USRE23682E

USRE23682E - Unloading valve

Info

Publication number: USRE23682E
Authority: US
Publication date: 1953-07-07

Description

July 7, 1953 INVENTOR e rfa/A904 5mm ATTORNEYS UNLoanmc vnu;

R. sTl-:vENsoN UNLOADING VALVE original Filed June' 27,1944

A L* why vulve lI-RUYII Ressued July 7, 1953 UNLOADING VALVE Robert Stevenson, East Greenwich, R. I., assgnor to Merit Engineering, Inc., aY corporation of Rhode Island Original No. 2,545,712, dated March 20, 1951, Se-

rial No. 542,411, June 27, 1944. Application for reissue March 18, 1953, Serial No. 343,273

Matter enclosed in heavy brackets appears in the original patent but forms no part of this 11 Claims.

reissue specication;

AThis invention relates to an unloading Valve for use in a system in which the uid pressure may be maintained without constant action of the fluid pump.

One of the objects of this invention is to provide .a valve through which fluid may pass to supply pressure for transfer of the fluid and yet short circuit the duid flow back to the reservoir whereby the energy required by the pump will be relieved.

lAnother object of this invention is to provide a valve in which the fluid passing through the valve will automatically short circuit when a predetermined pressure is reached and thereby relieve the pump which operates on the Valve from the work which it has to do when this short circuiting arrangement is not cut in.

- Another object of this invention is to provide a quick operating valve and consequently one in which the control of the system may be closely obtained.

Another object of the invention is to provide no sliding packing which is exposed to the high pressure fluid when the valve is in unloading position and it is desired to maintain the system at high pressure without subjecting the pump to high working conditions.

Another object of the invention is to provide two rigid seats for the valve against which the high pressure works.

Another object of this invention is to p-rovide an arrangement whereby the Valve may be easily and quickly adjusted.

Another object of this invention is to provide a cartridge which may be removed from the valve without disconnecting the valve from its communicating conduits.

Another object of this invention is to provide a removable cartridge which may be. preadjusted and merely insert it into the valve for a predetermined value of operation of the valve or which may be interchanged with another cartridge for a change of such predetermined adjustment.

With these and other objects in View, the invention consists of certain novel features of construction, as will be more fully described and particularly pointed out in the appended claims.

1n the accompanying drawings:

.. Fig. 1 is a sectional view through the valve;

Fig. 2 is a sectional view through a removable unit which may be inserted in the valve body; and

Fig. 3 is a diagrammatic view illustrating a systemv employing the unloading valve.

i yIn proceeding with this invention I provide a matter printed in italics indicates the additions made by reissue.

valve body which has a port to connect with a high pressure supply and a port to connect with the work with a passageway between these ports. A low pressure .port is also provided in the valve with a conduit connecting with a passageway for the high pressure fluid. These passageways are controlled by a main valve with a check valve therein by an-arrangement such that the high pressure will press upon opposite ends of the valve, the surfaces of said valve which are exposed to the pressure being of such relative diameters that the unbalanced pressure due to the differential of the diameters determines the direction in which the valve will be moved. A spring supplements the larger diameter and the pressure on this larger diameter is so controlled that when pressure is permitted upon this larger diameter the valve will be closed but when the control acts to remove this pressure on this larger diameter then the pressure on the smaller diameter will overcome the springend cause the valve to open. This control is by a predetermined arrangement so that automatic operation will be had, the arrangement being such that the main valve will open at a predetermined high pressure and will close at a predetermined lower pressure. When the main valve is open iluid pressure may short circuit to the low pressure port without being spring opposed and less work need be done by the means which supply the fluid to the high pressure port and also there is no valve vibration.

A system in which the valve is used is illustrated in Fig. 3 wherein a reservoir shown from which a pump takes liquid fo-r supplying it to a cylinder A at either end of the cylinder by reason of the four-way valve B. An accumulator may be in the line for maintaining a somewhat equal pressure. As the fluid is supplied at one end of the cylinder to move the piston therein, fluid is extracted from the opposite end of the cylinder and returned to the reservoir. My unloading valve Ill is located in this line between the pump and the work in the location illustrated in this gure and a return line C is provided from another port of the valve to the reservoir. One port 20 of the valve is connected to the pump by conduit E, a second port I8 is connected to the work by conduit D and another port 23 is connected by the return line C to the reservoir. The supply from conduit E will be directed to either conduit C or D. In oper-ation We may assume that it is desired to maintain from 800 pounds to 1000 pounds pressure for the work required. This pressure is only needed when there is an actual movement of the piston in the cylinder. Consequently when no movement occurs the pressure rapidly builds up. When this pressure builds'up to 1000 pounds my unloading valve will automatically operate so asv to switch the circulation from the work to the by-pass through conduit C back to the reservoir,v -thus reducing the load on the pump considerably.

With reference to the drawings, II) designates a valve body formed of a block of metal which has a main bore II for the main valve threaded as at I2 and enlarged as at I3 at one end while more restricted portions I4 and I6 provide shoulders I5 and I1. The portion vlli of this bore provides a port I8 for a high pressure discharge which may be threaded as at I9 for connection of some suitable `conduit `such as D leading to the work. The bodymay have an outwardly projecting boss 22 in which a pressure supply port is located which is provided with internal threads 2I for connection to some suitable conduit E to the pump and which communicates with the bore I I. provided in this boss having threads 24 for connection to some suitable conduit C returning to f.

the reservoir. main bore II.

A smaller bore 25 is also provided in the body I6, the axis ofvwhich is parallel to the bore II. This bore is-of the same size throughout `its extent fromV one end of the body to the other and receives the-complete unit designated generally 26 and shown by itself in Fig. 2 in this bore which will be more fully hereinafter described. The bore '25 connects with the main bore through a passage 21 adjacent one end and through a passage 28 adjacent the other end of the valve body. f

- In the main valve bore II, I position a block This port also connects with the 30 of generally tubular formation [which at its end 3l] and having a portion of the bore thereof reduced as at 30. The end 31 of the block engages the shoulder I1, while a soft packing 32 serves to seal this end of the block in the bore Il. A plurality of openings 33 extending laterally of the block communicate with the annular chamber 34 formed by the reducedportion of the block between itself and the bore Il at a location so that this annular chamber communicates with the high pressure port 26 and the bore Y30. A suitable soft packing 35 serves to seal the block with the bore II on the opposite side of this annular chamber 34.V A valve seat 36 is provided at one end of the reduced bore V30" against v which the main valve is seated to close communication between the supply port and the return port. A valve seat 36 is provided at the other end of the bore 30. The bore of larger diameter of this block [at the junction of the inner surface of the bore and against which the main valve is seated. The inner surface at the opposite end of'fthis'blockj'designated 31 provides a sliding guide for one end ofthe valve.

' A sleeve 38 has threaded engagement with the threads I2 of bore II and itsend engages the block 36 so as to maintain thisv block firmly against the vshoulder' I1 rigidly in place in the valve body. The sleeve has an internal bore 3B of a size substantially larger in diameter than the diameter of the valve seat 36 and infthis bore is located the main valve 40. Themain valve 40 .has a tapered surface 4I to engage the valve seat 36 and a flange 42 to slidingly engage the `bore 39 of the sleeve 38. A soft packing v43 is provided to prevent the escape of A low pressure port 23 is also 4 fluid between these engaging surfaces. The valve is also provided with an end portion 44 slidingly engaging the surface 31 of the block 30 and connected to the reduced end of the valve by a stud 45 extending axially through the valve and secured by nut and check nut 46 and 41. This end v'portion 44 has a surface area normally exposed the bore 25.

to the supply pressure in the bore 37 which is connected to the supply 20 through the smaller bore 30 which providesa` valve seat 36' with which thev end portion 44 engages when the main valve 40 is 017 its seat 41. When the main valve is closed on the seat 41 the effective area of the end portion, 44 is balanced. The valve is provided With a central recess 48 for the reception of a coil spring 49 which acts to force the valve toward its seat`41 by engagementwith the abutment surface 49 of the plug 56;y

VThis plug 50 is threaded as at 5I into the end of the sleeve 38. The hollow interior of the reduced portion of this plug connects with theannular chamber 52 between the head of the plug and the end of the sleeve by reason of a plurality of openings 53 extending through the stem of the plug. This annular chamber 52 is in communication with the conduit 28 so that liquid may be supplied through this passage 28 to the chamber 54 on the enlarged end of the valve.

A suitable soft packing seal 55 is provided in the sleeve at one side of the annular chamber k52 and a softpacking 56'is provided in the plug on the other side of the annular chamber 52 to prevent the escape 'of rthe high pressure fluid along these surfaces. Y

The unit 25 which is inserted in the bore comprises a sleeve 60 of a size to slide within the bore 25. The sleeve is reduced in diameter at certain points along its extent as at 6I so as to provide an annular chamber 62 between it and Openings 63 from this chamber62 communicate with the bore 64 and bore 65 in the sleeve, which latter bore is in communication with the longitudinally extending channel or recess 66 which in'turn communicates through opening 61 with the annular chamber 68 surrounding the sleeve 38 which is in communication with the low pressure port 23 and also the surface of the valve between the valve seat and the head or flange 42. Another recess 10 in this sleeve communicates with the bore 65 through the conduit 1I and through port 12 with the space about the plug 13 and thence through the central channel 14 with the annular chamber 15, through openings 16', which annular chamber 15 is in connection with the conduit 2B and the chamber 52.

The upper end of the bore 65 provides a valve seat 16 against which the inclined surface '11 of a valve 18 may engage to close this bore 65. The flared end 13 of the valve engages 'the borel 64 and isguided along this surface. Openings through this flared portion of the valve serve for free communication of the high pressure fluid to the inner conical surface of this flared portion and serve to` balance all portions of this `end of the valve except the diameter which engages the valve seat. The valve immediately below the valve seat is of reduced diameter but at a point below conduit 1I the valvehas a portion 8| slidingly engaging the bore 65. The end of the valve is reduced as at 82 and` 83 to project through an opening 84 in a wall which extends laterally across the. sleeve. This opening84 serves as a passage for fluid to the recess. 66 and is closed by a ball 85 which is pressed by the plunger 13 to seating position through means of a coil spring 86 having one end engaging the abutment 81 threaded as at 88 for movement longitudinally of the bore 99.

The sleeve 60 is internally threaded at its opposite ends as at 90 and 9| into which plugs 92 and 93 may threadingly engage. The heads of these plugs are sealed by soft p-ackings 94 and 95 which are located beneath the heads of these plugs and the ends of the sleeves 60. These closure plugs also serve to abuttingly engage the outer end of the body l0 where the bore 25 emerges to the end surfaces. Slots 96 in these plugs serve to assist in turning them into position While an opening 91 may be used for wiring to the opening 98 in the ange of the closure 50 so to prevent relative turning of these parts with reference to each other and to the body.

The guided end portion of the main valve is provided with a check valve |06 which is forced to its seat by a spring |0| abutting the perforated plate |02 secured in the end of the main valve. Pressure is communicated from. the inlet high pressure port I8, also by reason of the

conduits

21, 65,1I, 10,12,14, 16, 15, 28, 52, 53 and 54, high pressure is transferred from one end of the main valve 40 on one side of the valve seat 36 to the other end of the valve at the other side of the valve seat 36. The diameter of the valve head 42 at one end of the valve determines the closing pressure which Will be applied on the valve which is assisted by the sp-ring 49. Pressure exerted tending to open this valve presses on an area of the valve equal to the diameter of the seat 36. The remainder of this end of the valve is all in balanced relation. A complete balance may be provided using pressure of spring 46 alone for closing.

It is so arranged that if the pressure on the area. 42 of the valve is cut off, then the pressure on the opposite end of the valve will overcome the pressure of the spring 49. and open the valve. The check valve |00 prevents pressure from the line D escaping to the return C. The automatic cut-off of the pressure on the area 42 is provided by the pilot valve in the bore and which is a separate unit as shown in Fig. 2.

The ball 85 normally closes the opening 84 and at the same time the spring which forces this ball to its seat also forces the valve 18 from its seat 16 so that it is normally open.

When the ball 85 is seated, the surface area `thereof exposed to high pressure liquid is such as to provide an unbalanced force acting on the ball in a direction tending to move the same towards its seat. The surface area of the ball exposed to this force is an area equal to the area of the opening 84. The spring 86 supplements this force. The surface area of the valve 18 subjected to pressures tendingto slidably move the same toward or from its seat is balanced such that the effective area thereon exposed to pressure tending to move the same to its seat, when the ball 85 is seated, is an area equal to the area of the bore 65 minus the area of the opening 84.

The adjustment of the spring 86 is such that it will yield when the pressure reaches top limit of the range. This may be assumed to be 1,000 pounds. Such pressure on the valve 18 will move the same to its seat against opposing pressure on the ball 85 and resistance of spring 86. With the ball valve 85 removed from its seat, fluid will escape through opening 84 and will reduce the pressure opposing the valve 18. l With the valve 1|8 seated, the surface area exposed to pressures 6l' tending to oppose moving the same from its seat is equal to the total area of the bore65 and will maintain the valve closed against the action of spring 86.

When the ball is forced from its closed position liquid may escape through the opening 841 to the recess 66, thence through the opening 61 through the annular chamber 68, and thence to the port 23 and 10W pressure side of the valve. The closure of the valve at 18 prevents high pressure fluid from being sup-plied to chamber 54 and area 42 of the head of the valve. Thus, by the absence of this pressure the main valve will open and the incoming fluid from conduit E` will pass from the port 26 past the valve seat 36 to the port 23 and through conduit C back to the reservoir and this conditio-n will occur until the pressure in thevvork line drops to an extent, say S00 pounds, when the spring 86 will overcome this pressure, open the valve 11, close valve 85, [and open the pilot Valve] and permit liquid to be supplied to the chamber 54 under the higher pressure and consequently press upon this larger diameter of the valve at this end to close the same. Thus the opening pressure and the closing pressure are in- 'versely proportional to the opening area and closing area.

Upon movement of main 'value 40 from the salue seat 36 the tapered surface 44 will move to engage value seat 36, the balanced condition on portion 44 is changed. The larger bore 37 is` now shut o l from the supply pressure, leaving only the diameter of the bore 30', which provides the value seat which thetapered surface 44 engages, exposed to the supply pressure. Thus, the digerence between the diameters of the larger bore 37 and the smaller bore 30 is at once subtracted from the eectiue pressure on the portion 44, tending to move the value 40 upwardly or toward closed position. Further, the pressure upon the valve 40 in the diameter of the bore 39 is subjected to the supply pressure. This supply pressure, however, may decrease materially leaving the discharged pressure acting through the diameter of the bore'37 upon the end portion 44, tending to hold the main value 40 ojf its seat or in open position and which is opposed only by the spring 49. A free flow from port 21 to port 23 will be had even gt low pump pressures without any ualueoibraion. l

A relief valve |05 may be placed in the line El With a return connection F to the reservoir.

I claim:

1. In an unloading valve having a body pro--A vided with a supply port, a discharge port and a return port communicating with the supply port, a main valve normally seated to close communication between said supply port and return port and subjected on one side thereof to the pressure at the supply port tending to unseat said valve and on the other side to the pressure at the discharge port tending to seat said valve, a check valve between the supply and discharge ports for blocking the return of Huid from said discharge port Vso proportioned with reference to the main valve'as to area and spring pressure as to bel unseated when said main valve is seated and seated when said main valve is unseated, a normally unseated second valve for controlling the said iiuid pressure from said discharge port which acts on said main valve, said second valve being lsubjected on one side to the pressure at the discharge port tendingto seat said second valve'` to cutoff said pressure from said discharge port .7` which acts on said main valve, a vent conduit. in said body communicating with said return port for draining upon the seating of said second valve the said pressure from said discharge port which acts on said main valve for creating a differential pressure condition across said main valve to unseat the same in response to the said pressure from the supply port which acts thereon, a third valve for controlling said vent conduit arranged to be normally seated and subjected on one side to the pressure at the discharge port tending to move the same to closed position and engaged on the other side by said second Valve to be unseated thereby upon seating of said second valve and a spring supplementing the said fluid pressure acting on said third valve to oppose closing of said second valve and adjustable means to predetermine the fluid pressure range at which said second valve will be seated or unseated.

2. In an unloading valve, a supply port, a discharge port, a passage for fluid between said ports, a return port communicating with the supply port, a conduit therefrom to said passage v providing a valve seat, amain valve arranged to be normally seated on said seat and subjected on one side thereof to the pressure at the supply port tending to unseat said main valve and on the other side to the pressure at the discharge port tending to seat said valve, a check valve between the supply and discharge ports for blocking the return of fluid from said discharge port so proportioned with reference to the main valve as to area and spring pressure as to be normally unseated when said main valve is seated and seated when said main valve is unseated, a second conduit for supplying fluid from the discharge port to said main valve, a second valve in said second conduit normally unseated and subjected on one side thereof to the fluid pressure in said second conduit tending to seat the same Yto close said second conduit to cut off the fluid from said discharge port to said main valve, a vent conduit from said second conduit to said return port to drain fluid from said second conduit upon seating of said second valve to create a differential pressure condition across said main valve to unseat the same in response to the said pressure from the supply port which acts thereon, a third valve for controlling said vent conduit arranged to be normally seated to close said vent conduit and subjected on one side thereof to the fluid pressure in said second conduit tending to seat said third valve and engaged on the other side by said second valve to be unseated thereby upon seating of said second valve, and a spring supplementing the said `fluid pressure which acts on said third valve to oppose the seating of said second Valve and adjustable to predetermine the fluid pressure range at which said second valve will be seated and said third valve opened.

3. In an unloading valve, a supply port, a discharge port, a passage for fluid between said prtsa return port communicating with the supply port, a conduit therefrom to said passage providing a valve seat, a main valve arranged to be normally seated on said seat and subjected on the high pressure side of said seat to the pressure at the supply port tending to unseat said valve and on the low pressure side of said seat to the pressure at the discharge port tending to seat said main valve, a check valve in said main valve located between the supply and discharge ports for blocking the return of fluid from said discharge port so rproportioned with reference to the main valve as to area and spring pressure as to be seated when said main valve is unseated and unseated when said main valve is seated, a spring on the low pressure side of said seat urging said main valve to seated position, a second conduit from said passage to supply fluid from the said discharge port to said main valve, a second valve in said second conduit normally unseated and subjected on one side thereof to the fluid pressure in said second conduit tending to seat said second valve to close said second conduit to cut oi the uid from said discharge port to said main valve, a vent conduit from said second conduit to said return port to drain fluid from said second conduit upon seating of said second valve to create a differential pressure across said main valve to unseat the same in response to the said pressure from the supply port which acts thereon, a third valve for controlling said vent conduit arranged to be normally seated and engaged on one side thereof by said second valve and unseated thereby upon the seating of said second valve, said third valve being subjected on the other side thereof to the fluid pressure in said second conduit tending to seat the same and oppose seating of said second valve, spring pressure urging said third valve to seated position and adjustable to predetermine the pressure range at which said second valve will be seated and said third valve unseated.

4. In an unloading valve, a supply port, adischarge port, a passage V`for fluid between said ports, a return port communicating with the supply port, a conduit therefrom to said passage providing a Valve seat, a main Valve engaging said seat and arranged to be normally seated and subjected on the high pressure side of said seat to the pressure at'the supply port and on the low pressure side of said seat to the pressure at the discharge port, said valve having a portion thereof slidably extending into said passage and provided with a bore therein communicating with said supply port and said discharge port, a check Valve in said bore between the supply and discharge ports for blocking the return of fluid from said discharge port so proportioned with reference to the main valve as to area and spring pressure as to be seated when said main valve is unseated and unseated when said main valve is seated, a spring on the low pressure side of said seat urging said main valve to seated position, a second conduit from said passage to supply fluid from said discharge port to said main valve, a second valve in said second conduit arranged to be normally unseated and subjected on one side thereof to the fluid pressure in said second conduit tending to seat the same to close said second conduit to cut off the fluid from said discharge port to said main valve, a ventconduit from said second conduit to said return port to drain fluid from said second conduit upon seating of said second valve to create a differential pressure across said main Valve to unseat the same in response to the said pressure at the supply port which acts thereon, a third valve for controlling said vent conduit arranged to be normally seated and engaged on one side thereof by said second valve and unseated thereby upon the seating of said second valve and subjected on the other side thereof to fluid pressure in said second conduit tending to seat said third valve to oppose seating of said second valve, spring pressure urging said third valve to seated position and adjustable to predetermine the preslsure range at which said second valve will be seat to the pressure at the supply port and on the low pressure side of said seat to the pressure at thedischarge port, said valve having a portion thereof slidably extending into said passage and provided with a bore therein communicating with said supply port and said discharge port, a check "valve in said bore between the supply and discharge ports for blocking the return of fluid from said discharge port so proportioned with reference to the main valve as to area and spring pressure as to be seated when said main valve is unseated and unseated when said main valve is seated, said portion having an abutment thereon and a spring acting between said abutment and said check valve urging said check valve to seated position, a spring on the low pressure side of said seat urging said main valve to seated position, a second conduit from said passage to supply fluid from said discharge port to said main valve, a second valve in said second conduit arranged to be normally unseated and :subjected on one side thereof to the iiuid pressure in said second conduit tending to seat the same to close said second conduit to cut oifthe fluid from said discharge port to said main valve,

a vent conduit fromvsaid second conduit to said -return port to drain fluid from said second conduit upon seating of said second valve to create a differential pressure across said main valve to unseat the same in response to the said pressure at the supply port which acts thereon, a third valve for controlling said vent conduit arranged to be normally'seated and engaged on one side thereof by said second valve and unseated thereby upon the seating said second conduit tending to seat said third valve to oppose seating of said second valve, spring pressure urging said third valve to seated position and adjustable to predetermine the pressure range at which said second valve kwill be sure at the discharge port tending to seat said valve, a check valve between the supply and discharge ports for blocking the return of fluid from said discharge port so proportioned with reference to the main valve as to area and spring pressure as to be unseated when said main valve is seated and seated when said main valve is unseated, a conduit in said body for supplying fluid from said discharge port to said main valve,

4a vent conduit from said conduit to said low pressure port, a valve unit in said conduit including a sleeve provided with passages therein communicating with said discharge port, main valve and said vent conduit, a second valve in said unit arranged to be normally unseated and subjected on one side thereof to the fluid presof said second valve and subjected on the other side to fluid pressure in sure in said conduit tending toseat said second valve to close said passages to cut olf fluid from said discharge port to said main valve, a ball valve in said unit arranged to be normally seated to control the said vent conduit and subjected on one side thereof to the fluid pressure in said conduit tending to seat the same and engaged on the other side thereof by said second valve to be unseated thereby upon the seating vof said second valve to drain fluid in said conduit from said main valve to create a dierential pressure lacross the main valve to unseat the same in response to the said pressure at the supply port which acts thereon, and a springlurging said ball valve to seated position land oppose seating of said second valve and adjustable to predetermine the pressure range at whichl said second valve will be seated or unseated.

7.v In an unloading valve, a supply port, a return port, a conduit between said ports providing a main valve seat therealong, a discharge port, a second conduit between said supply port and discharge port providing a second valve seat therealong, a member having closure for said main valve seat andv presenting a diameter greater than the diameter of said main valve seat on the return port side of the seat and subjected to the discharge port pressure urging the member to cause the main valve to seat, and said member having a second closure for said second valve seat and presenting a diameter greater than the diameter of said second valve seat on the discharge side of the sea't and subjected to the discharge port pressure urging the member to the second valve seat 'when in engagement therewith, a spring urging said member to normally engage the main valve seat and open the sec'- ond valve seat, second valve means for control-v ling the pressure at the discharge port acting on the return portside of said member for creating a differential pressure condition across said member to unseat the same in response to the pressure at the discharge port acting on said member on the return port side thereof and seating said second closure on said second valve seat, whereby the difference in diameter of the second valve seat and the greater diameter on the discharge port side thereof is subtracted from the area subjected to the supply port' pressure.

8. In an unloading valve, a supply port, a discharge port and a return port, a main valve normally seated to close communication between said supply port and returnport and subjected on thelow pressure side thereof to the pressure at the discharge port tending toseat said valve `and subjected at the other side thereof tothe 'pressure at A'the supply port tending to' unseat 'said valve, a spring'urging said valve to seated position, said valve having additional opposite surfafce area-s thereon exposed to the pressures'at the supply port and discharge port in a balanced condition when said main valve is seated, second valve means for controlling the pressure at the discharge port acting on the said one side of said main valve for creating a differential pressure condition across said main valve to unseat the same in response to the pressure at the supiply port, and other valve means for shutting 01T the pressure at the supply port acting on one of said opposite areas upon the unseatino of said main valve whereby the pressure at the discharge port will act on said other of said opposite areas of the main valve to maintain the same unseated to be opposed only by the pressure of said spring.

9. In an unloading valve, a supply port, a discharge port and a return port, a main valve normally seated to close communication between said supply port and return port and having a, bore therethrough for the passage of fluid from said supply port to said discharge port, a check valve for blocking the return of fluid from said discharge port through said bore and arranged to be unseated when said main valve is seated and seated when said main valve is unseated, said main valve being subjected on the low pressure side thereof to the pressure at the discharge port tending to seat said valve and subjected on the high pressure side thereof to the pressure at the discharge port tending to seat said valve and subjected on the high pressure side thereof to the pressure at the supply port tending to unseat said valve, a spring urging said valve to seated position, said valve having additional opposite surface areas there on exposed to the pressures at the supply port and discharge port in a balanced condition when said main valve is seated, second valve means for controlling the pressure at the discharge port acting on the said one side of said main valve for creating a dierential pressure condition across saidmain valve to unseat the same in response to the pressure at the supply port, and other valve means for shutting o1? the pressure at the supply port acting on one of said areas upon the unseating of said mainvalve whereby the pressure at the discharge port will act on said other of said areas on the main valve to maintain the same unseated and to be opposed only by the pressure of said spring.

10. In an unloading valve, a supply port, a discharge port and a return port, a main valve normally seated to close communication between said supply port and return port and subjected on one side thereof to the pressure at the supply yport tending to unseat said valve and subjected on the other side thereof tothe pressure at the discharge port tending to seat said valve, a second valve for controlling the pressure at the Adischarge port acting on the said main valve, said second valve being subjected on one side to the pressure kat the discharge port tending to seat said second valve to cut off said pressure from said discharge port which acts on the said main valve, avent conduit for draining upon the seating of said second valve the pressure at said discharge port acting on the said main valve for creating a differential pressure condition thereacross to unseat the same in response to pressure at the vsupply port, a third valve for controlling said vent conduit arranged to be normally seated and subjected on one side to pressure at the discharge port tending to seat the same and engaged on the other side thereof by vsaid second valve to be lilil unseated thereby upon seating of said second valve and a spring supplementing the said fluid pressure acting on said third valve to oppose closing of said second valve whereby upon unseating of said third valve said pressure at the discharge port tending to seat said second valve will be opposed only by the pressure of said spring.

11. In an unloading valve, a supply port, a discharge port and a return port, a main valve normally seated to close communication between said supply port and return port and subjected on the high pressure side thereof to the pressure at `the supply port tending to unseat said valve and subjected on the low pressure side thereof to the pressure at the discharge port vtending to seat said valve, means including a secondV valve for'controlling the said fluid pressure tending to vseat said valve, a conduit to each side of said second valve'for the flow of fluid under pressure therethrough, said second valve ccntrolling'said conduit and subjected onY one side thereof to pressure in said conduit -tending to move saidsecond valve to shut of 'the fiow of fluid through said conduit, a vent conduit from said conduit for draining the same upon the seating of said second valve, a third valve for controlling saidv vent conduit arranged to be normally seated andsubjected on one side to the pressurey in said conduit tending to seat said third valve and engaged on the other side thereofbysaid second'valve to Vbe unseated thereby upon seating of said' second valve and a spring supplementing the said pressure acting `on said third valve to oppose closing said second valve, said fluid pressure acting on said second valve tending to seat the same will be opposed only by the pressure of said spring.

ROBERT STEVENSON.

References'Cited in the ie of this patent Vorthe OriginaI'patenIt UNITED STATES PATENTS Number Name p Date 2,091,596 Kuppel Aug. 3l, 1937 2,188,463 v Mercier Jan. 30, 1940 2,241,665 Herman May 13, 1941 2,264,375 Hill Dec. 2, 1941 2,279,571 Kane Apr. 14, 1941 2,312,877 Campbell Mar. 2, 1943 2,327,942 Thoresen Aug. 24, 1943 2,404,102 Schultz July 16, 1946 2,410,751 Schultz Nov. 5, 1946 2,447,820 Schultzl Aug. 24, 1948 2,545,712 Stevenson Mar. 20, 1951 FOREIGN PATENTS Number Country Date 8,799 Great Britain May 3, 1895 267,978 Great Britain June 23, 192'? 587,769 Great Britain Aug. 31. 1932