US2650543A - High-pressure radial piston pump for liquids - Google Patents

Description

G. PAUGET HIGH-PRESSURE RADIAL PISTON PUMP FOR LIQUIDS Original Filed 001;. 23, 1945 Sept. 1, 1953 4 Sheets-Sheet 1 Sept. 1, 1953 G. PAUGET 2,650,543

HIGHPRELSSURE RADIAL PISTON PUMP FOR LIQUIDS Original Filed Oct. 23, 1945 I 4 Sheets-Sheet s p 1953 G. PAUGET HIGH-PRESSURE" RADIAL PISTON PUMP FOR'LIQUIDS Original Filed Oct. 23, 1945 4 Sheets-Sheet 4 A GE Patented Sept. 1, 1953 HIGH-PRESSURE RADIAL PISTON PUMP FOR LIQUIDS Georges Pauget, Chaville, France, assignor to Societe dlnstallation et dAppareillage, Paris, France Continuation of application Serial No. 624,028, October 23, 1945. This application October 17,

1950, Serial No. 190,539.

Claims.

This patent application is a continuation of my earlier patent application Serial No. 624,028 filed on October 23, 1945, for High pressure radial piston pumps for liquids, now abandoned, and certain parts of the present application will be found in the earlier application.

The present invention relates to improvements in pumps for liquids and in particular in high pressure radial piston pumps controlled by an eccentric keyed on a central shaft.

The principal object of the invention is to provide, in a pump of the character described, means for automatically and instantaneously discontinuing the pumping action whenever the delivery pressure thereof exceeds a predetermined value, and without necessitating a stopping of the rotation of the shaft of the pump.

A further object of the invention is to provide a structure of the above type in which the discontinuance of the pumping action is obtained by means which operates to immobilize the pistons of the pump in their outermost positions, against the pressure of the resilient means which normally urges them inwardly against the driving eccentric of the pump.

Still another object of the invention is to provide a pump of the above character in which the means for immobilizing the pistons at their outer positions comprises hydraulic elements contained entirely within the pump body and powered by the pressure fluid of the pump itself, whereby it is possible to dispense with the electrical or manometric external controls formerly employed for similar purposes, and whereby the cost and complexity of manufacture and maintenance of the pump is greatly reduced.

According to the present invention, the means for automatically and instantaneously discontinuing the pumping action or automatic checking means are hydraulically controlled by the discharge pressure of the pump so that they become operative when said pressure is in excess of a predetermined value for actuating means immobilizing the pistons in their outermost positions. Said hydraulic control is operated by a double valve having two opposite seats and which is adapted to be suddenly set in operation, one

of the chambers of the said valve being placed in communication with the pressure at delivery,

while the other chamber is placed in communication with the pressure at suction and the intermediate chamber in which moves the head of said double valve between its two seats is placed in communication with the immobilizing means. The present invention also includes a certain In France October 2 number of particular features which will appear from the following description referring to the accompanying drawings given by way of example only and wherein:

Figure 1 is an elevation view of a radial piston pump according to the invention with a general cross-section along the vertical plane of symmetry.

Figure 2 is a sectional view through line II-II of Figure 1 showing, at smaller scale, the arrangement of the hydraulic checking device.

Figure 3 is a cross sectional view taken on the line III-III of Fig. 2.

Figure 4 is a view on enlarged scale of the double valve shown in Fig. 3.

Figure 5 is an elevational outer view from the right of Fig. 1 showing the conduits discharging the liquid towards the single collector.

Figure 6 is a cross sectional view taken on the line VIVI of Fig. l at smaller scale.

Figure 7 is a sectional view taken centrally through one of the pumping units comprising an alternative embodiment of an automatic hydraulic checking device in inoperative position.

Figure 8 is a sectional view taken centrally through one of the pumping units comprising another alternative embodiment of an automatic hydraulic checking device in operative position.

In the embodiment shown in Figs. 1 to 6, two pumps are coupled in series, the first pump discharging into the suction of the second one. It is quite clear that the invention is by no means limited to such an embodiment and is applicable in the case of a single-stage pump as well as in the case in which a plurality of pump stages are provided.

As shown in Fig. 1, the pistons l of the first pump are of circular cross-section and are provided at their end adjacent the periphery of the casing 2, wherein they are housed, with a shoulder portion la in order to allow the action or the hydraulic checking means the operation of which will be described hereinafter.

Pistons I, for instance six in number, are uniformly spaced within the casing 2 as also are the pistons 3 of the second pump which are respectively disposed in the same radial planes.

The actuation of the pistons I and 3 is effected by means of eccentrics 4 and 5, the angular shifting of which has theoretically a value equal to Said eccentrics are fitted on a driving shaft 6 or are integral with it, and act upon the cambered heads of the various pistons: through grooved rings 1 constituting the outer race of needle bearings 8.

justment of the shaft 6 is obtained at its free'end,

on one hand, by means of -a thrust bearing I4 with a double row of balls clamped by a screw I5 provided with an outer cylindrical portion and, on the other hand, by means of a second ball thrust bearing I6 fitted on'said screw'cylindrical portion and axially blocked by a threaded plug I! which in turn is screwed and locked, if

need be, in a recess of the flange I2.

To allow the liquid discharged by the first pump to flow into the second one, passages 2a are :provided adjacent the periphery of the casing 2 in each radial plane containing the pistons I and-3.

The pistons I are urged back against the outer periphery of the ring I located round the eccentric-4 by springs i3 abutting against plugs Ifia constituting the head of each cylinder of the first pump and tightly screwed to the casing v2.

The pistons 3 are urged'back towards the ring I located-round the eccentric 5, without the use of springs, by theaction of the liquid discharged by the first pump.

This liquid is directed through check valves II into thechambers 42b, and thereafter discharged through conduits (Fig. 5'), communicating with each other, towards a single collector not shown and connected to the utilization circuit.

The various valves preventing return of the fiuidtowards thesuction-are constituted by check valves such as balls I19 the seats of which are provided for the first .pump in the inner passages Ir of pistons l, andfor the second pump in plugs .20 :closing the cylinders ta in Which reciprocate the pistons .3 and which are to that end tightly secured-to the casing :2. 'When the *various valves are open, the balls is abut against insert members 21 :as shown \in :Fig. 1. Relief valves 22 are disposed, :in a way known perse, at the upper part of cylinders 5 c and communicate with radial-conduits 2d connected with cen tral chamber -74 for allowing return of excess of fiuid towards said central chamber, in the event of :seizingof a piston 33in its outermost'position. The spring422a of each relief valve 22 -is so designed that the ppressureexerted on said valve is greater than the pressure maintaining the corresponding piston 3 against the cam lduring the filling of the corresponding cylinder 3a within which reciprocates said piston 3.

The device operates 'a's follows: i

The liquid to be pumped is admitted to the center, of thecasing 12 within the central or suction chamber M by conduit to contained in a diametral plane comprised between two succes- -sive;-pistons l of the first'pump,=preferably in-the diametral plane passing through the checking device which will be described hereinafter (Fig.

Theoperative cycle of the pump is 'now studied for a-n-assemblycomprising apiston I'of'the first .pump and'the piston3 of thesecond pump which is associated thereto.

position; The stroke of eccentrics 4 and 5 have the same value and the cross-sections of piston 3 and of the outer part of piston i are equal. Both pistons l and 3 being in said positions, the liquid fills the inner passage I f of piston i, the part of cylinder Ic located on the outside of said piston I and the conduit 211. When shaft 6 rotates, the operative cycle is as follows:

" Piston' -I moves towards the periphery of the pump in opposition to the liquid contained in :cylinder 10 and in conduit 2a The clearance existing between the ball I9 of said piston I and the walls of its housing in said piston being small, said ball is applied against its seat thus closing the-communication between the inner passage I j vand the cylinder 'ic.

The liquid contained in cylinder lo and in conduit 2a is put under pressure and pushes back the ball is housed in the plug 21) against the stopping member 2|; the liquid under pressure fills the part of cylinder 3a located'onthe-outside of piston 3, and applies said piston against the ring I while being -dis-- placed towards the shaft. Said liquid cannot escape through -valve II, said valve being maintained inuclosed position-by the pressure-existing in the utilization circuit 'with which it is -connected and "by its own spring, while the ball 22 which-cooperates with piston I actsas safety .device. The relative positions'of pistons I and 13, balls I9, 1! and 22 remain 'unchangedas long .as pistons I and 3 have not respectively attained theiroutermost and innermost positions.

When piston I moves from its outermost position-towards the shaft under the-actionof spring I'B, it generates vacuum in the conduitla. Said vacuum has for effect to displace the ball I9 of piston I towards its-:stopping-member 2'I, on the one hand, EIICL'OI]. the otherhand'to displace the ball I9 of plug 20 against itsseat. Such efiects are 'facilitated'by the fact that liquid contained in the central chamber M is simultaneously'admitted within the inner passageof I jof piston -I, throughzport .Ib, while theiiquid contained in the part of cylinder to. :located on the outside of piston 3 is put under pressure by the outwardly directed movement of said piston 3. Simultaneou'sly, the liquid contained in said partof cylinder ta dischargesthrough'valve 'H into-conduit 20. Then, when "pistons 1 and 3 come back to their :original position, the cycle begins "again, the 'valve ll being :closed hy the action of its spring and by-the .qpressure'existing in thewutilization Icircuit. For'eachrevolution of shaft 5, said cycle is repeated-as many times as-the-pump contains-pairs-of associated :pistons -I and 3.

To the discharge collector formed by the-conduits Qcis connected aconduit I2 (:Figs. 3.and5),

which communicates with recess 2e formed in the 'casing 2, while said collector is :connected to the utilization circuit through a discharge port 3.

The checking device (Figs. 2 to 4) comprises .a double valve having :an intermediate head 23a and two'opposite shanks 23b and 230.

:formed-on their free ends with portions having triangular cross-section :23e and .23 (Fig. 4). The cylindrical portions of said shanks '23b and 23c -move in cylindrical bores of corresponding diameter which are formed in the'casing 2. The double valve head 23a is located ina chamber 23d and acts as stop means for'the'longitudinal 'displacement ofthe double valve-23. Said chamber 2311 communicates with a passage 'Zfl' 'connected with a circular channel 21 formed into the flange l2 and into which open passages 2 which respectively communicate with chambers 2p formed in cylinders |c between the shoulders la of pistons l and the shoulders lg of said cylinders.

The tightness is obtained by the abutment of the double valve head 23a on the lower wall of the chamber 23d and by the accurate penetration of the cylindrical portion of the shank 230 within the corresponding cylindrical bore.

The cylindrical portion of the shank 23b does not penetrate within the corresponding cylindrical bore and the communication between the passages 2g and 2f| is obtained as a result of the play existing between said cylindrical bore and the triangular portion 23c of the shank 23b.

The double valve 23 is resiliently urged against its lower seat by a spring 24 the initial. tension of which is adjustable by means of a threaded plug 25 and of a lock-nut 26 (Figs. 2 and 3).

When the pressure in the discharge collector formed by the conduits 20, that is to say in the utilization circuit, increases and slightly exceeds the pressure exerted by the spring 24, the liquid contained in the conduit 12 communicating with the recess 2e slightly raises the double valve 23 until the cylindrical portion of the shank 23c rises out of the corresponding cylindrical bore.

At that time, the liquid penetrates into the chamber 23d housing the double valve head 23a. The cylindrical portion of the shank 23b closes the corresponding cylindrical bore. The cross-section of the cylindrical bore within which moves the cylindrical portion of the shank 23b being greater than that of the cylindrical bore through which moves the cylindrical portion of the shank 230, the action of the liquid tends to overcome the resistance of the spring 24. Said spring 24 suddenly yields and the sudden movement or snap action of the double valve head 23a urges said head against its upper seat. The liquid suddenly flows from the chamber 23d through the passage 2f| and the circular channel 21 to the passages 21 communicating with the chambers 21) of the cylinders |c between the shoulders la. and lg, whereby all the pistons l are pushed outward towards the plugs |8a; the suction is thus automatically checked and the pump is automatically and instantaneously cut out.

When considering the step where all the pistons are locked, i. e. where the double valve 23 has its valve head 23a urged against its upper seat, if the pressure falls slightly below said predetermined value in the recess 2e, the double valve head 23a is urged back on its lower seat b the spring 24. The cylindrical portion of the shank 23c closes the corresponding cylindrical bore, thus cutting out the communication between the recess 26 and the passage 2f|. Then, the cylindrical portion of the shank 23b rises out of the corresponding cylindrical bore so that the communication between the passage 2f| and the passages 2g via the chamber 23d is established. The displacement of the double valve 23 ends through a sudden movement or snap action, then the pressure acts only on the cylindrical portion of the shank 230 which has a crosssection smaller than that of the cylindrical portion of the shank 23b. The liquid contained in the chambers 210 is discharged towards the supply tank through passages 2f, circular channel 21, passage 2 and conduits 2g communicating with the radial conduits 2d. The pistons I re-.-

turn into engagement with the annular member 6. of the eccentric 4 and the pump resumes operation.

The chief advantages of the improved pump as described consist in rendering unnecessary, on one hand, all conduits, flexible or not, disposed outside ordinary pumps and which require constant maintenance, and, on the other hand, manometric and electrical devices used in the known art to cause cutting out of the pump at a certain maximum pressure, these advantages being obtained whatever the characteristics of the pump employed. i

In the forms of embodiment illustrated in Figs. 7 and 8, the hydraulic checking means employed is of the type of that described in connection with Figs. 1 to 6 and will not be described anew; the same numerals refer to similar elements as in Figs. 1 to 6.

In the form of embodiment illustrated in Fig. '7, each of the radial pistons 50 of the pump, is cylindrical and comprises a cambered head 33 which normally engages a grooved ring 1 constituting the outer race of a needle bearing, 8 the inner race of which is formed by the eccentric 4 keyed on the driving shaft 6. Each of said radial pistons 50 comprises an axial bore 30 communicating by a passage 3| with ports 50b provided near the inner end of the piston 50. These ports 50b communicate with a central chamber 14 provided in the casing 2. The passage 3| is normally closed by a valve member H), such as a ball, when the piston 50 moves outwardly. This ball H) is maintained in its housing by a washer 32 which bears against a shoulder of the axial bore 30 and on which acts a helical spring 5| the other end of which bears against the bottom of the axial recess of a threaded plug 52 constituting the cylinder head corresponding to piston 50. Said spring 5| tends to maintain the piston 50 in engagement with the ring 1.

According to the present invention, the piston 50 is located within the bore of a bushing 35 provided with two diilerent diameters'so as to form a shoulder 36 to allow for the operation of the hydraulic checking means as explained hereinafter. Said bushing 35 is slidably fitted in corresponding bores of the casing 2 and tightness of fit between the body 2 and the bushing may be provided by segments 31 for example.

Said bushing 35 is urged towards the center of the pump by a helical spring 38 bearing, at one end, against the upper face of said bushing 35 and, at the other end, against the threaded plug 52. The centerwards motion of said bushing 35 is limited by a collar 39 provided round the outer end of said bushing and which bears against a shoulder 40 provided in the casing}. In this extreme position an annular chamber 4| is formed below the bushing shoulder 36. This chamber 4| communicates through a passage 2) and an annular chamber 21 with the hydraulic device controlling the cutting out of the pump, which is similar to that, already described. 1

The bushing 35 is connected with the piston 5|) through a transverse member 42 secured to the inner end of said bushing and passing through suitable apertures of the piston 50 which are formed, for example, as shown in Fig. 7 by two of the inlet ports 50b. On this member 42 and co-axially with the piston passage 3| is secured a needle or rod 43 the function of which will be explained hereinafter. In the normal position of th bushing 35, i. e. when its collar 39 bears against the casing shoulder egetogsae 7 E ami the piston 50 is in innermost position as shown in Fig. '7, the needle 43 is not in contact "with :the .ball :19 which then rests uponits seat. Furthermore a icertain play .is .maintained between the member 42 and the upper end of the :ports 50b.

:A :suitable relief valve 3.22 :is located, as i'already described, at the outer portion of each cylinder 50c and a radial passage 2dis provided for the return of excess of liquid into the central suction "chamber 14. The discharge of each cylinder is effected through a passage Za.

fin operation, the rotation of the shaft 6 of the eccentric! keyed on'it causes successive displacements of the different pistons 50 towards the periphery of the-leasing l2, and consequently discharge :of the liquid contained in the various cylinders through passages 2a. The suction is effected "from the center suction chamber '14 through ports 50b and axial passages 3| prov i'ded 'withinthevarious pistons 50, during the return stroke of said pistons under the effect of springs 5 1.

When pressure in the discharge collector, i. e. in the utilization circuit, exceeds a predetermined value, Lit has been seen that the device controlling the automatic cutting out of the pump, called the hydraulic checking means and above described (double valve 23 and its seats), admits liquid under pressure into the passages 2!. This liquid penetrates into the annular chamber "Al and moves the bushing 35 in the direction of the arrow 1. When this displacement'starts,the'needle'43 raises the ball 19 from its seat and the liquid contained in the cylinder may return to the central suction chamber T4. Thereafter, the member 42 is brought to bear on the'outer end of the port 501) and the bushing 35 then draws the piston 50 towards its outermost position or checking position. In this position the control eccentric 4, while revolv'ing, no longer actuates that piston, thus effecting automatic cutting out of the pump.

As-soon as the discharge pressure of the pump returns to normal, the piston-valve 2'3 returns to its normal position in which it causes the passages :21 to communicate with the suction through circular channel 21 and conduits 2f], 29 and-2d (Fig. 2). The bushings'35 are brought back by the springs '38 to their innermost positions; theircollars 39 bear against the casing shoulders 40 and the pistons I return under the action or the springs 5| to their innermost positions into engagement with the ring I mounted on the-eccentric 4; the pump is then once more operative.

Fig. 8 shows another iorm of embodiment of the hydraulicallycontrolled checking device acting on the various radial pistons of the pump. Each of the pistons 55 is cylindrical and slides directly in a suitable radial bore "550 formed in the casing 2. Said piston '55 is driven (as in the case of theembodiments illustrated in Figs. 1 and '7) by a shaft 6 provided with an eccentric 4 and is urged into engagement with said eccentric by a spring 56 hearing, at one end, on athreaded'plugi'l constituting the head of the cylinder end, and, .on the other end, bearing on a threaded ring 45 screwed into a tapered portion of the axial piston bore 58. Saidbore 58 communicates with the central chamber 14 through a passage-59 and a-transverse port 551) 8. 46 bearing against said ball and against the innerface of the threaded ring 45.

--At its periphery, the piston :55 has a :groove 4 which is substantially semi-circular in crosssection and with which may engage the substantially hemispherical end of a small piston '48 when the piston 55 is in outermost position. Said zsmall :piston '48 is tightly mounted in a corresponding bore 249 provided in the casing and the axis of which is perpendicular to the cylinder axis. :Into said bore 49 opens the :passage 2*) connected to the hydraulic checking device.

in "operation, when the discharge pressure of the :pump exceeds a predetermined value, the hydraulic checking device, as above described in connection with Figs. .1 to 16, becomes operative :and admits fluid under pressure into the various passages 21 each of which corresponds to one-20f :the cylinders. The liquids urges back the small pistons 48 against the pistons 5.5 and, as soon as the latter insuccession attain their outermost position under the :action of the cocentriomltheispherical end of the corresponding small piston 48 engages the corresponding periph'eral'groove ll'l of each of those pistons. The latter are thus maintained in this position cor-- responding to the cutout condition of the pump so long as pressure .is applied on said small pistons.

As soon as the discharge pressure ofithe pump returns to normal, thepiston valve 23 returns to its normal Ep'osition, Passages '2 are then .put in communication with the suction through channelZ'l and conduits 2f], 2g and 2d (Fig. 2). At that instant the small pistons48- areno longer forced againstthe'piston 55 bytheliquidpressure and they are pushed back into their recesses by meansofthe pistons 55 themselves acting on'their spherical ends, 'whilesaid pistons 55 are brought back into engagement with the eccentric under the action of the-springs 56; the 'pump is therei ore once more operative.

In the various :forms of embodiment above 1 described and illustrated, it will be seen that by simply removing the threaded plugs l8a, 52 or 5 1, the corresponding pistons I, '50 and 55 may eas'ilybe removed, and in the form of embodiment' illustrated in'FigI'T, thebushing 35, wherein the pistens'slidepmay also be removed.

suc h dispo's'ition provides for the possibility of ready dism-antling of the pump and replacement dfthe bushings 35 and of pistons tilL'wearchiefly occurring'between't'he bushings and the pistons in "the case of embodiment illustrated in Fig. -7.

l. In-a -r-adial-pi-ston pump for liquids, a casing having an inletchamben'an outlet port and uniformly spaced-radial cylinders the inner ends of'which are i-n-communication with said chamber, means for closing the outer ends of said cylinders, atubular piston in each of said cylindersandremovable-through the outer end thereofgsaijdpistonshavingblosed inner ends projectinginto said chamber and inlet'ports to connect the same with said chamber, a central shaft journalled in said casing and rotatable within saidchamber, 'an'eccentric on said shaft having driving contact with said closed inner ends of said pistons, "check valves located within said respective pistons-to prevent return of the liquid through the same toward said chamber, discharge 'ducts connecting the outer ends of said cylinders with 'said outlet 'port, resilient means 'ior urg'ing isaid pistons against said eccentric,

hydraulic means for immobilizing said pistons in their outermost positions corresponding to the end of the compression stroke when the delivery pressure of the pump exceeds a predetermined value, whereby said pump is thereupon automatically and instantaneously put out of action even though said shaft continues to be actuated vby a continuous rotational movement at a suitable angular velocity, and hydraulic means for actuating said immobilizing means, said hydraulic means comprising a set of interconnected confromly spaced radial cylinders the inner ends of which are in communication with said chamber,

a set of three aligned chambers whereof the first and the third chambers are respectively in communication with said inlet chamber and said outlet port, and two aligned channels respectively connecting said first and third chambers with the second chamber of said set, the diameter of the channel interconnecting the first and second chambers being slightly greater than that of the other channel, means for closing the outer ends of said cylinders, a tubular piston in each of said cylinders and removable through the outer end, thereof, said pistons having closed inner ends projecting into said inlet chamber and inlet ports to connect the same with said chamber, a cen tral shaft journalled in said casing and rotatable within said inlet chamber, an eccentric on said shaft having driving contact with said closed inner ends of said pistons, check valves located within said respective pistons to prevent return of the liquid through the same toward said inlet chamber, discharge ducts connecting the outer ends of said cylinders with, said outlet port, re-

silient means for urging said pistons against said eccentric, hydraulic means for immobilizing said pistons in their outermost positions corresponding to the end of the compression stroke when the delivery pressure of the pump exceeds a predetermined value, whereby said pump is thereupon automatically and instantaneously put out of action even though said shaft continues to be actuated by a continuous rotational movement at a suitable angular velocity, a doublevalve located in said second chamber and having two aligned opposite shanks ended by triangular sections and which are reciprocally guided by said channels, resilient adjustable means for normally maintaining said double-valve in the position for which the communication between said second and third chambers is closed, a set of interconnected conduits respectively connected with said immobilizing means, and a passage connecting said second chamber with said set of interconnected conduits, so that, when the delivery pressure of the pump exceeds said predetermined value, the double-valve suddenly closes the communication between the first and second chambers and opens the communication between the third chamber and the set of interconnected conduits via the second chamber and the passage, whereby said immobilizing means are operative, while, when said delivery pressure falls slightly below said predetermined value, said resilient adjustablemeans suddenly returns said double-valve to its normal position.

3. A radial-piston pump for liquids, according to claim 2, wherein each piston is formed with a shoulder in the upper part thereof, said shoulder being associated with a flange formed on the inner surface of the corresponding cylinder for providing a hydraulic chamber between said flange and said shoulder, the corresponding conduit of the set of interconnected conduits opening in said chamber, whereby the latter acts as immobilizing means.

on the inner part of said bushings crossing the inlet ports for connecting said pistons with said bushings when the latter are operative, and means fitted on said rods for opening the check valves at the beginning of the outward displacement of said bushings.

5. A radial-piston pump for liquids, according to claim 2, wherein the casing is formed, for each cylinder, with a cylindrical recess perpendicular to and opening within said cylinder, the corresponding conduit of the set of interconnected conduits opening in said recess, and wherein the immobilizing meanscomprises small pistons'reciprocable in said recesses under the action of the pressure existing in said set of conduits and the heads of which are adapted to penetrate in suitable grooves formed on the pistons when said pressure exceeds the predetermined value, and means for allowing the disengagement of said small pistons from said grooves when said presin parallel planes, the inner ends of said cylinders being in communication with said inlet chamber, a set of three aligned chambers whereof the first and the third chambers are respectively in communication with said inlet chamber and said outlet port, and two aligned channels respectively connecting said first and third chambers with the second chamber of said set, the diameter of the channel interconnecting the first and'second chambers being slightly greater than that of the other channel, means for closing the outer ends of said cylinders, two sets of pistons respectively in the cylinders of said two sets of cylinders and removable through the outer ends thereof, said pistons having closed inner ends projecting into said inlet chamber, the pistons of the first set being tubular and having inlet ports to connect the same with said inlet chamber, a central shaft journalled in said casing and rotatable within said inlet chamber, two eccentrics on said shaft having an angular shifting substantially equal to and respective driving contact with said closed inner ends of the pistons of said two sets, check valves located within the respective pistons of the first set to prevent return of the liquid through the same 11 toward said inlet chamber, connecting ducts for connecting two by two the outer ends of the cylinders of said two sets of cylinders, resilient means for urging: the pistons" of the first set against the" corresponding eccentric, check valves located at the junction of the connecting duets with: the cylinders of the second set to prevent return: of the liquid through thesame toward the cylinders of the first set, discharge ducts conmeeting" the outerends of: the cylinders of said second set with said outlet port, check valves inserted in said discharge ducts, hydraulic means for immobilizing the pistons of the first set in their outermost positions corresponding to the end of the compression stroke when the: delivery pressure of the pump exceeds a predetermined value, whereby said" pump is thereupon' automatically and instantaneously put out of action even though said shaft continues to be actuated by a continuous: rotational movement at a suitable angular velocity, means for preventing an excess or pressure the cylinders of the'first set in the: event one at least of the pistons of the second setbe seized within the corresponding cylinder, at double-valve located in said second chamber and having two aligned opposite shanks ended. by triangular sections and which are' reciprocally guided by said channels, resilient adjustable means for normally maintaining said double-valve in the position for whichthe communication between said second and third chambers is closed, a set ofinterconnected conduits respectively connected with said immobilizing means, and a passage connecting" said second chamber'withsaid set of interconnected conduits, sothat, when: the delivery pressure of the pump exceeds said predetermined value, the doublevalve suddenlyclosesthe communication between the first and second. chambers and opens the communication between the third chamber and the: set of interconnected conduits' via the second chamber and the passage; whereby said immobilizing means are operative; while-, when said delivery pressure fallsslightly below saidpredetermined value, said: resilient adjustable means suddenly returns: said doublewalve inits normal position.

'7 A two sta'ge" radial piston pump for liquids, according toclaim 6; wherein each piston of the first set i's-formed with a shoulder in the upper part thereof, saidshoul'der being associated with a; flange formed on' the inner surface of the corresponding cylinder for providing a hydraulic chamberbetween said: flange and said shoulder, the corresponding conduit of the set ofinterconnected conduits opening in said chamber, whereby the latter acts as immobilizing. means.

8. A two-stage radial piston pump for liquids, according to claim 6; wherein the immobilizing means comprises reciprocable bushings surrounding the: pistons of the first? set; located. in the cylinders of the first set and formed with circular grooves and with shoulders; said shoulders being associated With flanges formed on the inner surfa'c'es of said cylinders for providing hydraulic chambers between said shouldersandsaid flanges, the conduits of the set of interconnected conduits respectively opening in said chambers, said bushings: further having seal rings located in said grooves, rods fixed on the inner part of said bushings crossing the inlet ports for connecting. said pistons of the first set wit-h said bushings when thelatter are operative, and means fitted on said rods for opening the check valves corresponding to said pistons of the first set at the beginning. of the outward: displacement of said bushings.

9a A two-stage radial piston pump for liquids, according to claim 6, wherein the casing is formed, for each cylinder of the first: set, with a cylindrical recess perpendicular to and opening within said cylinder, the corresponding conduit of the set of interconnected conduits opening in said recess, and wherein the immobilizing means comprises small pistons reciprocable in said recessesunder the action of the pressure ex isting. in said set ofconduits and the heads of which are adapted to penetrate in suitable grooves formed on the pistons of the first set when said pressure exceeds the predetermined value, and means for allowing the disengagement of said small pistons from said grooves when said pressure falls slightly below said: predetermined value.

10. A two-stage radial piston pump for liquids, according to claim 6, wherein the means for. preventing an excess of pressure comprises relief valves respectively connected with the outer end of the cylinders of the first set, said valves having springs adapted to exert thereon a pressure greater than the normal delivery pressure: of the pistons located in said cylinders, and ducts for respectively connecting said relief valves with the inlet chamber.

GEORGES PAUGET.

References Cited in the file of this patent- UNI'IED STATES PA'IENTS Number Name Date 831,890 Plane Sept. 25-, 1906 1,409,786 Sansbury Mar. 14, 1922 1,461,456 Reynolds July 10, 1923 1,979,863 Carruthers 1 Nov. 6, 1934 1,989,117 Svensonn -1 Jan. 29, 1935 2,374,867 Knapp 1 May 1, 1945 FOREIGN PATENTS Number Country Date 237, 57 Germany 1911

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