US 2689532 A
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Description (OCR text may contain errors)
Sept. 21, 1954 Filed Jan. 9, 1951 E. ORSHANSKY, JR
NONROTATING MULTIFISTON RADIAL PUMP 4 Sheehs-Sheet 1 Sept. 21, 1954 E. ORSHANSKY, JR
Filed Jan. 9, 1951 4 Sheets-Sheet 2 32 0 1114 a 50 67(60 1 4 a lad/ 17 17 UK I 19 i9 i2 47 54 .54 V g;
fijz'as Ora/zazzs/iyJn P 1954 E. ORSHANSKY, JR 2,689,532
NONROTATING MULTIPISTON RADIAL PUMP Filed Jan. 9, 1951 4 Sheets-Sheet 3 [UVEHi C I' E4205 Ora/zazaslgydm Sept. 21, 1954 E. ORSHANSKY, JR 2,639,532
NONROTATING MULTIPISTON RADIAL PUMP Filed Jan. 9, 1951 4 Sheets-Sheet 4 Patented Sept 21, 1954 N ONROTA'I'ING MULTIPISTON RADIAL PUMP Elias Orshansky, Jr., Pasadena, Calif., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application January 9, 1951, Serial No. 205,050
4 Claims. 1 The present invention relates to a non-rotating multi-piston radial pump. More particularly, the present invention concerns a radial pump having a plurality of non-rotatable pistons actuated by an eccentrically rotatable hub and sup plied with working fluid by cam-actuated valve means.
Various types of radial pumps have been proposed in the art, particularly for utilization in high pressure hydraulic systems. However, a problem common to all such pumps has been the control of working fluid flow to and from the piston pressure spaces. The valving arrangements of the prior art have been complex, and generally have required intricate, close tolerance machining. For example, one of the more commoh types of valving arrangements involves the provision of inlet and outlet passages in a fixed pintle, and the employment of a rotatable barrel mounted on the pintle and carrying the reciprocable pistons thereon for valving coaction with the pintle passages. Thisarrangement has been unsuitable for use at relatively high pressures, due to the extreme accuracy required in machining the pintle and the barrel, and the ever present problem of working fluid leakage therebetween.
The present invention now provides an ex-,
tremely simple, readily utilized, and easily manufactured and maintained multi-piston radial pump. In the pump of the present invention, a cylinder block is fixedly positioned within a casing, the cylinder block having interior pressure spaces within which reciprocable, non-rotatable pistons are adapted for movement. Reciprocation of the pistons is carried out by a hub which is rotatable within the cylinder block and which is provided with a peripheral eccentric surface operably connected to thepistons.
The casing is provided with a pair of inwardly opening, concentric, annular fluid passages, one of the passages communicating with an inlet port for the reception of working fluid, and the other passage communicating with an outlet port for the reception of working fluid under pressure from the piston spaces. The cylinder block is provided with. fluid flow ports, each of which communicates with one of the passages of the casing, and double-acting valves are also carried by the cylinder blockfor controlling flow from the fluid flow passages into the piston chambers. These double-acting valves are controlled by rotatable valve plates which are synchronized with rotation of the eccentric hub surface, and the valve plates have camming faces which act upon the valves to reciprocate the same to establish and interrupt communication of the piston chambers with the inlet passage and the outlet passage in succession.
In this manner, rotation of the hub controls both ingress and egress of working fluid to the piston chambers, and also the subjection of the working fluid to piston pressures. control insures absolute synchronization of piston movement and working fluid communication with the piston chambers.
It is, therefore, an important object of the present invention to provide an economical, simple, radial piston pump provided with cam- :actuated valving means.
Another important object of the present invention is to provide a radial piston pump provided with non-rotatable pistons and valve means which are synchronized for operative movement by rotation of an eccentric hub.
A further important object of the present invention is to provide an improved radial piston pump having annular working fluid flow passages communicating with pump piston chambers through double-acting cam-actuated valves journaled for reciprocating movement in a piston cylinder block.
It is still another important object of the present invention to provide a radial piston pump wherein a single rotatable element coordinates and synchronizes piston pressure movement and valve actuation for fluid inlet and outlet flow.
Yet an additional object of the present invention is the provision of a radial piston pump having a rotatable eccentric hub for actuating a plurality of fluid pressure pistons and for effecting the rotation of cam actuating plates for a corresponding number of double-acting inlet and outlet fluid flow valves.
Other and further important objects of this invention will be apparent from the disclosures in the specification and the accompanying drawings.
On the drawings:
Figure 1 is a radial sectional view, with parts shown in elevation, taken along a pair of parallel axially spaced planes of a radial piston pump of the present invention;
Figure 2 is a vertical sectional view taken along the planes lIII of Figure 1;
Figure 3 is a horizontal sectional view taken along the planes IIIIII of Figure 1;
Figure 4 is a fragmentary sectional view, with parts shown in elevation, similar to Figure 3 and illustrating a double-acting valve element in neural position;
This positive Figure 5 is an exploded fragmentary perspective view, partly in section, illustrating a portion of the piston actuating mechanism of a pump of the present invention;
Figure 6 is a longitudinal sectional view, with parts shown in elevation, of a modified form of radial piston pump of the present invention; and
Figure '7 is a sectional view of the pump of Figure 6 taken along the planes VIIVII.
As shown on the drawings:
One form of pump of the present invention is illustrated in Figures 1-5, inclusive, and this form shall be described first in detail.
The pump casing and hub structure As shown in Figures 1-3, inclusive, the pump of the present invention is indicated in general by reference numeral ID, the pump including a central, generally cylindrical casing section i I closed at each axial end by front and rear cover plates l2 and 53, respectively. As particularly illustrated, the central casing section H is provided with annular end faces M and I5 each provided with circumferentially spaced, inwardly extending threaded apertures it for receiving screws ll for securing the end plates 52, #3, respectively, thereto.
The end plates l2 and 13 are each provided with inwardly extending shoulders it which snugly contact the inner periphery of the central casing section l i, and which are grooved to retain annular seal rings is against the central casing section to define a sealed inner space it lying between the plates. The central casing section i i is provided with an annular inlet groove 25 and an annular outlet groove 22 each formed in the inner periphery of the casing section ii to provide passages for a working fluid or a hydraulic medium to be utilized in connection with the pump H3, and that portion of the circumference of the central casing section 5 i lying between the grooves 2 l 22 is tapered, as at 23, to provide an inner frusto-conical bottoming surface, for a purpose to be hereinafter more fully explained.
As best seen in Figure l, the grove 22 communicates with an outlet opening 24 formed in an upstanding embossment 26 integrally cast or formed in the central casing section I I. A similar opening 2? is provided for communication with the in let groove 2 i.
The end plates 52 and it are provided with centrally located inwardly projecting annular bosses 2S and 23, respectively, which extend into the space 253 and which receive therein a press-fitted outer bearing race 33, The bearing races 33 are each in running contact with a plurality of roller bearing elements 3| which in turn contact inner bearing races 32. The bearings carried by the bosses Z8 and 29 are of substantially the same size,
and a pump hub 33 is rotatably journaled in the bearings.
The hub 33 is provided with generally cylindrical end portions 34 which contact the inner periphery of the inner bearings race 32, so that the radially enlarged central hub section is positioned between the bearings in the space 20. The central portion of the hub 33 is provided with .an eccentric outer surface 35, and the hub 33 is also provided with a central bore 36 closed at one end, namely that end adjacent the end plate l3 by a generally cylindrical hub plug 37 having a circumferential groove within which a seal ring 38 is positioned. The plug 31 is bott'omed against a shoulder 39 formed in the hub bore and is retained thereagainst by means of an annular locking ring 40. The other extremity of the hub bore 36 has extending thereinto peripherally spaced, axially elongated splines 4| for attachment to a prime mover drive shaft (not shown) or other suitable source of power. Excessive axial movement of the hub 33 relative to the bearing races 32 is prevented by means of lock nuts 42 threaded upon correspondingly threaded exterior portions of the hub.
That portion of the hub bore 36 carrying the splines 4| is surrounded by a centrally located axially outwardly extending boss l3 formed on the cover plate [2 and provided with an inwardly projecting circumferential flange lid. The
" hub 43' and the flange 44 serve to retain a pressfitted oil seal 43 in snugly seated relation be tween the cover plate I2 and the adjacent extreme end of the hub 33.
It will thus be seen that the casing sections ll, l2 and I3, cooperate to define the interior space which is sealed, as by seal rings [9, from the atmosphere. The cover plates i2 and it serve to journal therein an interiorly splined pump hub 33 having an interior eccentric camming surface 35. Upon rotation of the hub 33, any axial thrust of the hub will be taken up by the thrust bearings provided by the inner and outer races and 32 and the rollers or other anti-friction elements 3! therebetween.
Cylinder block and piston structure The rotatable hub 33 has the central eccentric surface thereof enclosed within a generally cylindrical reactance ring 31, the reactance ring and the hub surface 35 having interposed therebetween a plurality of needle bearings 48 providing an anti-friction mounting for the ring. The ring 41 has its inner periphery centrally recessed, as at 49, to accommodate the interposing of the needle bearings G3.
The outer periphery of the reactance ring 41 is contacted by a plurality of piston slipper blocks 50, perhaps best shown in Figure 5. The slipper blocks 50 are provided with curved undersurfaces 5| concentric with and mating with the outer surface 41a of the reactance ring ii. Each of the slipper blocks 50 is centrally apertured, as at 52, to receive therethrough a connecting pin 53, and each block is provided with an inner lateral extension 54 projecting laterally beyond the pin 53 to increase the surface contact of the slipper block with the reactance ring, while accommodating the positioning of an annular retaining ring 55 so as to contact each axial end of each of the pins 53.
There is a pair of spaced slipper blocks 50 associated with each pin 53, and a pair of retaining rings 55 is likewise associated with the pins 53, so that this subassembly is symmetrical on each side of the pin. The space between each pair of slipper blocks 50 accommodates the insertion of a lower portion 56 of a piston El there between. The portion 56 of the piston is apertured, as at 58, to receive the pin 53 therethrough, While the slipper blocks 50 accommodate the pin 53 in a running fit, so that rotation of the pin within the slipper blocks is accommodated upon relative movement of the piston-pin subassembly. The outer portion of each piston 57 is generally cylindrical in a configuration (Figure 1) and each piston extends into a generally cylindrical piston chamber 5% formed in the cylinder block 60 which surrounds the reactance ring 41. The cylinder block Gil is thus provided with a plurality of radially extending piston chambers 59, and each piston chamber 59 is isolated from the adjacent piston chamber so that an independent working area is provided for each piston.
The cylinder block 60 is also provided with a plurality of valving recesses 62 at the outer periphery thereof, these valving recesses being centrally located withrespect tothe axial length of the cylinder block, and each being positioned immediately adjacent asingle associated piston chamber with which the valving recess is in full communication, for a purpose to be hereinafter more fully described. On each side of each of the central valving chambers 61, the cylinder block is provided with a peripheral, arcuate valving recess 62, each valving recess 62 being in communication with the inlet and outlet annular grooves 20 and 22, respectively, and also being in communication with a valving crosspassage 53 establishing communication between the valving recesses 62 and the valving chambers 5|. Each valving passage 63 is generally cylindrical and extends axially throughout the entire axial dimension of the cylinder block.
The cylinder block 50 has a central exterior frusto-conical peripheral surface 54 which mates with and conforms to the frusto-conical surface 23 formed in the central casing section II. The extreme axial ends of the cylinder block also contact the central casing section H, as at 65, and the mating frusto-conical surfaces 23 and 64 are urged together by a cylindrical spacing element 66 interposed between the casing closure plate I 2 and the cylinder block 60. Thus, the cylinder block is firmly wedged into fixed position within the central casing section II by means of the mating frusto-conical surfaces 23-64 and the spacer block 66 acting thereon.
The cylinder block at its inner periphery is recessed to provide a relatively narrow annular land 90 projecting inwardly toward the reactance member 41 and. recessed at spaced points to provide the inner portions of the piston chambers 59. This land supports the pistons 58 against displacement under side thrusts generated by the eccentricity of the reactance member 47. Since the land 90 thus supports the pistons, an elongated radial supporting surface is provided without enlargement of the cylinder block. The narrow land 90 also accommodates radial movement of the retaining rings 55 on either side thereof.
Valuing structure As best seen in Figures 3 and 4, the hub 33, immediately adjacent the eccentric surface 35 and on each side thereof, is provided with a splined exterior surface 67, each splined surface 51 receiving thereon a valve plate 58 having a central aperture receiving the hub reduced portions 34 therebetween and having interior splines engaged with the spline surfaces 61 of the hub 33. The
plates 68 are thus positioned on each side, of the eccentric surface 35 and the plates have central web portions extending radially outwardly alongside the connecting pins 53, the slipper blocks 50, and the retaining rings 55. The web portions of the plates 68 carry facing wear plates 68 which contact the retaining ring which serve to urge the same inwardly to retain the connecting pins 53 in their axial position within the apertures 52 of the complementary slipper blocks 5! The outer peripheral portionsof the plates 58 are offset, as at 59a, to provide outer peripheral flanges having inner shoulders 70. The flanges 69a, and particularly theshoulders Ill, define a 6, rotary camming surface, inasmuch as the shoulders are inclined to a radial plane of the hub 33. Since the plates 68 are splined to the hub 33, the plates and the hub rotate as a unit, and rotation of the plates 53 causes a wobble-plate action to occour inasmuch as the flanges $9 at any given point in the space 20 will move axially of the hub 33 as the plate is rotated. This wobble-- plate action is utilized to control the valving of the pump of the present invention, and the plates 53 are indexed relative to one another so that the traveling flanges 58 of the pair of plates are always parallel with one another. In other words, a constant distance between the flanges 59 is maintained despite rotation and wobbling action of the plates 58.
The valving elements which are controlled by the plates 63 are indicated generally at H and these elements take the form of dumbbell-shaped members having a central joining portion 12, enlarged valving heads 13 at each end of the central portion 72, and terminal rounded projections M. Each valving element 1! is mounted in a cross passage 83 for reciprocation therein and the length of the central portion 12 is slightly less than the distance between the valving recesses 62, as shown in Figure 4. Each valve head T3 is of substantially the same dimension as the associated cross passage 63, and when the valving element H is in a central position, as shown in Figure 4, the valving heads 13 prevent the ingress or egress of working fluid from the inlet and outlet passages 2| and 22 to the associated piston chamber 59. The rounded projections 74 are each received by a valve plate slipper block 15 which is bottomed against the shoulder Til formed in the adjacent valve plate flange 69a. The valve plate slipper blocks 15 may preferably be formed of a bearing material, so that slippage between the flanges 69 and the blocks is accommodated upon rotation of the plates 68. The valve elements H are held within the cylinder block 65 against rotation and the projections 14 similarly hold the slipper blocks 15, while the curved contact between the projections 14 and the slipper blocks accommodates pivoting of the blocks relative to the valving element, as will be necessary upon rotation of the plates 68. Further, the shoulders m are materially longer than the corresponding diniension of the blocks 75 to accommodate radial sliding, thus preventing binding of the valve plates 68. i
The valving elements H are reeiprocable within the cross passages 63, and it will be seen from Figure 3 that the plates 68 will cause opening of the elements H to establish communication between the valving recesses 52 and the cross passages 53 or, in other words, to establish communication between the inlet passage 2! or the outlet passage 22 and a valving chamber 5|. Direct selective communication is established between the inlet and outlet passages and the piston chamber 58 so that a direct, synchronized control over the ingress and egress of working fluid'is obtained. In order to insure proper registry of the valving elements 7! with the passages 62, the hub 33 can be moved axially of the cylinder bloclc 6G by the insertion of shims between the end plates 12 and I 3 and the central casing section II.
The modified form of Figures 6 and 7 The modified form of pump illustrated in Figures 6 and 7 is a relatively small, hand-operated model which, while operating in accord ance with the principles hereinbefore set forth in connection with the embodiment of Figures l-5, inclusive, is much simpler in manufacture and operation, particularly since relatively high pressures are not generated by utilization of this form of pump.
. As. an aid in the functional description of Figures 6 and 7, reference numerals identical with those employed in the description of the embodiment of Figures 1-5, inclusive, are utilized with alphabetical suffixes attached to indicate the modified form of these parts shown in Figures 6 and '7.
The modified form of pump is indicated generally by reference numeral Illa, and it will be seen that the central casing section Ila is closed at one end by an exteriorly threaded end cap I3a carrying a seal ring [3a for sealing the interior space 20a defined within the casing. The other end cap lEa secured thereto by suitable means, with an elongated terminal boss Bil closed by an end cap 12a secured thereto by suitable means, as by screws Ha.
The pump Ilia is provided with an axially extending hub in the form of a shaft 33a, which is the functional equivalent of the hub 33 of the pump It hereinbefore described. The shaft 33a is journaled in the casing by means of bearings spaced along the length of the shaft, one of the bearings having its outer race scamounted in the end cap Ila for retaining bearing elements Bid in contact with an inner race 32a contacting an adjacent peripheral surface of the shaft. The other hearing has its outer race 30a contacting the inner periphery of a radially inward shoulder 8| formed in the central casting section I la to contact bearings elements 31 a interposed between the race 322a and an inner race 32a carrying an adjacent portion of the shaft 33d. Oil seals 45a are positioned axially outwardly of the bearings for sealing the space 20a. within the casing.
The shaft 33 is provided with a central peripheral eccentric surface 35a carrying a reactance member i'ic thereon with roller bearing members Mia being interposed therebetween. A cylinder block Sta receives the reactance member therein, the cylinder block 36a being provided with piston chambers 59a receiving therein pistons 57a for radial reciprocating movement upon rotation of the shaft 33a. The pistons El a are provided with an open-topped, generally cylindrical recesses Tb receiving springs 51c interposed between the bottom of the recesses 51b and the adjacent portion of the inner periphery of the central casing section I la. Thus, the springs 53c serve to urge the pistons 57a downwardly within the piston chambers 53a of the cylinder block 60a. toward the reactance member Ma. The cylinder block 60a is retained in axially fixed, ncn-rotative position within the casing space 23a by means of spacer rings 36d on either side thereof and wedged between a shoulder 8| formed in the central casing section [Ia and the cylinder block and between the cylindler block and the threaded closure plate I311.
The central casing portion I la is provided with an inlet opening 24a and a discharge opening 21a in full registry with annular inlet and outlet grooves 22a and 21a, respectively. The cylinder block. Eda is provided with peripheral, arcuately bottomed valving chambers 6m identical with the chambers 61 hereinbefore described and in communication with the piston bores 59a and with valving passages 63a communicating with valving recesses 62c, which in turn are in full communication with the outlet and inlet passages 8. 21a and 22a, respectively. Communication between the recesses 620; and the chambers fila is controlled by means of dumbbell-shaped valving elements Ha having end portions 14a substantially filling the passages 63a for controlling fluid communication of the passages GM with the recesses 62a. The valve elements "Ha are each provided with a reduced central portion 12a for accommodating communication between the passages at the recesses as hereinbefore described in connection with the embodiment of Figures 1-3, inclusive.
Reciprocation of the valve elements I la is accomplished by means of radially inclined bearings 82 having their inner races 83 press-fitted into recesses formed in a bearing ring 34 which is keyed to the shaft 33a, as at 85, on either side of the cylinder block 60a. Thus, the bearings 82 are rotatable with the shaft 33a, and upon such rotation a wobble-plate action is obtained which is identical with the action of the valve plates 65 of the embodiment heretofore described.
Actuation of the shaft 33a is accomplished by means of a manually-actuatable handle 83 provided with a terminal knob 87, so that the shaft 33 may be manually rotated to effect reciprocation of the pistons 51a and actuation of the valves 'Ha as hereinbefore explained.
Operation The operation of both embodiments of the pumps as hereinbefore explained will be readily evident to those skilled in the art from the disclosed structure.
Initially, it will be noted that the cylinder block 6E3 is fixed against rotation and that the pistons 51 are likewise non-rotatable but are reciprocable within the piston chambers 59 provided by the cylinder block. The pistons are pivotally linked to slipper blocks 50 which are in direct elongated contact with a reactance member 41 and, in the second embodiment of the invention, the pistons 5'1 may directly contact the reactance member Mb. The reactance member is disposed in encircling relation upon the eccentric cam surface 35 of the hub 33 or shaft 33a, and rotation of the eccentric member will cause radial movement of the reactance member to actuate the pistons in a radial direction within the cylinder block piston chambers.
The piston chambers 59 are in valved communication with the annular inlet and outlet chambers or grooves 22 and 2!, respectively, so that communication between the fluid flow passages and the piston chambers could be accommodated at any time if it were not for the unique valving arrangement of the present invention.
The valving arrangement includes the doubleacting valve H which are fixed against rotation, inasmuch as the valves are journaled in the cross-passages 63. Reciprocation of the valves serves to alternately connect the cross-passages 63 and eventually the piston chambers with the inlet and outlet by means of camming surfaces which are rotatable with the piston-actuating ec centric member, the hub 33', or the shaft 33a. The camming surfaces of the valving plates affect a complete reciprocation cycle of each of the valve elements H during each revolution of the hub 33 and each intake and discharge cycle of the pistons 51. Thus, a very simple valving arrangement is provided with absolute synchronism between rotation of the eccentric driving member and the valving action being insured, and wear and. tear upon the valving mechanism is substantially lessened by the holding of the valves against rotation and the elimination of relatively rotatable valving surfaces.
The opposing equally sized valve heads [3 present equal inner face areas to working fluid acting thereagainst so that any working fluid pressure thrust upon the valves H is equalized and there is no differential fluid pressure force tending to force the valves in a lateral direction.
It will be understood that modifications and variations may be eflected without departing from the scope of the novel concepts of the present invention.
I claim as my invention:
1. A multi-piston radial pump comprising a casing defining a generally cylindrical interior space, a fixed generally cylindrical cylinder block in said space having radially extending piston chambers, pistons in said chambers for reciprocation therein, radially inwardly extending slipper blocks carried by said piston for reciprocation therewith, a rotatable hub having an eccentric peripheral surface acting upon said slipper blocks during rotation of the hub to reciprocate said blocks and the pistons associated therewith, said casing having spaced annular inlet and outlet fluid flow conduits formed in its inner periphery and communicating with a source of Working fluid and a working fluid pressure outlet, said cylinder block having cross-passages communicating with the casing passages and with said piston chambers, double-acting reciprocable valves slidably journaled in said cross-passages for reciprocation therein to alternately connect each of said piston chambers with the inlet and outlet passages of said casing, and annular valve plates rotatable in synchronism with said hub and having opposing camming faces inclined with respect to a radial plane of the hub and acting directly upon said valves to reciprocate the same.
2. A multi-piston radial pump comprising a casing defining a generally cylindrical block in said space having radially extending piston chambers, pistons in said chambers for reciprocation therein, radially inwardly extending slipper blocks carried by said piston for reciprocation therewith, a rotatable hub having an eccentric peripheral surface acting upon said slipper blocks during rotation of the hub to reciprocate said blocks and the pisr tons associated therewith, said casing having spaced annular inlet and outlet fluid flow conduits formed in its inner periphery and communicating with a source of working fluid and a working fluid pressure outlet, said cylinder block having cross-passages communicating with the casing passages and with said piston chambers, double acting valve means journaled in the cylinder block cross-passages for reciprocation therein, said valves having enlarged heads snugly fitting said cross-passages and terminal projections extending therebeyond, said valve heads 10 being effective to control communication between the casing passages and the piston chainbers upon reciprocation of the valves, and valve plates carried by said hub for rotation therewith and having camming surfaces inclined with respect to a radial plane of the hub for sliding engagement with the valve terminal projections to reciprocate said valves in said cross-passages.
3. In a pump, a casing, an annular cylinder block in said casing and having an integrally formed inwardly projecting reduced thickness land, said cylinder block and the land thereof having registering recesses defining a plurality of circumferentially spaced open-ended radially extending piston chambers, radial pistons in said chambers, a slipper block for each of said pistons positioned on each side of said cylinder block land, a transverse pin received by mating apertures formed in said slipper block and the associated pistons, radial movement or said pins being accommodated by said land recesses, an annular retaining ring abutting each end of each of said pins for movement therewith on each side of said land, rotatable eccentric means reciprocating said pistons, means providing peripheral inlet and outlet fluid flow passages in said block and in said casing communicating with said piston chambers, slidable valve means located in said passages for controlling flow between said piston chambers and said flow passages, and cam actuating means acting on said valve means to actuate the same in synchronism with the reciprocation of said pistons.
4. In a pump, a casing, an annular cylinder block in said casing and having an inwardly projecting reduced thickness land, said cylinder block and the land thereof having registering recesses forming a row of open-ended radially extending piston chambers, a piston in each of said chambers, rotatable eccentric driving means in said casing for reciprocating said pistons, said cylinder block land supporting said pistons against side thrusts generated by rotation of the eccentric driving means, means providing peripheral inlet and outlet fluid flow passages in said block and in said casing communicating with said piston chambers, slidable valve means located in said passages for controlling fluid flow between said piston chambers and said flow passages, and actuaing means acting on said valve means to actuate the same in. synchronism with reciprocation of said pistons.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,471,117 Orshansky May 24, 1949 FOREIGN PATENTS Number Country Date 15,221 Great Britain Aug. 13, 1895