US1685760A - Hydraulic drive for broaching machines and the like - Google Patents

Description

HYDRAULIC DRIVE FOR BROACHING MACHINES AND THE LIME Filed March 26, 1924 n n.r vv'nsfr, or naar nonnen, confusesteur, 'sesiones vro 'ann a. n. aaron i nanna-tirare nur ron encuentras Macnruns ann man man application and snaren es, met. .serai nu. reacts,

'lhis invention relates to improvements in s `hydraulic drive tor breaching machines and the like. ll/lore particularly it relates to machine tools vvherein there is a, reciprocating member; Whose stroke in one direction is a Working stroke executed under high pres- 4 sure and necessarily at'relativel4 slovv speed,

lout it is `most convenient tohave a pumpV which can ordinarily he driven alvvays in one direction and. at constant speed. 'lhe invention may he applied vtith such aapump, as Well as vvith .variable speed and variable output-pumps. The reciprocating member is ordinarily a piston driven to and tro in a cylinder. Assuming that the driving pump, when operating at lull speed, can

deliver a certain maximum volume ot oil v heavier constructiem required to resist the'l llli stresses, and because olv the conpresshility and increased elastic etlect ot the oil which is ordinarily used as the Working medium.

Another alternative vvould he toemploy a pump ot' considerably greater capacity, and to run it at reduced output on the Working stroke; hut this is costly tor vsise ol pump and tor cost ot applying it to a machineI otl this kind9 as vvell as less eiiicient. llt is an ohject ot the invention to provide lor ohhlt taining a return stroke ot much greater speed' than the Vvvorlring stroke vvithout the chicctionahle incidents ahove mentioned, and to do this vvith an arrangement Which is eco`-' nomicalot'space as vvell as simple in construction.VV

'lhese ole-jects are attained ley arranging a com-hination et cylinders, one ot" suitahly other of suitably small size But vvith the large size t'or the vvorln'ngr stroke andanbor a quick return stroke, the latter, in the preferred term, belng` housed Within the former. To this end, the piston rod, which transmits povver :trom the Working piston, to the reciprocat-in element., as tor example to the dravv ro and tool ina loroaching machine, is made tuhular and hollow to near the :toolgand its hollovv is extended through -the Working' piston. rllhus'it 'becomes an open-ended small cylinder. moving to and tro vvth the piston and tool-head; and a aedtuloe is inserted into this hollovv trom the head or drive'end oi thefmachine so as to telescope into it with a smooth running lit, vvhenthe Working piston moves to and tro. The end ot'/ this piston rod which vis tovvard the toolis ot' course closed. Piping connections are provided by which the pump on the. Working stroke delivers oil into the large cylinder against the Working piston, and on the return stroke delivers oil into the smaller ylinder, against the tool head end ot the sm ll cylinder. its the Working cylinder it much the larger, in

-volume to he lled per tootfot' travel, the

delivery et any -certain volume trom; ythe pump vvill move the piston and tool consideraloly farther in a given time 1t it @he put into the small cylinder thanI it put into the large cylinder. WTherefore, it the ttt llt

ttl

pump discharge he directed into each in turn,

at its hired normal or maximum capacity, it vvill return the tool head much more rapidly the n it draws it on the Working stroke.

."lothis endv the pump is in ett'ecntconlln pounded 'with the Working piston vvhich it drives. to displace oil in the `Working cylinder at arate much greater than the pump alonewould displace it; lout all oil the Work stroke is through the pump alone.

lin each-case reliet is provided 'lor the tlovv ot oil, vother thanl -that which goesA through thev pump so as to make the parts all tree movitlg. 'ln particular., such a conn ttl litt) duit is arranged leading trom the high pressure side et the vvorking piston toits pressure-tree side, ller vthe return stroke. ller preparation lor the Working stroke suit# ahle valve may close this passage simultanef ously vvith the reversal et pump or pump connections; and the same valve may simultaneously open another passageter the'tlotv et oil treely out' trein the said pressuredree side ot the Working pist/on tothe pump, to he llltl delivered. thereby under high pressure directly into the working cylinder on the high pressure side of the piston. An elevated reservoir for oil open to atmosphere, connects with the main cylinder on its pressurefree side, and on its pressure side at strokeends if desired, to receive and' to supply the differential of oil for keeping the system filled at all positions of the Vmain piston, and to free the oil itself from air which gets into it. All of this part is automatic, and results from the application of the pump discharge against the working piston on the working stroke and against the tool head (in effect) i on the return stroke.-

The .invention may be embodied in various arrangements of parts, passages and connec-A tions lfor attaining the same general result, that which has been described above being a preferred form. Its application is not limited to horizontal cylinders, nor to broaching machines, but it is applicable generally to hydraulic systems for propelling a reciproeating element powerfully and slowly in one l direction, as on a working stroke, and rap- Figure 1, the slide valve; but this is shownl in the closed position which occurs between strokes.

The drawing indicates thev frame 10 of a horizontal broaching machine of the pull broach type wherein a tool holding head 12 is moved to and fro by a draw rod 14. The latter is moved on its workin stroke by the piston 18 fast on its end within the main 'cylinder"16. ".[n the preferred form of the invention this draw rod is tubular having one end open through the piston,but having its end which is toward the toolhead 12 closed.'

Any suitable liquid, customarily oil, is propelled by a pump 20 of any suitable type in such manner that the oil is alternately forced into the expansible chamber 19 on the near side of the piston between the draw rod 14- and the walls of cylinder 16v (which space will be herein forconvenience called the work chamber) thus driving the piston 18 on the working stroke, and into the expansible chamber 21 within the draw rod (herein referred to as the .return chamber); the oil being in each case simultaneously withdrawn from the other chamber, This involves a rever-sal of flow of the liquid, which may be effected either 4by a reversal of the direction of discharge of the pump or b other suitable means. The ump 2O is indicated diagrammatically as eing alvariable displacement piston pump continuously rotating in the same direction, in which the pistons are eccentric, flow ceasing when they are set into concentric relation, where they have a stroke of zero length, and beginning in the opposite direction when they are set past the center into eccentricity on the other side. Such pumps driven by electric motors are well known and therefore the details are not illustrated.

In the preferred form of the invention the idle chamber 23 on the remote side of the piston 18 is filled with oil with constantly open connection to an elevated open reservoir 24 of oil; except that a stationary pipe 22 extends axially through the remote head of the main cylinder 16 so as to telescope within the draw rod 14 with an easy running lit. This should fit tightly enough, aided by packing if needed, so that there is little or no escape of oil past it from the interior of the draw rod. rlhis fixed tube 22 delivers into the return chamber 21 beingconnected by a pipe 26 with the low'pressure discharge pipe 25 of the pump 20. The relief valve 27 provided for 'this part of the system may be set so as to open at a low pressure, slightly exceeding that which is required to drive the rod and tool head idly back on their return stroke. For example, in one machine enibodying the invention wherein the chamber 21 within the draw rod has a diameter of two and one-eighth inches a setting of this relief lvalve to open at 200 pounds was found suitable to give protection in case unusual rcsistance should be encountered. This relief Valve may conveniently discharge into a reservoir 30 shown in the drawing as underlying the apparatus and receiving also a drain 29 from the pump for any oil that may leak out therefrom, and one from the relief valve 37 of the high pressure pipe 36 leading from the pump 2O to the work chamber 19. The relief valve 37 for this part of the system must be set to operate at a very high pressure, in a machine'of the character described, for example at 2000 pounds per square inch, because of the high resistance encountered by the tool which is drawn on its working stroke by the piston 18 when oil is forced into the vworking chamber 19. A pipe 46 provides a b-y-pass around the piston between the ends of the main cylinder 16, that is, between the work chamber 19 and the idle chamber 23, and is provided with a valve, which may conveniently be a slide valve 47 operated by rod 48, for opening and closing such by-pass. This valve 47 may also control a connection between the low pressure discharge 25 from the pump and the idle chamber 23 of the main cylinder, by controlling an loo lll

p neueren inlet trom the pipe 26 tothe seid loy-pess ld in such menner thet when the pump is set to propel oil outvverd through the lovv pressure pipe its discherge enters only the pipe '26., end' through it the return chemloer 2l; hut when the pump is set to lill the Work chemher' t9 this vulve di is set so thet oil comes to the pump hoth trom pipes 26 end t@ end thus comes trom hoth the return chemher 2l end the idle chemher 23. @uch shilts ere edected in pumps ont this cherecter hy e. movement ot one or the other elements in the ump; end in the present cese this is eccomp ished hy the control rod 50 vvhich is ectueted either hy hund es through the lever 52, or eutometieelly es hy the engegement ot e lug 5t on the tool heed with e lug 53 essocieted with the hund lever 52 end rod 5U, to stop the motion in the returning direction, or hy its engegement with e similer lug 55 to stop its vvorlring strolre. These errengements muy he veried es desired eceording to 'eny lrynown or suitehle style, lout it is convenient lor the purpose oit the invention thet the pump control rod titl, however ectueted, he connected elso to the vulve rod it so thet s'imulteneously vvith the shitting oit the pump there is e shitting oit the velve il', "l'lhe slide vulve t7 should he so connected thet vvhenthe `pump comes to nero output the-connection trom pipe le to the vrorlr chemher l@ hecomes closed; end so thet vvhen the output oil the pump hegins endirr creuses in the opposite direction thet ert oit the vulve which closes the connection rom ld to 2li opens simulteneously with the heginning und increese oit pumping in seid opposite direction. 'Under these cireumstences the invention permits the electric motor or other drive ot the pump to run elvruys et lull 'lill till tllli speed, end permits the delivery oli the pump to he elvveys et its meeimum eepecity, except uhile heilig shitted :trom one direction to the other or vvhile stopped, The pump muy thereitore he designed Atu here such out ut es is-necessery in order to produce the desired meriummspeed voit" the rrorlriug strolre, thet is, lor eirpe-nding the rrorlr chemher lil et e pressure' sey ot' 2300 pounds. A gege i9.`

mey he provided lor showing pressure conditions Within the rvorlt chemher, hy `which the resistence oli the vvorlr to the strolre muy he ohserved, enehling the operetor to 'reduce the rete oli the pump it lthe leed is extremea or to tell hovv much he een increese its pete on lighter vrorlr, il the pump leeppens to' he opereting et less then meirimum output. lliceording to the neture oli' the rvorlr which is to lie done the reguler speed 'lor e perticuler joh muy he lined either et the menirnum cepecity ot the pump or something less iii it he desired to operete through the vvorlr more slorvly, which lest might he either ifo-r the sehe ol the Worlr or lor getting greeter presure trom e given motorot smell sine.

I"llhe operetion ol the epperetus thus de.-

idle chember 23 end' forces it into vvorlr chem her l9. Then oil thus crovvdedout oil idle chemher 23 hy the edvencin piston i3 is more then cen hereceived in t e vvorlr chemher lll, loeceuse the rod ll is larger then the tuhe 22 which telescopes within it; und enough oil to compensete tor this is crowded up intot-he reservoir 2li. When the strolre is ended the shitting ot rod t8, either eutometicelly or hy hund, simulteneousl vvith the shitting oli' the pump, stops ell motion. When the return strolre is to hegiu the further shitting ol rod t8 ceuses oil to he teken 'trom the Worh chemher i9 lend to he forced hy the pump through the pipe 26 into the return. chemher 21, lling thet cheminer ver'y rapidly becuuse it is so Smell, end thus returning the tool heed, drevv rod end piston 18 to position lor enother vvorlring strolre very quickly, es compered with the time teken tor driving them on the vvorlring stroke, While the excess ol oil torced trom the Worl: chemher l9 hy the edvencing piston l@ flows through the hy-pessege l@ into the idle chemher 23:; end some oil is dreven into the idle chemher 23 trom the reservoir 2li, to compensete tor the/ thichness ot the vvells ol the drenT rod 2l.

lt is not necessery thet the idle chemher 23 litt sev

litt

contein oil. But it is edventegeous to heve oil in the chemher 23 heceuse it reduces the lilrelihood ol eir etting pest the piston ld into the vvorhing ody ol oil end rendering it more elestic, end loeceuse it melres it less importent to heve e tight pecking hetvveen introduce eny. prohlem el' disposel ot the leelrege...

llt is desirehle thet the hody ot oil should he tree trom eir, the presence ot which introlllti i lltl duces en element oil compressihility end resilience into the tluid medium which in turn reduces the positiveness et' operetion ot the tool end introduces irregulerities. The invention provides ineens, lor meinteining the oil tree end cleer ot eir, which 'ere veluelole in ceses vvhereelesticity ot the lluid medium is ohjectionehle, hy errenging reservoir 2t et the highest pert ot the system end having e connection thereto trom the to level oi the idle chemher 23, so thet eny eir huhloles which get intov the system und ere cerried hy the oil to this pert oil it muy rise to its top end thence rise to the reservoir 2t end escepe. lli similer cleerernreV lor escupe o'l eir is provided on the Worlr chemher end hy roviding e connection trom the evorlrI chem er to the reseri ieu by pressure within the work chamber or by flow of oil out from the work chamber into the reservoir and having a weak spring which opens the valve in the absence of controlling circumstances. The spring should be weak enough so that this valve will be thus closed even during the return stroke by the slight pressure or outflow of oil; but it will be opened by the spring at the end of stroke in either direction andremain open while there continues to be neit-her pressure nor iow. This periodic opening of the workA chamber beneath a body of oil permits the rising and escape of any air that may be within and. insures its being filled with oil at the beginning of each working stroke;

2Fhe casing and valves in the circulating system may be of anyAsuit-able kind and are not necessarily operated by a single unit as illustrated in the valve 47. rlhe arrangement shown is, however, especially advantageous for a machine of the character mentioned. ln this the barrel of the valve 47 has a longitudinally movable plug bored from the end and from the top. Oil from the work chamber may enter its top when it is properly positioned to open the by-pass; and may at all times pass by this plug, between work chamber and pump, by passing through a chamber 47 in the wall of thevalve which surrounds this plug. f

A circulating pump 6.0 may be employed to carry oil constantly or at intervals up from the drain pan 30 to the reservoir 24; with an overflow pipe 61 from the latter into the pan 30. A

The reservoir 24 is not necessarily elevated to above the cylinder nor thepan 30 set below the relief valves and pump. These may be otherwise arranged.

The return chamber is not necessarily housed within-the main cylinder 16 and draw rod 14, although this is most convenient, but the arrangement of the return c linder on the axis of the work cylinder as ilustrated has many advantages.

It will be understood that while theforegoing explanation has been made upon the assumption that the reversal of flow is occasioned by the reversal of direction of output of the pump, the invention is not limited to that particular'embodimentof means for reversing the connections lof intake and discharge of the pum :while the pump itself operates continuous y in one direction at its predetermined full speed; provision being made for idling of the ilow while both 'said connections are closed.

Other variations may be made. The invention has been herein described with reference to a horizontal pull broaching machine.v In

the tool at suitable speed on the working stroke and returning the tool quickly for the next stroke, the requirements of the two strokes being mechanically contradictory and the mechanism which is adapted for one has hitherto been unsuitable for the bestideals of the other, even when hydraulic drive has been used. The present invention, by its housing of the small return cylinder on the inside of the draw rod, thus by simple mechanism compounding the pump action for the return stroke and providing for its free circulation through the by-passage, with constant elimination of air, provides a drive which renders the action of a breach positive and steady despite variations in the resistance of the work, reduces the momentum of moving parts, and applies to each part of the stroke the type of power it needs. @bviously the invention can be applied with advantage to other types of broaching' machines and to machines other than broachingl machines so that it will be understood that the iragn'lcnts of machine frame which are shown in the diagrammatic drawing may serve to rcp resent the frame of any machine to which t 1e apparatus is applied.

I claim as my invention:

l. A hydraulic drive t'or a reciprocating element, having in combination, a. pump, having a predetermined output; a cylinder with piston, constituting an expansible chamber; a rod extending through the chamber, rigidly connecting the piston to the said reciproeating element and arranged to pull said element on the working stroke; and a cylinder of smaller cross section than the net cross section of the said chamber through which said rod extends, said smaller cylinder being arranged to effect the return stroke, whereby for the same predetermined pump output the return is more rapid.

2. The combination, in a hydraulic drive for a reciprocating element, of a pump having a predetermined output and an expansible chamber for effecting a working stroke of the element, with an expansible chamber of smaller cross section for effecting its return stroke, whereby for the same predetermined pump output the return is more rapid; the return chamber being housed within the work chamber.

3. The combination, in a hydraulic drive for a reciprocating element, of a pump having a predetermined output; a cylinder; with piston and rod attached to the reciprocating element for effecting a working stroke ci the element; said rod being tubular and opening through the piston; and a stationary space connection for the opening of said reciprocating rod whereby said tubular rod with said space constitutes another and smaller chamber, expansible for effecting the return stroke more rapidly with equal pump output.

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tenured element; said rod being tubular and opening through the piston; and a stationary space connection for the interior of said rod Whereby said tubular rod vvith said space constitutes another and smaller chamber, expansible tor edecting the return stroke more rapidly with equal pump output; the said space connection being a tube telescoping within the piston rod and connectedvvith the pump..

5., 'lFhe combination, in a hydraulic drive tor a reciprocating element, ot a circuit for the reciprocation ot the liquid driving medi um, comprising a pump; an expansible chamA ber in the circuit, terminating said circuit on one side cit the pump, having a moving end Wall tor edecting .a Working stroke ot' the element; an eapansible chamber in and ter minating the circuit on the other side ot the pump, being oit smaller cross section and having a moving end vvall tor edecting a return strolre ot the element; a container having capacity tor a part ot the medium at atmospheric pressure; connections in said circuit vvhereby the pump alternately can shit-'t liquid trom each chamber to the other chamber; a connectionbetvveen the said moving `vvalls oit the respective chambers whereby, during lcupansion ot the smaller chamber on the return strolre, its moving Wall moves to an equal distance the end Wall ot the larger chamber and thereby displaces liquid contents olf the larger chamber at a, rate euceeding the simultaneously occurring shitting et liquid trom the larger chamber to the smaller chamber by the pump; a connection :trom the larger chamber to the said con-` tainer, open during the shitting trom the larger chamber and passing into the container the -said eucess liquid displaced; a connection trom said container to the circuit on the same side oit the pump on vvhich the smaller cham ber is connected, open on the vvorhing stroke;

i and a valve vvhereby thesaid connections or container to vvorlring chamber and to pump are made alternately., f

n, 'llhe combination, in a hydraulic drive tor a reciprocating element, ot a pump, anda cylinder, piston and piston rod, arranged and coccted to the pump tored'ecting the vvorlr titl' tor a reciprocating element, ot a pump; a pair of expansible chambers, one of these chambers being larger than the other oi' them and comprising a cylinder and piston With piston rod providing a pull through the rod i'or moving said element on its Working stroke, andthe smaller of these chambers having its moving Wall located at a distance trom the said piston toward the said element and operating to ed'ect the vreturn stroke of said element; a chamber tor idle liquid; and connections whereby theV pump is supplied trom the return chamber and the idle chamber and delivers to the vvorlr chamber on the Work stroke vvhile on the return stroke liquid passes through pump to the return chamber, and by-passes the pump from the Work chamber to the idle chamber,

8. lhccombination, in a hydraulic drive tor a reciprocating element, oi' a cylinder with piston and rod connected to said element; a luy-passage trom one end of the cylinder to the other having a valve which can be yset to open or close the by-passage; a pump; another passage, from said end of the cylinder through 'the pump and having a to'rlr after passing through the pump, one branch oit which has a-,valve and leads to the said other end oi' the cylinder; and a second cylinder, tor returning the reciprocating elen ment; the second oit said branches leading to the said second cylinder..

9.. The combination, in a hydraulic drive tor a reciprocating element, ot a main cyl inder vvith piston and piston rod attached to the element, the space on one side ot said piston comprising a vvorlr chamber and on the 'lil lill

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other side an idle chamber; a return chaminder vvith piston andA piston rod attached to the element, the space on one side oit .said piston comprising a vvorlr chamber and on the other side an idle chamber; a return chamber Within the piston rod; a pump, means to reverse the direction ot its output, .and liquid iforced thereby alternately into the vvork chamber and the return chamber; and means associated with the idle chamber tor conserving the liquid which is iorced out ot the vvorlr chamber by the piston during the llfi return stroke ot the element and tor supplying it to thepump tobe forced into the vvorlring chamber on the Working stroke.

' ll. 'llhe combination, in a h draulic drive tor a reciprocating element, oriy a main cylinder with piston and piston rod attached to the element, the space on one side of said piston comprising a work chamber and on the other side an idle chamber; a return chamber Within the piston rod; a pump connected by conduits with said chambers; means to reverse the direction of output of the pump, and of liquid forced thereby alternately into the Work chamber and the return chamber; a reservoir open to atmosphere associated with the idle chamber for. conserving the liquid which is forced out ofthe idle chamber by the piston during the working stroke of the element, and which is in excess of the capacity of the Work chamber to receive, and for supplying it to the pump as a part of the liquid to be forced into the Working chamber on the Working stroke of the element.

l2. Hydraulic driving means for a reciprocating element comprising avmain cylinder with piston and rod connection to said element, the cylinder being at one end a work chamber and at the other an idle chamber; a by-passage from one end of the -cylinder to the other having a valve Which can be set to open or close the by-passage; a return chamber arranged Within the piston rod, opening through the piston; a compensating reservoir connected with the idle chamber;

a pump; connections betweenthe chambers and the pump; and a Working liquid moved by the pump through said connections.

13. A hydraulic drive for a reciprocating element comprising the combination of a Work cylinder 4and piston; connections Whereby the expansion stroke of the piston in thev cylinder is a pulling stroke; a smaller other cylinder for the return stroke, connected to receive on the return stroke liquid displaced from the Work cylinder on the same stroke; a liquid pump; an idle chamber to receive liquid forced from the Work chamber-Von the return stroke; and connections to supply said liquid from both the said smaller chamber and the'idle chamber to thepump and thence to the Work cylinder on the Work stroke; said idle chamber being in the main cylinder on the side of the piston remote from the Work chamber.

14. A hydraulic drive for a reciprocating 'element comprising a cylinder with piston,

mentioned cylinder to the other; and a positively controlled valve in the by-pass arranged to be shut for the working stroke and opened for the return stroke. f

.15. The combination, with a hydraulic drive system for a reciprocating element, of a large expansible chamber open to receive flow from one direction for a slow- Work stroke; a small expansible chamber open to receive liow from the other direction for a rapid return stroke; a pump, means to reverse direction of its output and liquid forced thereby for effecting the strokes alternately; a high pressure relief valve in the connections between pump and working chamber; a, low pressure relief valve in the connections between pump and return chamber; a pan and drains thereto from the relief valves; an idle chamber receivingr discharge from the large expansible chamber, and a compensating reservoir connected thereto; and means for interflow of the contents of the drain pan and the reservoir.

16. The combination, With a hydraulic drive system for a reciprocating element, of a Working chamber for a work stroke; another chnnber for return stroke; a pump, means ta reverse the direction of its output, connections from said pump to said chambers, and liquid forced thereby for effecting the strokes alternately; relief valves in the connections to the said chambers; a pan for drain from said relief valves; an idle chamber receiving discharge from the large expansible chamber and a compensating reservoir connected thereto; and a circulating system having a pump delivering liquid from the pan to the reservoir, and an overflow passage from the reservoir to the pan.

17. The combination, in a hydraulic drive for a reciprocating element, of a main cylinder with piston and piston rod attached to the element, the space on one side of said piston comprising a work chamber and on the other side an idle chamber; a return chamber Within the piston rod; a pump, means to reverse the direction of its output, and liquid forced thereby alternately into the Work chamber and the return chamber; and an elevated reservoir and connection to it from the top of said idle chamber for air relief therefrom.

' 18. The combination, in a hydraulic drive for a reciprocating element, of a main cylinder with piston and piston rod attached to the element, the space on one side of said and liquid forced thereby alternately into.

piston comprising a Work chamber and on the Work chamber and the return chamber;

and an elevated reservoir having connection with the top of said Work chamber through a valve, with weak spring, for air relief from said Work chamber.

19. The combination, in a hydraulic drive for a reciprocating element, of an expansible' chamber for effecting its working stroke, with an eXpansible chamber `of smaller cross sectionv for effecting its return stroke, whereby, for equal liquidpdisplacement by the source lll pesare .m

ot power the' returns* is more rapid; the return stroke chamber being housed within the worlr chamber.

20. A hydraulic driveior a reciprocating element comprising the combination oli an annular expansible working chamber; a return chamber co-aXially arranged within the working chamber; liquid pressure means having connections with both chambers; and means controlling the application of the liquid pressure tothe said chambers selectively.

21. A hydraulic drive for a reciprocating machine element especially adapted for broaching machines comprising two pressure cylinders of diderent diameters, the larger of them being set for the working stroke and the smaller of them for rapid return stroke; a reliet space, open to atmosphere, comprising the space on the side other than the pressure side of the piston of the large cylinder; a pressure pump continuously connected with thevpressure chambers of the two cylinders by conduits acting alternately under suction or pressure in accordance with direction of the pump output; a pressure medium, and a valve controlling the flow through said conduits ot said medium; means for reversing the direction of medium flowing from the pump; said conduits and valve being arranged so that the valve during the pressure stroke in the small cylinder connects the relief space with the pressurespace of the largo cylinder, and during the pressure stroke in the large cylinder connects the relief space with the suction Side otthe ump.

hydraulic drive for a reciprocating duits and valve providing the cylinders 'al-v ternately with pressure medium; and said conduits being so arranged that on the Working stroke the pump draws from the small cylinder and the relief chamber, and dischar es into the large cylinder; but on the rapi .return stroke some of the pressure medium can pass directly from the large cylinder to the relieil chamber without having to pass through the pump while other otm it passes trom the large cylinder through the pumps of the small cylinder; and an open reservoir having a connection at the highest point of the oil enclosure in the pressure chamber of the lar e cylinder, and a non-return valve closing y movement in outward direction from the pressure chamber when 'the oil therein is under pressure, and self Opening when the oil therein is not under pressure, providing for automatic air relief.

Signed at New London, Connecticut, this twentieth day ot March, 1924.

DUNALD H.. WEST..

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