US2976878A

US2976878A - Hydraulic control means

Info

Publication number: US2976878A
Authority: US
Inventors: Smilges Robert
Original assignee: American Brake Shoe Co
Current assignee: American Brake Shoe Co
Priority date: 1956-01-16
Filing date: 1957-04-15
Publication date: 1961-03-28
Anticipated expiration: 1978-03-28

Description

March 28, 1961 R. SMILGES 2,976,378

HYDRAULIC CONTROL MEANS Original Filed Jan. 16, 1956 4 Sheets-Sheet 1 mmvro e. ROBERT SMILGE AGENT March 28, 1961 R. SMILGES 2, 7 ,878

HYDRAULIC CONTROL MEANS Original Filed Jan. 16, 1956 4 Sheets-Sheet 2 INVENTOR. ROBERT SMILGES AGENT March 28, 1961 R. SMILGES 2,976,878

HYDRAULIC CONTROL MEANS Original Filed Jan. 16, 1956 4 Sheets-Sheet 4 INVENTQR. ROBERT SMiLGES- AGENT United States Patent ice HYDRAULIC CQN'IROLv Robert Smilges, Buffalo, N.Y;, assignor to American latter is opefatiiigto move 'the rain at a high speed:

' -Brake Shoe'Compauy, New York, N.Y., a corporation of Delaware 16, 1956, Set. 5,59,43,25,

Original application. Jan; D

now Patent. No. 2,927,558,.dated Mar- 8; 19.60,... vided and this application Apr;

7 Claims. er o-1410s) This invention relates to hydraulic-apparatuses it maybe applied with-facility: andiadvantages-zto hydrau ic energy and in which a low horsepower motorr'nay-be employed asthe primc mover. r

Another object of'-'the invention is 'to provide' jim added to the hydraulic liquidbeing supplied to said motor to increase. speed of operation of: the. latter. I Another objectof theinvention is to. provide improved; vaives mctur for the purposes set forth in the-. fo're going objects. which-includes. a spool which is moved from. one position toanotherby difierent pressures created at itsopposi'teiendsby hydraulic liquid flowing through itand-I-ing lithere isiinproved means for causing said dilietehtQressures...

Still another object arms invention is. to. provide an I provedoruice means for, causing liquid flowing therethrough reate a rerent pressures at opposite sides thereofi w ch. includesa-pair of. orifice. means of different alye; .n1eans..bet-ween them responsive to. fi iinidapplied to the firstorifice means. to djandsmaller orifice means. i er e and. advantages, of the present invenron be apparentlffrom the following; description, reference eing tome-accompanying drawings wherex in.a.preferredfiorm, embodiment of the invention is proved apparatus which ir'nparts an improvedfmodeof operation to the ram of a hydraulic press, for example, andwhich is fully automatic"inlcontrolling: the operation of the press rain during; each stroke-or cy'cleaof th'e latter once the stroke or cycle is initiated f i Anotherobject of the invention is to provide irn} proy'ed'apparatus in a hydraulic press, for eXarnp1e,where.- by the press ram is caused'to'. descend at a rapidrate until it engages work on the press. bed and 1111611310 descend at a slower orwo-rking rate while increasirig its working pressure to a predetermined limit and-.when

such pressure is reached to reverse its direction of travel and travel at a high rate of speed .to. its'stalrt'ingpo'sition." a H Another object ofthe invention is toprovide improved apparatus as set forth in" the foregoing ob 'jectfwherein the press ram maybe caused to:'dwell "againstrthework after said predetermined ram pressure has been reached and in which, after said dwell period is completed the ram returns to its starting position. a'tgta high rate of speed.

Another object of the invention is to provide improved hydraulic apparatus for operating the ram of a press, for example, wherein the'rarn is operatedibytwo separate volumes of hydraulic liquid derived trom two .Eis ll and n clearly showm;

. Injthe.accompanyingdrawings: Fi-g l. is aside viewer a-hydraulicpress including the features of the invention, the view'showing thefpress r messsiigeqw ich secdon i r k nonli +1 of Big. 2 lookinginithe direetionlof the. arrows; I

. Zidsaffrbnt, view of the. hydraulic. press; 'seen'in Fig. l with the frame broken awayfto the plane indicated by the1i 1 1e;2t.2.inBig.v 1;.

Fig; 3 isa view, in plan of the hydraulic press seen, in

- Figs, 4;. 5, and 6. are diagrammatic. views. showingthe structure of thehydraulic apparatus or power unit. of

thefpressseen inFigs. 1 2 and 3 and illustrating itsnovel features and,operation.

a This'application is Qadivision of my copending application. Serial No.4 55.9.,438, filed January 16,. 1956, n w

Patent No. 2,927,558 dated March 8, 196.0 for Hydraulic Press. and Control Means I The hydraulic pressshown innFigsfl through} I drawings has a frame, 20 of the'open gapor-O Ape which may; be. r rmeaa .by casting or by fabricatidn from plates which are cut and shaped and then welded intoan; integral unit. v,The frame 20 is hollow forthe purposeor receiving and housing the hydraulicfippa atn's or power unit zlvandthe electric motor 22. of the press andit -includes-a bed '23,-an upright open backed portion Mvand aheadportion 25. which extends from the top of; the. upright back portionv 24 forwardly over the. bed

' 23.1.} -T he" bottom. part of the upright .portion 24 forms or power unit 21 of the press.

sources and which volumes of liquid are first.[merged and directed to the ram motor to cause the mm to travel toward the press bed at a high rateof spee'd; then to separate to cause one of said volumes of liquid .to be directed to said' ram'motor to'do the pressing work; and.

then to re-rnerge and be re-direct'edto the; ram: mOtorto cause it to return the ram to its startingposition ata high r'ate'of speed. V 3

Another object of the invention 'isito-provide improved "apparatus. asset forth in the foregoingobje'ct; andwherein. hydraulic fluid displaced by therarn motor ;when, the :2:-

.after, but it-is pointed em. shaft, whichiorrns a tank or reservoir 26 for storing hydraulicliquid,. preferablyoil, which is employed in the hydraulic apparatus As clearly shown in Figs. 1 through 3. of. the drawings, the hydraulic apparatus orpower unit 21 of the:press is a compact assembly which is contained substantially wholly-within the headportiorr .25. of the frame .21 and above the vhed. 23. I The powerunit 21. inclndesja body, casing .orfhousing formedof {two separate housings or "c ingsr'n e ysia b asin s? housing 2 r. ap p 28 and a'body, casing-tor housipgiiior contro1 -mecha-' sm an eh ul s llro e ta mo -I power un t .W be scr e in de a 1minherei thatfit includes 34 Q 32 of. theprss andjth so mounted in the head portion 25 of frame 20 that the ram 32 thereof projects downwardly through the bottom wall of the head portion 25 and extends toward the center of the bed 23. Hydraulic liquid is supplied to and exhausted from the power unit 21 by a supply conduit '33 and a drain conduit 34 which extend into the tank or reservoir 26, The electric motor 22 is mounted in the upper portion of the upright frame portion 24 above the tank or reservoir 26 by brackets 35 and it drives the pump 28 through sheaves and a belt 36.

The hydraulic apparatus or power unit 21 of the press is shown diagrammatically in Figs. 4, and 6. This apparatus includes the hydraulically operated press ram 32 which, as shown, is formed by the piston rod of the reciprocatory hydraulic ram operating motor 31. Motor 31 includes a cylinder 37 and a piston 38. The hydraulic apparatus or power unit 21 also includes the control mechanism indicated generally by the numeral 30, the pump 28 which is driven by the electric motor 22 and the reservoir or tank 26.

The control mechanism 30 and the ram motor 31 are contained Within the body, casing or housing 29 which is formed by a body or casting 38' and a cap 39 secured ume of liquid to line 64 is approximately two gallons per minute. While pump 28 is herein shown and de scribed as one unit having dual outlets, it is to be understood that two separate pumps may be employed if desired.

As shown in Fig. 4, hydraulic liquid flows from the reservoir or tank 26 through the conduit 33 to the pump 28 where it is divided as aforesaid and flows to

lines

63 and 64 under pressure. Liquid from the low volume output port of pump 28 flows through line 63 to groove 45 in sleeve 41 and from this groove 45 it passes to the interior of the upper end of spool 50 and also to a conduit, line or passage 65, the valve 61, a conduit, line or passage 66 to groove 46 in sleeve 41, and through an annular groove 67 in spool 50 to groove 47 insleeve 41. From groove 47 liquid flows through a conduit, line or pipe 68 to conduit, line or pipe 64 where it combines or merges with liquid discharged from the high volume output port of pump 28. Because pressure of together in fluid tight relation by bolts or screws," not shown, and a gasket 40. The'body 38' includes'a central bore in which a sleeve 41 is pressed axially and clamped against a shoulder 42 in body 38' by a'shoulder 43 surrounding the mouth of a stepped bore 44 in cap 39. Sleeve 41 includes a plurality of external channels or

grooves

45, 46, 47, 48 and 49 separated by lands which engage the walls of the bore in body 38' whereby the channels 45 through 49 form passages through which hydraulic fluid may pass circumferentially around the sleeve 41. Each of the channels or grooves 45 through 49 is connected to the interior of the sleeve 41 through ports and these ports are controlled by lands and grooves on a hollow valve piston or spool 50 which is slidable axially within the sleeve 41.

, I Spool 50 includes an internal wall or partition which forms an orifice 51 and a valve seat against which a poppet 52 having a central orifice 53 seats. Poppet 52 is preferably, but not necessarily, made of nylon and it is urged by a spring 54 contained within the lower portion of the spool 50 to seat against the partition as above described. This spring 54 acts through the poppet 52 to urge the spool upwardly to the position shown in Fig. 4 of the drawings where the upper end of spool 50 abuts a shoulder on an unloading piston '55 which is slidably positioned in the upper end of the bore in sleeve 41.

' The unloading piston 55 includes an extension 56 which extends into the vupper end of the spool 50 and which is slotted at 57 to receive a pin 58'which extends therethrough and is secured to the spool 50. The

function of the lost motion connection provided by the pin 58 and slot 57 will be made apparent hereinafter. Unloading piston is also provided with an annular 1ip'59 adapted to abut the upper end of sleeve '41 to limit its inward movement into the sleeve 41 'and it is urged downwardly to the position shown in Fig. 4 of the drawings by a compression spring 60 contained within the bore 44 of cap 39. The body 38" also houses a be stated that the pump 28 has two outlet or output ports 1 which are connected respectively to inlets; conduits or lines 63and 64 formed in the body 38 and that the volume of fluid delivered to the lines 63 and 64are preferably,

but not necessarily, different. In one embodiment'of the the liquid will pass through the partition in valve spool 50, the spring 54 will maintain the valve spool 50 in the position shown in Fig. 4 of the drawings until the valve 61 is closed.

The liquid flowing from conduit 68, as previously mentioned, merges or mixes with the liquid flowing in conduit 64 and thus, at this time, the total or combined output volume of pump 28 is supplied through conduit 64 to the bottom of cylinder 37 to elevate the piston 38 and ram 32. When piston 38 is in its uppermost position, liquid entering the cylinder 37 from conduit 64 is discharged from the cylinder 37 through a conduit 69 which leads to groove 49 in sleeve 41. From groove 49, this liquid flows through a groove or channel70in spool 50 to channelor groove 48 in sleeve 41v and throng drain or exhaust line 34 to reservoir or tank 26.

When-it is desired to start. the ram 32 .to descend toward the press bed, the solenoid 62 of valve'61 is energized to cause valve 61 to-close. When valve 61 closes, hydraulic liquid flowing inconduit 63 passes through groove 45 in sleeve 41 and from this groove to the interior of the upper end of valve spool 50 and also to valve 61 where its flow is blocked. The pressure of;the fluid flowing from groove 45 to the interior of valve spool 50, however, will increase and force the fluid to flow through the orifice 51 in spool 50 and the orifice 53 in poppet 52 to the interior of the lower portion of spool 50. From the bottom of spool 50, liquid flows through by-pass conduit 71 through a check valve 76, conduit 66, groove 46, groove 67 in spool 50 to groove 47, and conduit 68 to conduit 64. ,The liquid flowing through

orifices

51 and 53, of course, creates a pressure difierential between the upper and lower ends of'the valve spool 50 and the spool 50 is thereby causedto compress the spring 54 and move'spool 50 downwardly to the position shown in Fig. 5 of the drawings. This action or movement of the spool 50 occurs very quickly when liquid flows through the orifices. 51 and53. .After spool 50 moves downwardly, liquid flows from the bottom of spool 50 through openings or ports in the bottom. of sleeve 41 to channel 70 in spool 50, groove 49 in sleeve 41 and conduit 69 to the top of cylinder 37 and piston 38.

When the valve. spool 50 is moved downwardly, as above-described, to the position shown in Fig. 5, hydraulic liquid flowing from the high volume output port of pump 28in conduit 64 travels through conduit 68 to groove 47 in sleeve 41 and from it through a check valve -72*and conduit.71 to the bottom of spool. 50 where it combines or merges with. the output from the low volume output port of pump 28 and flows through the passages "invention, the output volume of liquidto'line 63 is approximately one gallon'per' minute and the output voldescribed .to the top of the cylinder 37 and piston 38. This liquid, of course, will" move the piston 38 downwardly and the liquid below the piston 38 will be expelled through conduit 64 and becombined or merged with the-fluid entering the conduit 64 from the high volume output port of pump 28.. It will thus beqseen and 53 and th spool ho y i Fi 4. i the therein 32 will berhoved at a rapidrate or speedto its up position and the parts" of the control unit2 1 will .be placedjin readiness for the next. cycle of operation of we rs that the pi'stoii 38, whieh is an unb alanc'e'dpistonj, be moved downwardly rapidly since the 'combined output volumes oi -both of the output ports of; pump 2-8 and the output from the bottom of. cylinder and's upplied to the top of the'piston 38'. I

It should be notedthat once the spool 50jhas been moved to theposition shown in Fig. '5 that valve 61 may; be openedsince the output line 66 thereof isclosed by, the isolation of groove 46 from the interiorof; sleeve 41by-a land on the spool 50. wIn other words, therea're present two valves connected in series and either may function to block the flow of liquid from the groove and the upper end of valve spool It should also henoted that the maximum pressure in thetop'o'f cylinder 37' is controlled by an adjustable relief valve 73.

The-ram 32 will travel freely toward the press bed 23 at a fast traverse speed until the ram 32 engages work on the bed, for example, after which, of course, very little liquid will be displaced from the bottom of cylinder 37. The resistance offered to the movement of the ram, 32' upon engaging work on the bed 23 will cause thepressure ijnthe cylinder 37 above the piston to increase and increasein pressure will be reflected to the top. of spool 50 to cause t e unloading piston to move upwardly to compress spring and 'restu'p'ona shoulder orstop, in the bore 44 in eap 39. V As the unloading piston, 55 moves upwardly, the lost motion-connectionprovided by the slot 57 in extension 56. and: pin 58 litts shown, in Fig. 6. of. the drawings, and when the parts of the control-unit 21 are in the position shown in said Fig. 6 only the pressuresupplied from the low volumeoutput port of pump 28through conduit 63 is. applied to thetop of the piston 38. For this reason, all of theenergy of motor employed to drive pump 28 against-the. pressure of its low volume .output'po'rt in conduit 63,. V t i or w .Upon the movement of valve spool '50 to the position shown iufig. 6, all of thehigh volumejoutput otpump gti flowing line 64gas'wellas'thechaniber; formed in the bottomof cylinder'37 b'elow piston ,38 i stconnected togtanlglo through the conduit 68, groove-I47 in, sleeve 141,,a groove74- in spool "50, groove 48v in sleeve 41- and drain port or conduit 3'4.' At this time all offthe low volume pump output'flowing in'conduit 63. to the top of'pis'ton 38" and the entiretop areaof said piston is efiective to do work because thesmaller; bot-tom area thereof is exposed 'to tank pressure as-described above.

The maximumpressure that can build up in the cyliua der 37 above piston 38 is controlled by the adjustable relief valve 73. When the ram, ance in. its movement toward the press bed 23" sufiicie'nt to causevalve 73 to open, the rammovement stops and the full flow of liquid from the low volume output'por't ofpump 2 8 flowiugin cofduit' 63 isdire'cted through groove 45, line 65, valve'fil, cond t 6 6', groove 46' to reliefyalve 73, and drain conduit 34 to tank 26. Because the motion'of ram 32' has stopped, therewill be substantially no flow of liquid through the orifices-:51 v,

50 will 'be'returned to the position drawings by the spring54- whereby the-Pre s I' As previously set forth, the pump 28 delivers two output volumes and as stated, in oneembodimentof the invention these output volumes are one and two gallons perminute, it has been as the oi tput pressures of the pump increase the output volumes will decrease due toineiiicienciesv of theppump leakages of fluid therein. Becauseof-zthis fact, the

- "p'opp 52 includ ng the orifice-'53, is providedin spool 50; The orifice 53in poppet 52 is ot lesscdiametersthau vis directed found in practice, however, that 37 v are merged the valve spool 50-to the position a substantially 32 encounters a resjistflowing to the top motor cylinder 37 'high.;rate .of speed. I I v While the form: of embodiment of the present invenis .togbe iunderstood that other the on'fice 51 in the partition in spool 50 and when the outputfpress'ure of the 1OW' volume output port offpuinp 2:8"is low and valve 61 is first-closed, described: in' connection with Fig. 1', the volume and pressure of liquid; of spool 50 is suchthat it will: pass through the orifice 51 and lift-the poppet 52 off of its seat while moving the spool 50 downwardly without lift-=- ing the; unloading spool 55. As the volume of liquid pumped to the top of-spool 50 decreases-due to increased pressure, the poppet- 52 whichis being urged to its closed position causes orifice 53 to become efiective-to restrict the flow of "liquid and thereby provide the necessary pressure differential between'the opposite ends-'ofspool 50-to hold it in the position seen in Fig. 5. It will thus be seen that the poppet 52 and

orifices

51 and 53 c0 1 operate to provide an assembly includingvariable orifice means which is responsive to provide the necessary pressure differential atopposite ends of' the. spool .50 even though both the pressure and volume of liquid supplied to the top or spool 50 may vary. 1

It is pointed out that if the valve 61 is held in its closed position that the automatic reversal feature of the apparatuswhic occurs when valve 73 opens will vented from becoming operativeuntil th'e valve 61 is permitted to open; ;--Thus, a press operator by keeping the solen0id'62 energized may cause the ram 20 todwell upon the work. Y

From the foregoing invention provides" a control unit prayed with facility, to -cause thepress to tracted position and that to descripton, it wi llbe seen that the 21 which may be emfor example, in a hydraulic press idle with its ram held ina reinitiate a cycle of operation oftheram it is necessary onlyto'close the valve 61 momentarily, or until the valve spool 50 shifts from the position-see'n in Fig. 4 to the positionseen in Fig. 5 of the drawingsand that thereafter'theacycle of operation, namely-'arapid approach of the rain to the work, a buildup of ramipressui'e'to the setting of valve 73, and a tapidreturnofthe ram to. its .up or press idling .posit 'o'n- 1 lt-will alsobeobviousithat when the ram. is travelling toward the work thatboth volumes- 0f liquid pumped by the pump and liquid displacedfrom below the piston '38 are mergedand supplied to the top of cylinder 37 to force the piston 38 downwaidly'at a high .rate of-speed and that-when in its meets "sufficient resistance to increase the hydraulic pressure: above the piston 38 and spoo1 50tolift the unloading piston 5'5 and spool 50,.that only thefsmaller output volun'ieof'pump 28 flowing in conduit 63. is applied to the top of piston 38 and the higher outputvolume or pump 28 fiowinginconduit 64fand the bottom of the are connectedto exhaust. 'Thiscondition will continueto exist until the hydraulic pressure above thetpiston v38 increases and opens valve 7-3zat which time the spring 54 will return :spool. 50 to the position seen in Fig.4 of the; drawings wherein: both volumes of hyd'raulic liquid being pumped by pump 28 will be merged andsupplied to thebottom of piston .38 to elevate or retract the :ram 32 at a-high rate of speed. It will be apparent from the above'that thisiuvention aprovides 'an'ir'nproved hydraulic-apparatus for operating a and then to re-merge and be re-directed to the ram motor toacause it to returnv the-ram to its starting position at a tionZ-as herein disclosed constitutes a preferred form, it 4 m h beadopt tl, all commgwithinthe sco e.oftheclaimstw ist glodgw t be pre downward movement'theram 32 a 1..A :valve for directing the flow of two separate volumes ofihydraulic liquid from two sources including a-body having a first and a second inlet means and a first and a second outlet means, means forming a bore in said body, means forming a plurality of ports spaced axially along said. bore including ports connected with said inlet and outlet means and a drain port, spool means in said bore for selectively interconnecting said port means, said spool means when in one position in said bore interconnecting ports to direct said separate volumes of liquid to said first outlet means, means for causing an increase in .the pressure of one of said volumes of liquid to shift said spool means to a different position insaid boreethereby directing both of said volumes of liquid to the second of said outlet means, means respon= sive to the pressure of liquid at said second outlet means for causing said spool means to shift to another position in said bore for directing said one volume of liquid to said second outlet means and the other volume of liquid to saiddrain port, and means responsive to a further increase in pressure of said'one volume of liquid to shift said spool means again to direct said volumes of liquid to said first outlet means. j 2. A valve for directing the flow of two separate volumes of hydraulic liquid from two sources including a body having a first and a second inlet means and a first and a second outlet means, means forming a borein said body, means forming a plurality of ports spaced axially along said bore including ports connected with said inlet and outlet means and a drain port, spool means in said bore for selectively interconnecting said port means, said spool means when in one position in said bore intercon-v necting ports to direct said separate volumes of liquid to said first outlet means, means for causing an increase in the pressure of. one of said volumes of liquid to shift said spool'means to a different position in said bore therebydirecting both of s-aidlvolumes of liquid to the second "of said outletmeans, and means responsive to the pressure of liquid at said second outlet means for causing said spool means'to shift to another position in said bore for directing said one volume of liquid-to said second outlet means and the other volume of liquid to said drain port. 3. Apparatus for directing the flow of two separate volumes of hydraulic liquid from two sources including a'first and a second conduit meansfor conducting said two volumes of liquid, a first and a second outlet conduit means for receiving said liquid and a drain conduit, valve means for selectively interconnecting said conduits and operatable in one position to direct saidvolumes to said first outlet conduit, means for causing an increase in pressure in one of said volumesof liquid for shifting said valve means'thereby directing said volumes to said second outlet conduit, means responsive to an increase in the pressure of said one volume of liquid for causing said valve to direct said'one volume of liquid to said second outlet conduit and the other of said volumes. to said drain conduit, and means responsiveto a further increase in pressure of said one volume of liquid to cause saidlvalve again to-direct said volumesof liquid to said first outlet conduit.

4. Apparatus for directing the How of two separate volumes of hydraulic liquid from two sources including a first-and a second conduit means for conducting said two volumes of liquid, a first and a second outlet conduit means forreceivingsaid liquid and a drain conduit, valve means for selectively interconnecting said conduits and operatable in one position to direct said volumes'to said :first outlet conduit, means for causing an increase in pressure in one ofsaid volumes of liquid to shift said valve means thereby directing said'volumes to said second outlet conduit, and another means responsive to a further "increase intli'e pres'sur'e'of said one volume of liquid for causing saidv'alv'e to direct said onevolume of liquid :to seat second outlet conduit and the other of-said volumes to'said drain'conduit;

smears separate volumes of liquid, a first and second outlet conduit means for saidliquid and a drain conduit, valve means including ports and a spool for selectively intercom nectingsaid conduits and operatable in a first position to direct said volumes from said inlet conduits to said first outlet conduit and operatable in a second position to direct liquid from. said inlet conduits to said second outlet conduit and operataible in a third position to direct liquid from one of said inlet conduits to one of said outlet conduits and the other inlet conduit to said drain conduit, means resiliently urging said spool to said first position, means in said spool forming an orifice through which liquid can flow from one end of said spool to the other, said orifice causing liquid passing therethrough to create difierent pressures at opposite ends of said spool for shifting said spool to said second position, liquid conducting means for conducting liquid from said one end of said spool to by passv said orifice, a first valve means for closing said liquid conducting means, a second valve means connected in series with said first valve means for closing said -'liquid conducting means, said second valve means being closed by shifting of said spool to said second position, pressure operated means responsive to an increase in pressure of the liquid at said one end of said spool for moving said spool to said third position, and a relief valvetresponsive to pressure at said one end of said spool and operatable to relieve said pressure whereby said resilient means'movessaid spool to said first position.

6. In avalve apparatus for directing the flow of two separate volumes of hydraulic liquid from two sources including .a first and second inlet conduit means for said separate volumes of liquid, a first and secondoutlet conduituneans for said liquid and a drain conduit, valve means including ports and a spool for selectively interconnecting-saidconduits and operatable in a first position to direct said volumes fromsaid inlet conduits to said butI'et-conduitand operatable in a second position'to direct=liquidrfrom said inlet conduits to said second out let conduit. and operatable ina third'position to direct liquid from one of said inlet conduits to one oflsaid outlet conduits and the other inlet conduit to said drain conduit, means resiliently urging said spool to said first position, means in said spool forming an orifice through Which-liquid can flow from one end of said spool to the other, said orifice causing liquid passing therethrough to create different pressures at opposite ends of said'spool forshifting said spool to said second position, fluid conducting means for conducting liquid from. said one end of said spool to by-pass said orifice, valve means for closing said fluid conducting means, pressure operated means responsive to an increase in pressure of the liquid at said :one end-of said spool for moving said spool to'said third -.position,and a relief valve responsive to pressure at said *to direct said-volumes from said inlet conduits to said first outlet conduit and operatable in a second position to directliquid-from said1inlet conduits, to said second outlet conduit and operatable in a third position to direct .liquidfrom one of said inlet conduits to oneof saidou tlet conduits and the other inletconduittosaid drain conduit, means resiliently urging said spool to said first posiition means in said spool forming an orifice through which d of said spool to the other, References Cited in the file of this patent liquid can flow from one en said orifice causing liquid passing therethrough to create UNITED STATES PATENTS dififerent pressures at opposite ends of said spool for shlfting said spool to said second position, fluid conducting 348,146 Glbbi 241 1912 means for conducting liquid from said one end of said 5 MurPnY Sept-10, 1941 spool to by-pass said orifice, valve means for closing 2,655,930 Prowler et a1 1953 Said fluid conducting means, and pressure operated means 2,716,997 Crookston P 1955 responsive to an increase in pressure of the liquid at said 2,745,253 Towlef et a1 y 1955 one end of said spool for moving said spool to said third 2,7 ,3 Peterson SP 9 10 2,853,159 Kuhn Sept. 23, 1958 position.