that the interior of the cylinder ||3 is in continual communication through slot |24 in the sliding member I I2, through duct |23 and @hence through duct |2`| with the chamber 2 yWhen the gas pressure in the chamber 2| exceeds the hydraulic pressure in the system, the movable daphragms ||5 and |6 and the operation of the compression springs ||4 is such as to move the slidable member I2 downwardly, placing a port |26 in the slidable member in align ment with a duct |21 which communicates' through a pressure regulator |28 to atmosphere as shown. Thus when the pressure in the gas chamber 2| Vexceeds the hydraulic pressure, the operation of the valve structure will bleed gas from the chamber .2| until the pressure in said chamber is reduced to that of the hydraulic sys tem.

On the other hand, when the pressure in the hydraulic system rises above that in 'the galschamber 2|, the operation of the diaphragm l5 and the compression springs ||4 is such 'as `to move the slidable member |12 upwardly, placing a port |29 in alignment with the conduit |22. thus to conduct gas from the bottle 46 'through the slidable member l2 into the cylinder I |3 and out of said cylinder through ducts `|23 and 12| into the gas chamber 2| in the surge control unit I0. Thus any variations in hydraulic pressure automatically operate the valve structure to produce an equal pressure in the gas chamber 2|. The pressure regulator |28 is provided in the system in order that the minimum Vgas pressure in the chamber 2| will never fall belowv a predetermined amount to which the regulator |28 is adjusted. In this way the lower limit of Ydesired operating pressure range for the hydraulic system may be set by an adjustment of the pressure regulator |28, the upper limit being the pressure of the gas in the bottle B6. u Thus it will be seen that the accumulator structure embodying my invention has the particular advantage, among others, of being universally ladaptable to a wide variety of 'working conditions. It is to be noted in this regard that mud pumps, for example, such as are used in rotary well drilling equipment, are manufactured in a relatively few standard sizes, each of which has a certain cylinder stroke displacement. Consequently, the surge volume S for any given mud pump is known and the surge control unit |;|l may be designed in certain sizes, each of which is suitable for use in connection with a particular type and size of mud pump.

The physical dimensions of the pressure compensating unit are not, however, predetermined by the size of the pump only, but must be calculated to accommodate the particular accumulator to the particular range of working pressures that will be encountered. Thus by manufacturing the pressure compensating unit and the surge control unit in a few standard sizes, accumulators can be assembled to suit any combination yof pump size and press-ure range by selecting the proper units and combining them. This represents a great saving over the methods previously used wherein it was frequently necessary to design and fabricate a complete accumulator for every hydraulic system in which a new ycombination of factors was encountered.

`of the cylinder, place it in a new cylinder and replace the new cylinder (or a liner therefor) in the unit I0.

Since the motion of the piston il in the cylinvder 40 takes place only upon a change of the average` working. pressure of the hydraulic system, such motion is relatively slow and infrequent and the wear on the cylinder 40 relatively small.l Thus the replacement of the cylinder 4t,

while readily achieved, is seldom necessary.

Y Additionally, it will be apparent that while my system of automatic pressure ycompensation is yparticularly well adapted for accumulatore of the type shown in my said copending application, it likewise can be applied to all types of 'accumulators wherein it is desired to change the precharge pressure of the gas in response to the `line pressure of the gas in response to line pressure variations. In these latter cases the particular type and design of the compensating element may, of course, be modified to suit the type of surge units being used. l While the Various accumulator structures shown and described herein are fully capable of achieving the objects and providing the advantages hereinbefore stated, they are illustrative -only of the broad principles of my invention and may be modified by persons skilled in the art without departing from the spirit of the invention. For this reason I do not mean to be limited tothe forms shown and described herein, but

lrather to the scope of the appended claims.

I claim:

1..'In a hydro-pneumatic accumulator for cushioningsurge pressures in a hydraulic system: a surge control unit having a gas chamber,

'aliquid chamber in communication with said hydraulic system, and movable separatory means between said gas and liquid chambers;

`and means responsive to pressure in said hydraulic system to adjust the gas pressure in saldi-'gas chamber, said pressure adjustment means including movable separatory Vmeans urgedin one direction by said hydraulic pres- 'sure and in the other direction by pressure of gas' in said gas chamber and adapted to selectively compress and decompress gas in said chamber to adjust the pressure therein. Y

'2.'A device for adjusting the reactive pressure in a hydro-pneumatic accumulator includ- `ing: a source of gas under relatively high pressure valved passage means connected between Ia gas chamber in said accumulator and said source, vsaid valved means having therein a member movable in one direction to discharge gas from said gas chamber and in the other direction to admit gas from said source into said gas chamber; means to reactively communicate the pressure in said gas chamber to a hydraulic system; and movable separatory means exposed on one side to pressure of said gas chamber and on the other side to pressure in said hydraulic system, said separatory means being operatively `pressure between the gas in said chamber and toryV means in said vessel movable in, said cylindrical portion in response to exterior hydraulic pressure independently of said rst separatory means; said second separatory means having'iiuid tight 'contact with interior walls of said cylindrical portion whereby said rst and second separatory means and said vessel form an enclosed gas chamber of variable volume depending on the position of said second separatory means; means adapted to communicate a hydraulic system to said vessel ends whereby to apply'hydraulic pressure in said system directly to each of said separatory means; and means associated with said communicating means adapted to damp out sudden hydraulic pressure variations in the pressure applied to said second separatory means whereby said irst separatory means will cushion said pressure variations in said system by compressing gas in said gas chamber, and said second` separatory means will compress gas in said chamber to maintain the average pressure thereof substantially equal to the average working pressure in said hydraulic system.

4.. In a hydro-pneumatic accumulator for absorbing surges in a hydraulic system, the combination of means forming a gas chamber havingi a movable wall, and adapted to be connected in a hydraulic line to place said wall in contact with the uid in said line whereby said wall will move in response to dierentials in pressure between the gas in said chamber and the; fluid in said line to balance the same; and means with a movable member forming two compartments of variable volume, one com partment being uid connected to said gas chamberand the other compartment being uid connected to said hydraulic line, whereby movement of said movable member-in response to di'ierentials in pressure between said two compartments will automatically cause a lvariation in the pressure in said gas chamber corresponding to the variations in said line pressure.

5. In a hydro-pneumatic,accumulator for absorbing surges in a hydraulic system, the combination of: means forming a gas chamber having a movable wall, and adaptedv to be connected in a hydraulic line to place said wall in contact with the uid in said line whereby said wall will move in response to differentials in the fluid in said line to balance the same; and

,means for adjusting the pressure in said chamber in accordance with pressure variations in said line which includes a movable piston urged in one direction by the pressure in said gas chamber and urged in the other direction by the fluid pressure in said line, and adapted upon increase in said line pressure to cause the gas in said chamber to be compressed and upon decrease in said line pressure to allow decompression of said gas. Y

6. In a hydro-pneumatic accumulator for absorbing surges in a hydraulic system, the combination of: a cylinder closed at one end and having its other end adapted to be connected in a hydraulic line; a separatory member movably mounted in said cylinder dividing the same into a'liquid chamber in communication with said line and a gas chamber, said memberbeing responsive to sudden pressure variations in said line; a second cylinder closed at both ends; a separatory member movably mounted in said second cylinder to divide the same into a gas chamber and a liquid chamber; passage means 13 communicating said eas chambers; and lmeans providing restricted fluid communication between the liquid chamber of said second cylinder and saidline, whereby said second separa tory member is responsive only V to .average line pressure variations.

7.. In a hydro-pneumatic accumulator for absorblng surges in a hydraulic system, the combination of: a cylinder adapted to have one end connected in ahydraulic line and its other end also .connected insaid line but downstream of said first connection; a separatory member in the upstream end of said cylinder mounted for limited movement therein and responsive to variations in upstream fluid pressure in said line;

a .second separatory member movable in the downstream end of said cylinder` and freely movable throughout a major portion of the length thereof and responsive to downstream pressure variations in ysaid line; means for admitting gas under pressure into .said cylinder between said separatory members; and means `for connecting said cylinder in said line as aforesaid whereby said rst separatory .member will absorb substantially all of the surge in said line in response to sudden variations in line pressure, and said second separatory member will adjust its position in response to variations in the average `line pressure to thereby adjust the gas pressure in said cylinder to said average line pressure.

8. In a hydro-pneumatic accumulator for absorbing surges in a hydraulic system, the combination of: a relatively short surge cylinder open at both ends and adapted to have one of said ends connected in a hydraulic line; a separatory member mounted in `said cylinder for limited movement therein and providing a surge liquid Vchamber in said cylinder; means at .the other end of said surge cylinder of substantial size forming a gas chamber on the other side of said separatory member; and separate means uid connected to said hydraulic line and including yseparatory means independently movable in response to average pressure variations therein to vary the pressure in said gas chamber in accordance with said average line pressure variations.

v9. In a hydro-pneumatic accumulator for cushioning surge pressures in a hydraulic system: a surge control unit having a gas chamber, a liquid chamber in communication with said hydraulic system, and movable separatory means between said gas and liquid chambers; and separate means responsive to pressure in said hydraulic system to adjust the gas pressure in said gas chamber, said pressure adjustment means including independently movable separatory means fluid connected to and urged in one direction by said hydraulic pressure and fluid connected to and urged in the other direction by pressure of gas in said gas chamber whereby to selectively cause the gas in said gas chamber to be compressed and decompressed, one of said fluid connections being such as to restrict the flow of fluid therethrough.

10. In a hydro-pneumatic accumulator for cushioning surge pressures in a hydraulic system: a surge control unit having a gas chamber, a liquid chamber in communication with said hydraulic system, and movable separatory means between said gas and liquid chambers; and separate means responsive to pressure in said hydraulic system to adjust the gas pressure in said gas chamber, said pressure adjustment 14 means lincluding `separatory means movable independently of said :first separatcry means and uid connected to and urged in one direction by .saidhydraulic pressure and iluid connected to and urged in the other direction by pressure of gas in said gas chamber whereby to selectively cause the .gas in said gas chamber to be compressed and decompressed, the fluid connection between said .last mentioned separatory means and said liquid chamber being such as to restrict the flow of liquid therein and thereby cause said separatory member to be primarily responsive to `variations in the average working pressure of said hydraulic system.

11.1n .a hydro-pneumatic accumulator 4for cushioning surge pressures in a hydraulic system: a surge control unit having a .gas chamber., a liquid chamber in `communication `with said hydraulic system, and movable means between said Agas `and liquid chambers; and means independent of said separatory .means responsive to pressure in said hydraulic system to adjust the gas pressure in -said chamber, said pressure adjustment means including a closed cylinder, a piston slidable in said cylinder independently of said separatory means, a lfirst passageway `conruected between one end of said cylinder and said gas chamber, and a second passageway connected between the other end `of said cylinder and said hydraulic system.

12. The construction set forth in claim 1.1 further characterized by having ilow restricting means in said second passageway.

13,. In a hydro-pneumatic accumulator for cushioning surge pressures in a hydraulic system-z a surge control unit having a gas chamber, a liquid chamber in communication with said hydraulic system, and reciprocable separatory means between said gas and liquid chambers, and resilient means to hold said separatory means n a normally centralized position between limits of its motion; and means responsive to pressure in said hydraulic system to adjust the gas pressure in said gas chamber, said pres- A sure adjustment means including independently movable separatory means urged in one direction by said hydraulic pressure and in the other direction by pressure of gas in said gas chamber and adapted to selectively compress and decompress gas in said chamber to adjust the pressure therein. i

14. In a hydro-pneumatic accumulator for, cushioning surge pressures in a hydraulic sys-l tem: a surge control unit having a gas chamber., a liquid chamber in communication with said hydraulic system, and movable separatory means between said gas and liquid chambers; .and means responsive to pressure in said hydraulic system to adjust the gas pressure in `said gas chamber, said pressure adjustment means including independently movable separatory meansurged in a rst direction by said hydraulic pressure and in a second direction by pressure of gas in said gas chamber, a source of compressed gas, and valve means iluid connected to said gas chamber and connected to said separatory means whereby motion of the latter in said first direction admits gas from said source into said gas chamber and motion in said second direction discharges gas from said gas chamber.

l5. In a hydro-pneumatic accumulator for absorbing surges in a hydraulic system, the combination of: means forming a gas chamber having a movable Wall, and adapted to be connected in a hydraulic line to place said wall in contact separatory with the uid in said line whereby said wall will move in response to differentials in pressure between the gas in said chamber and the uid in said line to balance the same; and means for adjusting the pressure in said gas chamber including an independently movable member forming two compartments of variable volume, passage means uid connecting one of said compartments with said gas chamber and passage means providing restricted iluid communication between the other Y compartment and said hydraulic line, whereby movement of said movable member in response to differentials in pressure between said two compartments will automatically cause a variation in the pressure in said gas chamber corresponding to the variations in said line pressure.

` 16. In a hydro-pneumatic accumulator: a base having a passage therein adapted to conduct hydraulic fluid therethrough; an open upright cylinder secured to said base with its lower end in communication with said passage; a separatory member movably mounted in said cylinder having sealing contact with the interior wall thereof and a flexible diaphragm therein to vary the volumetric capacity of said cylinder; limiting means operatively assoicated with said separatory member adapted to resist volume variations in said cylindrical member greater than a predetermined amount; an enclosed vessel secured to the upper end of said cylinder in communication therewith and adapted to receive and contain gas under pressure whereby to resist said volumetric variations; a second upright cylinder secured to said base member and having communication through a restrictive orifice with said passage; a piston in said second cylinder having fluid tight'contact with the wall thereof and movable whereby to divide said second cylinder into chambers of mutually dependent volumes, one of said chambers being a hydraulic fluid chamber with said orifice therein and the other of said chambers being a gas chamber; a closure for the upper end of Vsaid second cylinder; and duct means connected between said gas chamber and said vessel to communicate the gas pressure in said gas chamber with the interior of said vessel whereby to adjust the pressure in said vessel in response to motion of said piston.

17. The construction of claim 16 further characterized by having: a relatively large conduit connected from the lowest point in said hydraulic fluid chamber to said passage; and a spring closed check valve in said conduit positioned and adapted to check flow from said passage through said conduit and permit ilow from said chamber through said conduit.

18. In a hydro-pneumatic accumulator for absorbing surges in a hydraulic system, the combination of: means forming a gas chamber have ing a movable wall and adapted to be connected in a hydraulic line to place said wall in contact with the fluid in said line whereby said wall will move in response to diierentials in pressure between the' gas in said chamber and the uid in said line to balance the same; means including a separatory member movable independently of said movable wall forming two compartments of variable volume, one of which is fluid connected to said gas chamber; and duct means communieating the other of said compartments with said hydraulic system and being resistant to high velocity ilow therethrough whereby to attenuate sudden pressure variations passing to said separatory member and subject said member principally to the average working pressure in. said hydraulic system.

19. In a Yhydro-pneumatic accumulator for cushioning surge pressures in a hydraulic sys-` tem; a surge control unit having a gas chamber. a liquid chamber in communication with said hydraulic system, and movable separatory means between said gas and liquid chambers; and means responsive to pressure in said hydraulic system to adjust the gas lpressure in said gas chamber, said pressure adjustment means including an auxiliary source of gas under substantial pressure, conduit means connecting said gas source to said gas chamber, valve means in said conduit means, and means uid connected to said gas chamber and to said hydraulic system and responsive to differentials of pressure therein Vto operate said valve means in response thereto whereby gas from said source is admitted to said gas chamber when the pressure therein falls a predetermined amount below that in said hydraulic system. Y

20. Apparatus as defined in claim 19 which includes an escape port and said valve means is formed so as to permit exhaust of gas from said gas chamber when the pressure therein exceeds that of said hydraulic system by a predetermined amount.

21. Apparatus as defined in claim 19 in which said separatory member is restricted in its mo'vement and said gas chamber is of substantial size.

22. Apparatus as dened in claim 19 in which the means for operating said Valve means cornprises a member movable in a chamber in response to said diierential pressures to com'- municate said valve means with said gas source in response to said pressure differentials.

ROBERT E. SNYDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Huber Mar. 25, 1947