US2126722A - Variable displacement pump and method of balancing hydrostatic load - Google Patents

Description

Aug' 16', 1938.. E. K. BENEDEK 2,126,722

VARrABLE DISPLACEMENT 'PUMP AND METHOD OF BALANCi NG HYDROSTATIC- LOAD Filed Nov. 2s,- 1954- 5 Sheets-Sheet, 1

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my ma 7 I 3mm //%i% w w a ZELEK KEIENEDEK 95, '97 3/ 5 Sheets-she t s Aug. 16, 1938. E. K. BENEDEK VARIABLE DISPLACEMENTPUMP AND METHOD OF BALANCING HYDROSTATIC LOAD Filed Nov. 26, 1934 .10% ".ELEKKEENEUEKQ NW7 QvJ Patented Aug. 16,

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VARIABLE msrLAcE METHOD OF. LOAD MENT PULIP AND BAIJANCING HYDRO STATIC Elek Be'nedek, Bucyrus, Ohio Application November 26, 1934, Serial No. 754,753

6 Claims.

pumps of the type herein shown when such pumps are designed for very heavy hydraulic loads.

A further object is to provide a new method of maintaining substantially uniform fluid film pressure between the cooperating surfaces of a piston barrel and valve pintle all around the pintle.

Still another object is to provide a new arrange ment for'relatively supporting a valve pintle and piston barrel in connection with a new method of supplying lubricating and/or sealing fluid to between said surfaces.

Still another object is to provide a method and apparatus for maintaining uniform fluid film pressure between thevalving parts of pumps of the class shown and particularly for accomplishing-this during periods when the pump is subjected to very heavy loads as well as during non-pumping operation.

a further object is to provide a methodof lubricating and sealing a valve pintle by which positive pressure lubricant feed is maintained on.

the entire circumference of the pintle and for the entire working length thereof notwithstanding the film diminishing effect of the valve ports whenacting as suction ports.

it. further object is to provide anew piston crosshead construction for radial piston type pumps or motors for minimizing strains and wear on the pistons and their cylinders.

A specific object is to provide a self-aligning piston crosspin mounting and an improved antifrictional journal means for such crosspins in a pump or motor of the class shown.

Another object is to provide a. more eflicient bearing support for the cylinder barrel of a pump or motor of the class shown.

Other objects and features of the invention will become apparent from the following description relating to the accompanying drawings. The essential characteristics are summarized in the claims.

Referring briefly to the drawings:

Fig. 1 is a horizontal central sectional view of a machine (hereinafter referred to as a pump but, in general, useful also as a motor) the view showing certain of the parts including a central valve pintle in elevation; the plane of the section being indicated at i-l on Fig. 2; Fig. 2 is a transverse sectional view'taken substantially along the line 2-2 on Fig. 1;

Fig. 3 is a partially diagrammatic view show-- ing an exemplary form of valve pintle in side ele vation, the view corresponding to the showing of the pintle in Fla. 1;

Figs. 4 and 5 are end elevations of respective ends of the pintle shown in Fig. 3;

Fig. 6 is a. sectional view as indicated on Fig. 3, showing the main lateral inlet and outlet passages and relationship of the cooperating axial bores forming the feed and discharge passages in the pintle;

Figs. 7 and ii are transverse sectional views as indicated by l-'l on Fig. 3, illustrating particularly the hydrostatic forces on the pintle in diiierent cycles of operation of the pump;

Fig. 9 is a fragmentary view of the working portion of the pintle taken at right angles to the showing of Fig. 3 and indicating the hydrostatic forces on the surfaces which are hydraulically fitted with relation to complementary surfaces of the main rotor member of the pump;

Fig. id is a projection of the working end of the pintle and further illustrating the balancing of hydrostatic forces thereon;

Fig. 11 is a diagram showing a development of the tapered working surface of the pintle;

I Fig. 12 is a sectional view of the rotor with the pintle andpistons removed and showing the hydrostatic forces on various surfaces, the. view also showing a modified arrangement of bearings for the barrel;

Fig. 13 is a transverse sectional view of the central portion of the barrel or rotor taken in any transverse plane thereof not intercepting the pistoncylinders and ports;

Fig. 14 is a development of the tapered workin surface of l the barrel, that is the surface coacting with the aforesaid tapered working surface of the pintle;

Fig. 15 is a sectional view taken as indicated on Fig. 12 and showing the hydrostatic pressure forces during operation of the pump;

Fig. 16 is an oil circuit diagram showing the manner in which fluid is delivered by and re-- turned to the pump in a. reversible manner while maintaining positive pressure for lubrication and tively enlarged portion ll maintenance of a hydrostatically balanced oil film and fluid seal at the working surfaces on the pintle and barrel;

' Fig. 1'! is a central sectional view of a suitable double acting check valve for use, e. g., in the oil circuit arrangement of Fig. 16;

Fig. 18 is a fragmentary detail sectional view showing a modified rotor or cylinder barrel and pintle construction for maintaining constant fluid fllm pressure on the coacting pintle androtor surfaces during such times as the pump may be operated at greatly reduced outputpressure or at no load;

Figs. 19 and 20 are views showing a preferred piston crosshead arrangement, Fig. 19 being a partial section on the line l9i9 as indicated on i Figs. 21 and 22 are views corresponding to Figs. 19 and 20 respectively, showing a modification in the piston crosshead construction; and

Figs. 23 and 24 are detail sectional views of the crosspin supporting parts of Figs. 21 and 22.

For the purpose of clearly setting forth the problems involved and solved by the presentv method, a description of the general exemplary arrangement of the pump is here given. The pump structure is,- in general, very close to the arrangement shown and described in my above identified copending application.

Figs. 1 and 2 show the pump casing as comprising two main casing parts i and 2. Preferably these two parts form the entire casing for greater rigidity and reduction of cost and labor in machining, the sections being secured together at the circular shouldered joint 3 as by suitable closely spaced bolts or screws 4. The section i has a very rigid hub portion 5, an end wall 6 and cylindrical flange-like portion 1, the cross sectional shape oi which is shown inFig. 2. The two sections form a substantially cylindrical internal recess 8 between them with cylindrical spaces 9 and 9' at opposite sides, the said spaces being properly machined to receive the supporting bearings for the primary rotor 25 (the barrel) to be hereinafter described. The heavy hub 5 supports a valve pintle M, the pintle having a relapress-fltted, e. g., into a central axial bore of the hub 5 and being prevented from outward movement (to the left, Fig.-

l) with respect to the hub by a shouldered flange I! on the pintle abutting the adjacent end wall surface of the hub.

The working surface of the pintle above re- 1 ferred to is indicated at l 5 and this is preferably very smooth and slightly tapered. The pintle has bearin supporting channels at I and I 6' for receiving cagelm pilot needle roller assemblies I1 and I I, each of the assemblies being such as are more fully described in my copending aplication, Serial No. 651,186, flied November 4, 1932, now Patent No. 2,074,202, dated March 16, 1937. As there explained, the needles of each assembly are spaced apart from each other a capillary distance so that capillary oil fllms form between the individual rollers and thereafter maintain the proper spacing of the rollers with respect to each other. Such assemblies normally mechanically preserve uniform clearance all around the working surfaces while allowing free passage of fluid past the bearings between the individual rollers. The inner afree end face of the pintle Ill terminates shortofthe endsuri'ace 20' of the barrel at 2|. Thellintlelspreferahlyforged from very tough and hard material such as nitrided nitralloy steel. The barrel 25 is of similar hard, tough material and is disposed in telescoping relation to the pintle, the surfaces of the bore 20, adjacent the pintle surface l5, being carefully finished for hydraulic lit with said working surface of the pintle; other portions of the bore affording race surfaces as at Ila and llb for engagement with the needle rollers i1 and H. The surface of the pintle intervening between the spaced bearings I1 and I1 is uninterrupted'except for the ports 80 and M, as shown in Figures 1 and 9.

The mounting for therotor or barrel 25 comprises antifriction bearings 26 and 21, these having inner and outer races 28 and 29 axially abutting accurately formed surfaces on and in the rotor and easing sections i and 2 respectively. Preferably the bearings are of the adjustable type and designed for both radial and axial thrust. The inner race of the bearing 21 is, as shown, secured in place axially by a ring 30 threaded on the right hand end of the rotor and this, due to the various abutment shoulders, maintains both the hearings in position. The rotor preferably has an integral impeller shaft portion at 3| extending through a suitable central opening in the casing member 2.

Since the pressures set up between the rotor and pintle both by reason of the tapered surfaces and the entrapping of the working fluid under high pressure in the space 2| tends to force the rotor in one direction (see small horizontal arrows inFig. 12) and the pintle in the opposite direction (see small horizontal arrows in Fig. 3) it is necessary, in order to preserve'the working clearance adjustment between rotor and pintle, to provide for both radial and axial thrust in the bearings. Preferably the axial thrust capacity of the bearings is about three times the radial capacity, the latter being greatly reducible on account of the balancing of the hydrostatic load around and along the pintle as will be hereinafter more fully explained.

As shown in Fig. 1, the inner race members or rings 28 have comparatively deep grooves or races partially encircling the balls on both sides various operating pressure conditions incident to v reversible, variable delivery pump action, The end thrust of both bearings may be adjusted and any undesired play taken up by the use of shims e. g. (not shown) following conventional practice or shims 3 may be used at the joint .of the casing parts I and 2. In Fig. 12 a tapered roller bearing assembly (210, 28a, and 29a) is shown at the impeller shaft end of the pintle, this type, in some sizes of pumps, being highly efllcient in resisting axial thrust without appreciable rolling friction losses and without being subject to wear due to the increased race surface contact. Here again adjustment is easily effected as previously described. r

The pistons shown at 35, Figs. 1 and 2, operate in radial cylinder bores 36, having reduced port outlets at 36 leading to the bore 20 of the barrel. The pistons have radial extensions in the form 01' enlarged heads 38 guided in accurately fitting radial ways 39 in a. central radial driving flange portion 40 of the rotor which extends outwardly from the main body portion of the rotor in the shown in Figs. 19 to 23 to be later described),

the pins having their opposite ends extending into the embrace of respective reactance tracks in the form of double cam groves 45, formed by the piston reactance assembly which will now be described. The pins may have rollers (not shown) carried on their free ends for-engaging the cam grooves as more fully described in my copending application Serial No. 726,961, filed May 22, 1934.

The piston reactance assembly includes an outer ring 5|) supported as on parallel slide pad surfaces 5 I-, Fig. 2, so that the ring may be shifted from concentric position shown in Fig. 2, to eccentric positions with relation to the- .pintle on either side of the pintle axis, thereby effecting variable delivery and reverse without stopping the rotors- Suitable means for adjustingthe ring may comprise adjustment bars 52; Figs. 1 and 2,

extending through suitable guide bores on opposite sides 'of the casing portion 1. 'The'reactance tracks or grooves 45 or rather the members forming said tracks are antifrlctionally rotatably mounted in the ring'Sfl so as to divide the rolling contact motion necessary to actuate thepistons between the-crosspin mountings and the tracks.

The arrangement comprises, as shown, a pair of antifrictional ball bearing assemblies including i inner and outer race members 60 and BI, each pair of race members supporting between them' a series of balls 52.

The outer race members are securedin-the ring in axial abutment with a 'centralannular rib -63 by means such-as snap rings 54in suitable annular groovesin the ring 50 and the inner races are, thereby also secured a .-in position through the medium of the balls which are embraced .by comparatively deep inner and outer raceway channels as shown. Both inner.

rings as illustrated have their inner surfaces suitably finished to directly provide the outer cam .trackway surfaces of the grooves or tracks 45 for engaging the .pins 42 or rollersthereon (not shown) as desired. The inner cam surfaces of the tracks 45 are provided by separate ring members 55 which may be press-fitted into inner bearingrace members 50 for convenience of assembly, ther'ipgs, particularly the crosspin engaging surfaces,- being, of course, very accurately formed and finished. The track forming rings 65, are, as shown, secured together by a series of coupling bolts or screws 10 (see lower portion of Fig. 1), all the screws having heads 10- suitably engaging one of the rings 55 and threads as at 10" for engaging the other ring.

To determine the piston head space between the rings 50, suitable spacer sleeves 12 are. provided ' bly 50, 50, 55 etc. and in these maximum eccentric on the intermediate portions ofthe screws 10 which spacers overlap both sets of rings 65 and.

Stand definitely space and align allthese parts.

Suitable clearance holes 13 are provided in the radial flange 4|! of the rotor to recei e the bolts and spacers Ill and I2 and these holes are of such size as to accommodate the spacers in the maximum eccentric positions of the reactance assempositions the inner cylindrical surfaces of the holes act to initially drive the rotary parts of the drical bore lot the head.

reactance assembly, thereby removing some of the torque at the start of rotationof the barrel from the piston crosspins as more fully described in my copending application Serial No. 726,961, filed May 22, 1934. I

Referring. now to the modified piston crosshead arrangement of Figs. 19 to 23, it will be seen that instead of mounting the needle rollers 43 direct ly in the transverse bores of the piston heads, suitable separate adjustable mountings Ill) may be provided, such as will allow-transverse self-- (also shown in Fig. 1) for retaining lubricating fluid. Supply ducts (not shown) may also be provided in the piston heads to insure that the rollers will always be lubricated. The rings H2 may be pressed into place in the manner of ex pansion plugs and the inner peripheral surfaces of the rings fit the pins. The'mounting elements I ill have spherical surfaces H3, as shown, closely fitting complementary spherical surfaces in the heads. To assemble such mountings in theheads it is, of course, necessary to make the head in more than one piece. of the head is not illustrated in Figs. 19 and 20. Preferably a ball socket is used as diagrammatically indicated a'tl H by broken lines, the socket 'being screw-threaded into the head and suitably locked inplace.

In Figs. 21 and 22, the spherical mounting members llila support the crosspins and needle rollers 43 as before but are mounted in cylindrical rings H5 shown as split at lliinto two sections. The sections of I I5 in this case have the spherical surfaces complementary to the mounting members lllla for receiving and supporting these members and the-pins, and the assembled sections may be pressed into place in the transverse cylin-,

Fig. 2 4 shows in cross section the spherical member Him and Fig. 23 shows in elevation the inner surface of one of the sections of the ring 5. In operation should the cam grooves 45 be slightly out of registration with each other, the pistons and crosspins 42 would, nevertheless,

Such necessary division operate freely in conjunction therewith because for heavy duty .pumps since all the piston re actance surfaces may be circularly formed by standard machine and grinding methods and the antifrictional support for the rotary parts of the reactance assembly may comprise standard ball or roller bearings further minimizing cost.

Howevenof necessity, this or -any similar con-' struction is, to some extent, hydrostatically unbalanced and the unbalance normally results in almost unbelievable unbalanced mechanical pressures ,on the supporting bearings of the rotor. Further theunbalanced hydrostatic forces tend to or actually do deflect the pintle, and further causeor tend 'to cause the working surfaces to lose lubricant at thesuction port side of the pintle as well as the sealing 'oil film necessary to prevent seizure of thecoacting working surface of the pintle and barrel as well as to seal the valving surfaces against air suction and attendant destructive hammering. Various attempts have been made to balance these forces in this i type of pump without any high degree of success. It has been previously proposed to supply oil film to lubricate the working surfaces through radial passages in the pintle connected with the high pressure delivery line but this spot lubrication is insufllcient to accomplish anything more than to overcome the hydrostatic unbalance for short distances from the discharge ends of the lubricating passages. Larger clearances between the working surfaces of the rotor and pintle overcome the danger of seizure but produce inefiicient pumping both due to excessive slip losses and air bubble suction. Ordinarily, the slip is removed from the space between the free end of the pintle and the closed" end of the barrel bore by radial passages which, among other disadvantages, act as centrifugal pump elements, particularly during high speed, reducing the oil film between the working surfaces .by withdrawing it faster than it can be supplied in the normal operation of the pump. Spring controlled relief valves have also been used. At the opposite end of the rotor the ordinary means is, of course, to merely drain the slip fluid into the outer casing surrounding the reactance elements etc.

The usual difliculty has been that if the space at the free end of the pintle is closed or the relief means very strong or subject to locking stoppage or sticking, then excessive pressures built up at the free end of the pintle pushes the pintle out of position with respect to the supporting casing or housing. Most pintles for this reason are made so that they will be pressed out of position when such forces as just described are set up, to prevent wrecking of the pump. I have found that it is possible to use very small clearances between the working surfaces of the pintle and barrel, to rigidly mount the pintle so that it cannot be moved axially out of the casing, and to completely enclose the free end of the pintle in the barrel and at the same time produce practically complete hydrostatic balance between the working surfaces of the pintle and rotor all along and around these surfaces by axially feeding the working fluid, or fluid at pressures proportional thereto, to the closed space between the free end of the pintle and the rotor, maintaining communication at all times between the closed space and the pressure or delivery side of the pump e. g. The fluid delivered to the working surfaces in this way apparently naturally tends to become equalized about the pintle surfaces on all sides and the resultant moving film between said working surfaces constantly replenishes the film lost by suction and apparently maintains the same film thickness on all sides so long as the pump is delivering fluid under pressure. At least this action takes place to such an extent that the troubles I have heretofore experienced (seizure, air suction, excessive bearing loads etc.) are reduced to insigniflcance. The means employed to accomplish the above may, of course, be greatly modified, but the illustrated means will now be described.

Referring to Figs. 3, 4 and 5, the main outlet and/or inlet valve ports of the pintle are indicated at II and 8|. These are of substantially conventional shape and are positioned on opposite sides of the working surfaces of the pintle substantially centrally of the tapered working portion I! as shown. The ports align successively with the reduced passages 36' of the pistoncyl nders, twoorthree of such passages being in communication with both ports at all times in the case of a five piston pump such as shown.

Let us suppose the valve port 80 is, due to the setting of the reactance assembly, the suction port and the port 8| the pressure port. Fluid is fed to the suction port through axial passages 80' on one side of the pintle communicating with a lateral main passage 80" in the enclosed end ll of the pintle. Likewise, the fluid under pressure delivered by the pump is communicated with a lateral main 8!" through a pair of axial passages 8|. With this arrangement the fluid to supply the reservoir 2i between the surfaces Ill and 20' Fig. 1, is conveyed by a central small passage which passage may run the entire length of the pintle and be communicated with the pressure side of the pump in many ways. This communication is diagrammatically indicated in Figs. 3 and 6 by a connecting pipe 86 communicating the pressure outlet 8|" with the passage 85. Actually, it is just as convenient to arrange selective communication with either the pressure or suction mains outside of the pump and a suitable arrangement is shown in Figs. 16 and 17 permitting reversal of the pump. Here the suction, e. g., passage 80" diagrammatically shown, communicates with a conduit 90 connecting the main 80" with-say one end of a piston cylinder Bi-in which is operatively mounted a piston 92 (the work) Asuitable line 93 communicates the lateral main 8i" with the opposite end of the cylinder 9| Thus by suitably controlling the reactance assembly, the piston 92 may be driven upwardly so long as the passage 8|" is on the pressure side and, by reversing the reactance assembly, the piston may then be driven downwardly, the transverse main 80" then becoming the pressure outlet. This is the conventional arrangement for heavy presses, breaches, milling machines etc. and is shown merely byway of example.

To automatically connect the central passage 85 with the pressure line, at each reversal of pump operation, a suitable double acting check valve 95 may be used in the relationship indicated in Fig. 16, this having branch conduits Si and 91 leading to the conduits SI and 93 respectively and a third branch 98 leading to 85. As shown in Fig. 17, the branch 98 communicates with a central space 98 of the valve body and both lines 96 and 51 are normally closed as by ball checks M0 and HH having a common operating spring Hi2 as shown. Whenever the line 9| is carrying the pressure fluid from the pump the check llll releases fluid from 90 to 98 and the same pressure seals the check Ill. The reverse action takes place when 93 becomes the pressure side and the check lfll is released and l Ill sealed. This same double acting check valve arrangement could, of course, be built into the pintle as at the broken ,line indication I03, Fig. 3, and probably would be in the case of large pumps.

The fluid chamber or space 2| into which the passage 85 delivers the fluid at working pump pressure may be of variable capacity as illustrated in Fig. 18. Here an axial extension of the space is provided at lla. in the form of a cylinder for a piston or plunger "5 normally acted on by'a heavy compression spring IIG to maintain the plunger against the abutment ring I". The spring is of such strength and coil capacity (preferably morecolls than as shown) that under average operating pressures of the pump the plunger is forced to the outer end of the cylindrical space 2 la where it encounters a suitable abut ment ID! or special seal to prevent leakage, as

desired. To prevent air lock and to discharge any fluid which may slip past the plunger, the coil fluid in the bore 85 after the pump no longer supplies pressure fluid therethrough to the spaces 2| and 21a. The device operates to maintain substantially constant pressure on the stored fluid in the space 2-ia whenever the pump ceases to maintain pressure in either main (as when the reactance assembly is shifted to concentric. n'on-, pumping position) so that the working surfaces of the pintle and barrel are continuously supplied with fiuid'film for lubrication, sealing, etc., during a considerable period of time.

Referring again to Fig. 1 and Figs. 3 to 15,'it. is obvious that since, the pressure exerted-by the fluid entrained'in the space-2| is equal 'in all directions and since the smaller pilot bearing l1 etc. mechanically holds the "free", or "inner end of the pintle truly centrally of theadjacent bore surfaces of the rotor or barrel, the fluid film will initially flow past the pilot bearing between the rollers into the slight working clearance space continuously all around the pintle and exert constant uniform centering forces on both the pintle and barrel all along the working surface of the pintle (except .over or immediately adjacent the suction port areas) as indicated by the small radial arrows in Figs. 10 and 13 and corresponding parallel (vertical) arrows in Figs. 9'

and 12 respectively. Thiscontinuous film movement along the pintle, toward the left in all figures, is assisted by centrifugal force due to the slight taper. This centering action is more certain to uniformly obtain at the smaller end of the pintle, i. e., before the continuous film sheet reaches the zone of the ports, but since the hydro- 4 static pressure at the pressure port and adjacent bridges is the same as-that of the oncoming film and the. rotor motion tends to spread the film all around the working surfaces and the film loss at the suction port is replenished by the opposite pressure port, substantially the same condition as above described alsoobtains on the working surfaces-beyond the valve ports, centrifugal force again acting to assist. the film movement toward the final point of discharge into atmospheric pressure (at the pilot bearing l'l, discharge being between the needle rollers). A

The continuous constant pressure of course,. most needed at the small end because this is most apt to deflect and, further, if deflection of this end can be prevented, no serious trouble is likely todevelop at theworking portiontoward the supported end from the "ports; principally on account of the rigid support for this end which is, of course, coaxial with the left hand rotor bearing supportingsurface in the casing. The'larger pilot bearing I] etc.,is also of great assistance in maintaining continuous workingclearance' at'the larger end, this being carriedon an enlarged portion of the pintle which issubject to practically no deflection; The left hand end' of the rotor is really carried on the rigid and of the pintle inoperative effect so far.

as radial load tending to displace the-rotor is concerned. v, At the pressure port areas and bridges (between .the ports) the hydrostatic forces are 'as previously described for'the general working surfaces, Fig. 8 showing (by small arrows) the radial forces at the pressure port of the pintle and Fig. simi larly showing the true balanced condition at the bridges. Thus only thesuction port area (marked with a minus sign in Fig. 11 which shows a despring housing space may be suitably vented as by transverse passages I08. The double check valve,

previously described, will prevent back-flow ofvelopment of the entire working surface of the pintle) is out of balance and this area is but a small portion (about 5%) of the whole, the remaining 95% being in hydrostatic balance.

The radial forces, as indicated by small arrows V on Fig. 15 at the cylinder inlets andoutlets,

would, of course, vary in accordance withlthe number of piston cylinders communicating at a given time with the inlet and outlet ports of the pintle but here again, as shown by the develop ment of the interior working-surface of the barrel bore, the actual: port areas are so small in comparison to the total working area; that anyheavy duty machine havingnitrided nitralloy pintle and rotor'with highly finished surfaces and very close clearance, no scoring or seizures were experienced notwithstanding the tendency theretoward due to the molecular attraction of identical smooth metallic surfaces, for each other. It will also be seen that due to preventing escapage of slip fluid at the free end of the pintle, the machine will function at' much greater efliciency since'the normal'slip. loss is reduced. to nearly one half its usual volume particularly if the working surfaces are only slightly tapered or are cylindrical. The slip fluid for lubrication and sealing has now but one main avenue of escape, namely; at the supported end of the pintle,

whereas it formerly had two and at one of these,

the loss was accentuated due to the use of centrifugal pump element as drains.

The reduction of load on the rotor or piston It is clear thatif the hydrostatic barrel bearings, due to the practice of my inven'tion, is apparent without-requiring detailed Y discussion. I A 4. forces around and along the pintle and barrel working surfaces could be completely balanced the rotor supporting. bearings would then merely have to withstand the normal torque forces and axial thrust. The present arrangement approaches veryclosely this ideal condition.

I claim '1. In a hydraulic type, including apressure line, a valve pintle, a piston barrel having a' bore in telescoping relation to the pintle, an expansible and contractible fluid tight' chamber communicating with said bore and with the pressure line of the device to supply fluid to 'said chamber for discharge thereof between theworking surfaces "of the pintle and barrel toward the opposite end of the pintle; and.

device of the radial piston check valve means to retain fluid in the elastic chamber during operation of the device and-toconstrain the same from returning to the pres,- sure line" inv the event of there being greatly reduced or negative pressure in said line.

2. In a hydraulic device including an operating pressure line, a casin'g,'a rotor. having an axial valve bore, a valve'pi'ntle-irigidl'y supported by "one end in the casing and extending fromthe supported end into said bore and terminating at its opposite end within the bore, said pintle and borefltting' with positive radial clearance about their entire circumferences, the end of the bore adjacent said opposite end of the pintle being fluid tight, said opposite end of the pintle and said fluid tight end of the bore defining a chamber for fluid, supply means freely vented into the chamber for supplying fluid at substantially normal line pressure from the operating pressure line of the device into said chamber during operation of the device, and said chamber being fluid tight except for said supply means and the clearance space between the pintle and bore wall, needle rollers interposed between the pintle and barrel bore and constraining the pintle and barrel bore to positions wherein said clearance is circumferentially uniform for causing the fluid to enter instantaneously around the entire pintle and fill the clearance space for effecting hydraulic balance of the pintle, and antifriction means between the casing and barrel for resisting axial thrust on the barrel.

3. In a hydraulic device of the character described, a rotor having an axial valve bore, cylinders communicating therewith, pistons reciprocable in the cylinders, reactance means for the pistons, a valve pintle having ports for valving cooperation with the cylinders, said pintle being received in the rotor bore with slight positive radial clearance, an expansible and contractible chamber in the rotor communicating with the valve bore, means for introducing working fluid from the operating pressure fluid circuit of the device at the normal working pressure thereof into said chamber and said clearance space and for maintaining a continuous supply of said fluid into said space during operation of the device,

and means in said chamber for automatically and positively continuing said supply of fluid from the chamber at substantially the same pressure during subsequent non-operating periods of the device and accompanying decrease in the pressure in the operating circuit.

4. In a rotary hydraulic device of the class described, a casing having a removable end cover, a tapered valve pintle mounted in the casing, a rotatable barrel having an axial bore tapered complementarily to the pintle, said pintle being received in said bore, bearing means between the barrel and pintle for maintaining said pintle and the wall of said bore in accurate coaxial relation with circumferentially uniform positive radial clearance therebetween while permitting axial adjustment of the barrel to vary said clearance space, adjustment means for adjusting the barrel axially, said adjustment means comprising an anti-friction bearing interposed between the barrel and cover, means detachably securing the cover to the casing whereby thrusts on the barrel are transferred to the cover by the bearing, and means for adjusting said end cover axially of the axis of rotation of the barrel.

J. In a radial piston type apparatus of the character described, a casing; a stationary pintle supported in said casing; a barrel having a bore receiving said pintle; piston and cylinder assemblies carried by the barrel; spaced bearings interposed between the barrel bore and the pintle and positively mechanically constraining the barrel and pintle to relative positions wherein'circumferentially uniform hydraulic fit radial clearance between the pintle and barrel bore is provided along the pintle from one of said spaced bearings to the other; high pressure and low pressure passage bores in said pintle; ports respectively commuhicating with said bores and opening through said pintle into said radial clearance between said spaced bearings, the surface of said pintle intervening between said spaced bearings being uninterrupted except for said ports; a fluid-tight chamber between one end face of the pintle and said barrel; and means exclusive of said radial clearance and always in communication with the high pressure pintle passage and opening directly into said chamber for feeding fluid at high pressure to said chamber and thereby continuously supplying fluid from said chamber to said radial clearance from said end face'of the pintle inwardly toward the opposite end to maintain said radial clearance filled with fluid under uniform pressure all around the pintle, whereby fluid pressures acting on the surface of the pintle and the barrel bore are substantially balanced, said radial clearance being the sole means for egress of fluid from said chamber.

6. In a reversible radial piston type apparatus of the character described, a casing; a stationary pintle supported in said casing; a barrel having a bore receiving said pintle; piston and cylinder assemblies carried by the barrel; spaced bearings interposed between the barrel bore and the pintle and positively mechanically constraining the barrel and pintle to relative positions wherein circumferentially uniform hydraulic fit radial clearance between the pintle and barrel bore is provided along the pintle from one of said spaced bearings to the other; high pressure and low pressure passage bores in said pintle; ports respectively communicating with said bores and opening through said pintle into said radial clearance between said spaced bearings, the surface of said pintle intervening between said spaced bearings being uninterrupted except for said ports; a fluid-tight chamber between one end face of the pintle and said barrel; and means exclusive of 'said radial clearance and always in communication with the instantaneous high pressure pintle passage and opening directly into said chamber for feeding fluid at high pressure to said chamber nothwithstanding reversals of flow through said passage bores and thereby continuously supplying fluid from said chamber to said radial clearance from said end face of the pintle inwardly toward the opposite end to maintain said radial clearance filled with fluid under uniform pressure all around the pintle, whereby fluid pressures acting on the surface of the pintle and the barrel bore are substantially balanced,

said radial clearance being the sole means for egress of fluid from said chamber.

ELEK K. BENEDEK.

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