US3043232A - Opposed rotor radial piston pumps - Google Patents

Description

July 10, 1962 R. J. POULlN 3,043,232

OPPOSED ROTOR RADIAL PISTON PUMPS Filed Jan. 22, 1958 2 Sheets-Sheet 1 FM; Ilo

20 717 g? i 13 m W -10 l9 18@ t July 10, 1962 R. J. POULIN 3,04

OPPOSED ROTOR RADIAL PISTON PUMPS Filed Jan. 22, 1958 2 Sheets-Sheet 2 I l I 36 l 3 5 39 1 7/ IN VEN TOR 3,043,232 GPPQSED RGTGR RADKAL PISTGN PUMPS Raymond J. Poulin, R0. Box 808, Topanga, Cahfl, as-

signcr of one-half to Edward H. Rose, Santa Monica,

Calif. Filed Jan. 22, 1953, Ser. No. 710,523 14 Claims. (Cl. 103-161) This invention relates to radial piston pumps and, more particularly, to an opposed rotor radial piston pump in which the pistons in each rotor are depressed by engaging the surface of the other rotor, and which is adapted to provide high volume at medium pressures.

and high pressures at low volume and requiring less power for its operation than is needed for conventional pumps.

During their operating cycles many hydraulically powered machines such as hydro presses, injection molding machines, and the like, require a large volume of fluid at medium pressure to move certain parts of the machine from one position to another and additionally, for brief periods, require peak pressures many times as great. In order to meet these requirements engineers have found it necessary to select pumps having large volume output and power them with motors having suificient horsepower to deliver the peak pressures required. This problem proves particularly difficult in the case of constant volume pumps.

. Accordingly, the use of accumulators has become common in the general art as a means for reducing the inordinately high power required in hydraulically operated machines of this type and, more recently, variable flow radial and axial piston pumps have served to further reduce the disproportionate ratio between the power required to fulfill performance requirements. However, the plunger or piston type pumps heretofore available have followed design patterns characterized by attendant problems such as the rugged construction required for high pressures and the somewhat complicated mechanisms involved in volume control that left much to be desired in simplicity and operational efficiency as well as in the operating power required.

My invention has been made with the foregoing considerations in mind, and can be said to have a plurality of important objectives.

One important object of my invention is the provision of a radial piston pump being adapted to fulfill high volume and pressure requirements on minimal operating power. 1

Another important object of my invention is the provision of a radial piston pump being adapted with opposed cylindrical rotors disposed in tangential juxtaposition whereby each rotor serves as camming means for depressing the radially disposed pistons of the other.

A further object of the present invention is the provision of a radial piston pump of the character described being adapted to provide a wide range in volume output without the employment of substantially complicated mechanical control means.

An additional object of my invention is the provision of a radial pump of the character described and being adapted in conformation whereby the amount of time and movement devoted to the inlet phase of the pumping cycle during each revolution of the rotors is several times as great as that of the exhaust phase.

Another object of my invention is the provision of a radial piston pump of the character described which is adapted with means for changing and controlling the ratio between its volume and pressure outputs.

A still further object of my invention is the provision of a radial piston pump of the character described be- Patented .iuly 10, 1962 sited rates Fatent @t tge WW2 2 ing adapted with piston actuation and fluid inlet control means being effective to substantially eliminate forced leakage around the pistons together with the friction, noise and heat generated thereby.

In brief, the opposed rotor radial piston pump of my invention includes a pair of cylindrical rotors juxtaposed in coplanar alignment, journalled on parallel stationary shafts and intergeared-for contrarotation. In each rotor is a plurality of radial bores fitted with pistons having dome-shaped heads which extend outwardly of the circumferential periphery of the rotors, and the two rotors are relatively positioned and intergeared so that the piston domes of each are alternately depressed upon engagement with the periphery of the other as the rotors revolve.

The stationary shafts which in the present embodiment are conformed in the manner of studs or pintles, are provided with inlet and exhaust ducts which open laterally of the shafts in line with the rotor bores. The exhaust ducts open in the direction of the point of contact of the two rotors, and the inlet duct-s open oppositely into channels disposed circumferentially of the shafts and terminated adjacent opposite sides of the exhaust duct openings. A pressure sensitive flow valve, introduced in the fluid supply line, serves to control the amount of fluid drawn into the bores from the inlet channels during the inlet phase of each revolution. The

pistons are provided with return springs adapted to move the pistons outwardly in the bores only as far as necessary to draw in the available fluid. Thus, reducing the inlet flow shortens the stroke of the pistons and reduces the volume output of the pump without reducing the pres-sure developed or imposing a greater load on the motor. Interchangeability of driving gears permits additional latitude in the selection of power to meet the general requirements of the machine being operated.

Other objects of my invention as well as possible variations in the form and details of the embodiment set forth will be apparent in the following specification when it is examined together with the references made therein to the accompanying drawings, of which:

EEGURE l is a frontal perspective view of an opposed rotor radial piston pump constructed according to my invention;

FIGURE 2 is a sectional view taken along a horizontal plane through the frontal gear housing disposed as seen in FIGURE 1 with the upper half of the gear housing removed to show the elements therein;

FIGURE 3 is a schematic diagram showing the manner in which the domed heads of the pistons are alternately engaged by the cylindrical periphery of the other rotor and are pressed inwardly thereby;

FIGURE 4 is a schematic diagram, similar to that of FIGURE 3, in which the rotors are segmented to indicate the proportion of each revolution devoted to the exhaust and inlet phases of the pumping cycle; 7

FIGURE 5 is a perspective diagram of one of the identical stationary shaft members showing the positions therein of the ducts directing fluid to and through the FIGURE-6 is a horizontal section taken along the lines and in the direction indicated by the arrows 6-6 in FIG- URE 5 FIGURE 7 is a diagrammatic section taken verticaHy and axially of one of the ducted shafts such as the one shown in FIGURE 5;

FIGURE 8 is a vertical section of one rotor assembly taken axially of the shaft positioned as shown in FIG- URE 2, with the housing completely removed and the ducting, which is normally provided by the housing structure, shown schematically, and

FIGURE 9 is a frontal view of a variation in the arrangement and construction structed according to my invention showing the manner in which they may be used and ducted in multiples in pumps of larger capacities. v 7

Reference is again made to FIGURE 1 in which a radial piston pump constructed according to my invention is designated generally by the numeral 10 and is seen to include a motor 1 1, a motor fan and oil cooler assembly 12, attachment. means 13, and a forwardly disposed gear housing 14 including two closure plates 15 and 16, and a frontally extended area 17 disposed forwardly of the frontal surface 18 of the plate 15 in which the inlet and exhaust hydraulic lines 19 and 20 respectively are received.

In the horizontal sectional view of FIGURE 2 the upper half of the housing 14 has been removed to more clearly indicate the relative positioning of the pump eleof the pump rotors con-' ments positioned therein. The half sections 15 and 16 V of the housing 14 are secured together by suitable fastening means such asthe machine bolts 21 and removably attached to the cooler assembly 12 by bolts such as shown at '22 in FIGURE 1.

The rotors 23 and 24 as shown in FIGURE 2 are formed integrally with the spur gears 25 and 26. The hollow member 28 which is diminished indiameter at 29 to pro-.

vide a shaft section to which the spur gear 34) is aflixed.

The pinion gear 31 which is journalled on a stud 32 extending outwardly from and integrally formed with the closure section 16, engages both the drive shaft of the power source 11 and the spur gear 30. As will be readily understood, changes in the ratios of the gears and 31 may be made to alter the speed of rotation of the rotors 23-and 24. r g The two rotors 23 and 24 including their engaging gear sections 25 and 26 and their outwardly extended drive members 27 and 28, respectively, are journalled on stationary shafts 33 and 34 which for the sake of illustrative and descriptive clarity, have been indicated as separate short shaft sections but are actually fixed to the structure and v in actual practice are formed integrally with the casing 4 vided with a circumferential shoulder as shown at from which a short shaft section 51 is extended and terminated outwardly in a domed head 52. A retaining ring 53, adapted to fit around the circumferential periphery of the piston area of the rotor 23, is provided with perforations adapted to receive slidably therein the shaft portions such as 51 and through which the pistons, such as 45, move outwardly until restrained by the shoulder sections, as indicated at 50.

As shown in FIGURE 8 the piston 45 is seen to be at the limit of outward movement during the intake phase of the pumping cycle, and the piston 46, opposite therefrom, is shown completely depressed inwardly of the cylindrical bore 44 by engagement of its domed head 54 against the outer periphery of therotor 24, fluid being supplied to the bore 43 through the inlet duct 35, and exhausted inwardly of the piston46 through the exhaust duct 38. V

The means employed for controlling the volumeoutput of the pump is also shown schematically in FIGURE 8. From the exhaust duct 38 a line indicated by the numeral 56 opens into a pressure sensitive flow valve 57 having adjustment means'indicated by the knob 58 effective to reduce the inlet flow in the inlet duct 35 to any desired degree and adjustment means calibrated in units of pressure indicated by the dial 59 for presetting the pressure at which the flow restriction becomes operative.

The control system above described permits the pump to supply a comparatively large volume outputat mod erate pressures for the purpose of moving parts of a machine from one position to another as has been previously explained, and then, as peak loads are approached, reducing the flow of inlet fluid thereby shortening the stroke of the pistons, which move outwardly in the fluid tight cylinders only as far as required to accommodate the 7 available volume of inlet fluid, thus reducing the volume section 15 in the manner of projecting studs or pintles.

'Iheir conformation will be more clearly understood by reference to the perspective view and the horizontal and vertical sectional views of the shaft 33 shown in FIGURES V 5, 6 and 7'respectively. 1

The inlet duct which is designated generally by the numeral 35 in FIGURES 5-7 is entered through the bottom of the shaft as seen at 36 and opens laterally thereof into a semicircular channel 37 which is extended circumferentially of the shaft as best seen in the sectional 'view of FIGURE 6 which is taken along the line and in the direction indicated by the arrows 6-6 in FIGURE 5.

' a The exhaust duct 38 is entered through the side of the shaft 33 as shown at 39 in FIGURES 5 and 7, and is ex- 7 tended; upwardly and opened laterally of the shaft at the aperture 40 which is disposed intermediate of the terminations 41 and 42 of the circumferential channel 37.

' Referenceis made to the vertical sectional view of FIG- URE 8 showing one of the rotor assemblies and the mannertin which the drive sleeve 27, radial piston rotor sec tion 23 and spur gear bottom portion 25 are integrally formed in a single piece journalled on the stationary shaft 33.

- Each of the'rotors 23 and 24 is provided with a plurality of radial-bores such as 43 and 44 which are clearly shown in section in FIGURE 8.

a Each of the bores such as 43 and 44 is fitted with a piston, such as 45 and 46,which includes a sleeve portion as'seen at 47 adapted to receive one end of a spring 48; the opposite end of the spring 48 being received and retained in a section 49 of the bore 43 of reduced diameter.

outwardly of' the sleeve portion 47 the piston 45 is pro- 7 output and enabling the pressure to be substantially increased without overburdem'ng the power supply.

The schematic diagram of FIGURE 3 clearly illustrates the manner in which the pistons of each rotor are alternatelydepressed upon engagement with the circumferential surface of the other rotor, and further indicates the positions of the pistons in each of the rotors and the positioning of the rotors relative to each other, and the alternate sequence of piston movement.

:In FIGURE 3 therotors 61 and 62 are shown schematically as they would appear when viewed in the direction of arrow 3 in FIGURE 2 with the closure plate 16 removed, The shafts 63 and on which the rotors are journalled are-shown cross sectionally along a plane being coincident with the axial centerlines of the radial bores, such as 43 and 44 in FIGURE 8, and of the circumferential inlet channel such as 37 in FIGURE 6. The positions of certain of the pistons within the rotors are indicated inphantom. a 1 l With the rotors revolving oppositely in the directions indicated by the arrows 65 and 66, the domed piston head v67 of the rotor 61 is seen to be partially depressed as it engages the piston retaining ring 62-R of the rotor 62, and the inner opening 68 of the radial bore 68 is partial communicating alignment with the exhaust aperture 70 of the stationary shaft 63; and simultaneously the piston 71 isseen to bemoving outwardly of the rotor 61, and the opening 72 of the radial bore 73 is beginning to overlap the inlet channel 74 which communicates with the inlet duct 75. Meanwhile the piston 76 in the bore 77 of the rotor, 62 is seen to be completely depressed inwardly and the opening 78 of the bore 77 has rotated beyond the point of axial alignment with the opening 79 of the exhaust 'duct 80 in the stationary shaft 64.

An understanding of the relatively short amount of time required for the'exhaust phase compared to theinlet phase of the pumping cycle can be obtained from the purely schematic diagram in FIGURE 4 in which each of the rotors 81 and 82 is providedwith eight pistons in- '5 dicat'ed by the domed heads '83 and 84 respectively, with the axial centerlines of the bores being indicated by the diametric lines such'as 85 and 86 with each acute angle therebetween being of forty-five degrees. It is apparent, in the diagram, that the difference in the positions of the diametric line 87 in the rotor 81 and that of the line 88 in the rotor 82 represents only 22 /2 degrees of rotation and, by reference also to FIGURE 3, that the majority of the actual discharge of fluid from the cylinder bore takes place within this span of movement. It is further apparent that if each rotor were supplied with twelve pistons, the diametric axial centerlines such as 85 and 36 would be spaced at thirty degree angles, and the discharge of one piston would be completed during each fifteen de grees of rotation of the two rotors.

For production machines requiring greater volume or higher pressures than that available from a single pair of rotors having a given number of pistons of given displacement such as has been previously described, my invention encompasses the use of a plurality of rotors as indicated schematically in FIGURE 9 wherein two rotors 89 and 90 are superposed and rotate in contact with the rotors 91 and 92. Each pair of rotors is journalled upon shafts such as that shown in vertical section at 93 in FIGURE 9. The inlet duct 94 is provided with a plurality of apertures as indicated at 95 and 96 which open into the circumferential inlet channels previously described, and the exhaust duct 97 is similarly provided with openings such as 98 and 99 which communicate with the piston bores. A further variation of this duel rotor embodiment is indicated by the fragmentary section 100 in FIGURE 9 showing the two sets of piston bores disposed in a single cylindrical section, and experiments conducted with test models indicate that the number of pistons that can be used in this manner in longer cylindrical rotors is limited only by the difficulty encountered in ducting the fluid to and from the pistons.

The invention also anticipates and encompasses substantial variation in the bore and stroke of the pistons and in the shape, length and general conformation of the outwardly extended piston heads as compared to the relative sizes implied in the illustrations of the embodiment set forth herein.

For instance, very successful results were obtained from one test prototype in which shallow circular sockets such as 101 and 102 in FIGURE 9 were provided in the piston retaining rings between each pair of piston heads, and the pistons having generally half-round heads such as that seen at 103 were replaced with pistons with ovularly conformed heads such as 104 and longer shaft sections as indicated at 105. Since the heads and sockets are complementary in conformation, each ovular head is received in its respective socket and is pressed inwardly of its bore with minimal lateral pressure as the longitudinal axes of the heads and sockets rotate into longitudinal alignment. This modification makes possible an increase in the piston stroke without measurable increase in piston or cylinder wear.

From the foregoing specification and description it will be apparent that the opposed rotor radial piston pump of 'my invention is adapted to operate smoothly and quietly since its mechanical arrangement does not involve any violent eccentric movement characteristic of the wobble plates, ofiset cylinders and eccentric rotation employed in conventional positive displacement piston type pumps.

It will also be observed that I have provided a greatly simplified pumping mechanism consisting of contrarotating circular cylinder blocks, each having a plurality of radial pistons therein and each serving as camming means for depressing the cylinders of the other.

It willbe further observed that by employing this opposed rotor arrangement the friction producing factors have been substantially reduced and I have provided a pump adapted to remain cool and efiicient during prolonged periods of operation.

I have also included means for increasing the duration of the inlet phase of the pumping cycle compared to that of the exhaust phase, and have provided a porting system which eliminates forced leakage of the fluid, a common characteristic in conventional piston type pumps.

Attention is also called to the fact that the opposed rotor radial piston pump of my invention has been shown to provide wide variations in volume output without the employment of substantially complicated mechanical control means. 7 p

it is to be noted further that I have provided a radial piston pump which is capable of fulfilling high volume and pressure requirements on a minimum of operating stricted to the embodiment set forth herein nor limited in any manner except as may be defined by the extent of the appended claims.

What I claim is:

1. A radial piston pump, comprising: a pair of cylindrical rotors having spaced parallel planar surfaces and cylindrical peripheral sidewalls therebetween, and, each having a plurality of radial bores disposed uniformly therein and each of said rotors having a spur gear portion formed integrally therewith; pistons fitting slidably within said bores and being provided with rounded heads normally extended outwardly of said cylindrical peripheral sidewalls of said rotors; said rotors being journalled on parallel shafts having fluid ducts therein, said ducts being apertured laterally of said shafts in axial alignment with said radial bores; said rotors being disposed with their respective planar surfaces in coplanar relationship and their cylindrical sidewalls substantially in tangential contact between said shafts, and with their spur gear portions in mating engagement and effective to counter-rotate said rotors and alternately depress the pistons of each of said rotors inwardly of said bores as said outwardly extended piston heads rotate into abutting contact with said cylindrical sidewall of the other rotor.

'2. A radial piston pump, comprising: a fluid tight housing; a pair of stationary shafts disposed axially parallel interiorly of said housing, said shafts having fluid ducts therein; said ducts being apertured laterally of said shafts at one end and opening outwardly of said housing at the other end; a pair of cylindrical rotors journalled on said shafts, each of said rotors having a plurality of radial bores disposed uniformly therein and opening inwardly alignment with said apertures of said ducts; pistons fitting slidably within said bores and being provided with rounded heads normally extended outwardly of the cylindrical sidewalls of said rotors; said stationary shafts being spaced apart so as to bring the cylindrical sidewalls of said rotors in substantial contact tangentially along a line parallel to the axes of said parallel shafts; said rotors having engaging spur gear portions respectively rigid therewith and effective to counter-rotate said rotors so that the pistons of each of said rotors are alternately depressed inwardly of said bores upon coming into contact with said cylindrical sidewall of the other rotor, thereby discharging through one of said ducts fluid received in said bores from the other of said ducts.

3. In a radial piston pump, the combination comprising: a pair of cylindrical rotors journalled on parallel shafts having fluid ducts therein and being spaced apart to bring the cylindrical sidewalls of said rotors into substantial contact tangentially along'a line (parallel to the axes of said shafts; said rotors having a plurality of radial gear portions integrally formed therewith; pistons fitting bores disposed uniformly therein and having engaging spur slidablywithin .said bores and having rounded heads of reduced diameter extending outwardly of said rotor sidesaid bores. r

4. A radial piston pump, comprising: a fluid' tight hous-v ing; a pair of stationary shafts disposed in axially parallel relationship interiorly of said housing; said shafts having fluid ducts therein, said ducts being apertured laterally of said shafts at one end and opening outwardly of said housing at the other end; a pair of cylindrical rotors journalled "onsaid shafts, each of said rotors having a plurality of radial bores disposed uniformly therein opening inwardly in alignment with said apertures of said ducts; pistons fitting slidably within said bores and being provided With rounded heads of diminished -diameter normally extended outwardly of thecylindrical sidewalls of said rotors; said stationary shafts being spacedapart so as to bring the cylindrical sidewallsof said rotors into tangential rolling contact 'between said parallel shafts; spring mea'ns'disposed in said bores being adapted to urge said pistons outwardly thereof; a piston retaining cylindrical band, perforated to receive said pistontheads of diminished di- 'anieter, extending around the sidewall of each of said rotors'and effective to-hold said pistons in said bores;

said rotors having engaging spur gear portions and power coupling means effective to counter-rotate 'said rotors 'whereby the pistons of each are alternately depressed inwardly of said bores upon rotating into contact'with said piston retaining band of the'othen p v 5. A radial piston pump, comprising:' a fluid tight housing; a pair of stationary shafts disposed in axially parallel relationship interiorly of said housing; said shafts having fluid ducts therein, one end of said ducts being terminated in apertures opening laterally of said shafts, the other ends'opening outwardly of said housing; a pair of cylindrical rotors journalled on said shafts, each of said'r'otors being integrally formed with a spur gear portion and having a plurality of radial bores disposed uniformly therein and opening inwardly in alignment with i said laterally opening apertures-of said ducts; pistons 1 fitting'slidably within said bores and being provided with rounded heads normally extended outwardly of the cylindrical sidewalls of said rotors; said stationary shafts being spaced apart so as to bring the cylindrical sidewalls of said rotors together in rollinglcontaet between said parallel shafts and align saidfspur geanportions thereof revolve oppositely an'd the pistons of each of said rotors t are alternately depressed inwardly of said bores upon rotating intoiabutting contact with said cylindrical sidewall of the other each piston being reciprocated during rotation of the rotors through an arc of less than fortyfive degrees. a 7

6. An opposed rotor radial piston pump, comprising a fluid tight housing: a pair of stationary shafts disposed f 'axially parallelto each other interiorly of said housing;

,pistons fitting slidably within said bores and being provided with rounded heads of diminished diameter normal-t 1y extended outwardly of the cylindrical sidewalls of inrrneshing engagement wherebys'aid rotors are oaused'to revolve oppositely and the pistons of each of said rotors 1 are alternately depressed inwardly of said bores upon rotating into abutting contact with said piston retaining band of the other, thereby discharging through one of said ducts any fluid received in said bores from another of said ducts. V v

7. The invention in accordance with claim 6 being further characterized by piston stress relieving means, comprising: said piston retaining bands being provided with shallow sockets disposed inwardly from the outer periphery of said bands and spaced intermediate of said piston heads extended therethrough; said'sockets being complementary in conformation tosaid piston heads and adapted to receive said heads movably therein.

8. A radial piston pump, comprising: a fluid-tight housing having fluid inlet and outlet apertures therein; a pair-of generally cylindrical rotors being tangentially disposed interiorly of said hou sing and being journalled on parallel shafts rigid with said housing; a plurality of radial bores uniformly'disposed in each of said rotors; pistons slidable radially within said bores, and resilient spring means disposed inwardly of said pistons in said -bores adapted to normally support said pistons with their heads extended outwardly of said bores; gear means and power coupling means being effective to contra-r0 tate said rotors; said shaftsrdefining ported pintles having axial ducts therein communicating with said inlet and outlet apertures in said housing, and opening laterally and oppositely of said pintles so as to communicate with said radial bores in said rotors. I V t i 9. A radial piston pump in accordance with claim 8 being further characterized by the amount of normal extension of said pistons outwardly of the circumference of said rotors being adapted in length relative to the space provided by the. combined angleformed by the arcs of thetwo rotors adjacent their point of tangency whereby the complete depression of a piston into a bore in one rotor, upon rotating into abutting contact with the peripheral surface of the other rotor, is effected during rotational movement of the rotors of not.more than one-sixteenth of a complete revolution, the pistons of either rotor being depressed singly, and the pistons of both rotors being depressed in alternate succession. '10. A radial piston pump including the combination of: a pairrof cylindrical rotors journalled on parallel stationary shafts spaced apart so that the cylindrical surfaces of the rotors are intangential'rolling contact; a plurality of radial bores in at least one of said rotors; pistons slidably disposed in said bores and having heads normally extended outwardly of the cylindrical surfaces of. the rotors; outwardly opening ducts disposed axially in at least one of said shafts and apertured laterally thereof so as to communicate with said bores in'said rotors; gear and power coupling means effective to counterrotate the rptors and move the heads of'the pistons 'outwardly of the rotors by centrifugal force, the pistons in either rotor being reciprocated as their outwardly extended heads rotate into contact with the cylindrical slidably disposed in said bores and having heads normally extended outwardly of the cylindrical surfaces of the rotors; outwardly opening ducts disposed axially in said shafts and apertured laterally thereof so as to communicate with the radial bores in the rotors; gear and power coupling means effective to counter-rotate the rotors and move the heads of the pistons outwardly of the rotors by centrifugal force, the pistons in either rotor being reciprocated by reason of their outwardly extended heads coming into contact with the cylindrical surface of the other rotor, each piston being reciprocated during movement of the rotors through an arc of less than forty-five degrees and being outwardly extended during the balance of each revolution of the rotors.

12. A radial piston pump including the combination of claim 11 and wherein said radial bores and pistons therein are spaced apart by the same distance on the cylindrical surface of each of said rotors.

13. A radial piston pump including the combination of: a pair of cylindrical rotors, each having an axial aperture therethrough and a plurality of radial bores therein communicating between the cylindrical sidewalls and the axial apertures; said radial bores being spaced apart by the same distance on the cylindrical sidewalls of both of said rotors; pistons slidably disposed in said radial bores and having arcuate heads normally disposed outwardly of the cylindrical sidewalls of the rotors; said rotors being journalled on axially parallel stationary shafts; inlet and exhaust ducts extending axially in and opening laterally of said shafts, said inlet ducts being adapted to communicate with a majority of said bores and said exhaust ducts being adapted to communicate with only one of said bores in each of said rotors at a time; said axially parallel shafts being spaced apart so as to bring the cylindrical sidewalls into substantial tangential rolling contact; said rotors being relatively positioned for rotation on said shafts so that their radial bores and pistons therein occur alternately at the point of tangential rolling contact of the rotors; power coupling and gear means effective to counter rotate the rotors and to maintain their rotational relationship whereby each rotor is effective to reciprocate the pistons of the other rotor upon successive rotational contact with the outwardly disposed heads thereof.

14. In combination, a radial piston pump in accordance with claim 11 and piston return springs adapted to move said pistons outwardly in said bores only as far as necessary to draw the available inlet fluid into said bores, whereby reducing the fluid inlet fiow is efifective to shorten the stroke of said pistons and thereby reduce the volume of fluid output without reducing its pressure.

References Cited in the file of this patent UNITED STATES PATENTS 573,580 Dyer Dec. 22, 1896 683,834 Beckfield Oct. 1, 1901 868,100 Krehbiel Oct. 15, 1907 1,817,370 Hammerstrorn Aug. 4, 1931 1,948,907 Egli Feb. 27, 1934 1,978,441 Suenson Oct. 30, 1934 2,044,867 Woodward June 23, 1936 2,096,907 Linderman Oct. 26, 1937 2,504,841 Jones Apr. 18, 1950 2,581,764 Leibing Jan. 8, 1952 2,612,110 Delegard Sept. 30, 1952 2,764,941 Miller et a1. Oct. 2, 1956 FOREIGN PATENTS 2,444 Great Britain Feb. 4, 1908 4,266 Great Britain Feb. 2, 1893 113,021 Switzerland Dec. 16, 1925 422,312 Italy June 13, 1947 734,001 Germany Mar. 11, 1943

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