CA2109371C - Variable load control valve device - Google Patents

Abstract

A diaphragm-type of variable load control valve device having a diaphragm piston assembly for effectively providing pressurized fluid to the brake cylinders of a railway vehicle in accordance with the brake demand established by a vehicle operator and at a pressure level in conformance with the load condition of the vehicle.

Description

(Case No. 8728) ~109371 VARIABLE LOAD CONTROL VALVE DEVICE

FIELD OF THE lNv~N~l~loN
This invention relates to a changeable variable load control valve and more particularly to a ~i~phragm-type of variable load conL~ol valve device which functions to limit maximum value of air pressure that is directed to the brake cylinders in proportion to the ratio of the air spring pressure and brake cylinder pressure in a railway vehicle.
BACKGROUND OF THE lNV~ ON
It is well known to those skilled in the art that overbraklng and ensuing wheel lockup and wheel sliding on lightly loaded rapid and/or mass transit vehicles must be avoided since flat spots and damage to the wheels may occur during the braking o~ pa~spn~er trains. On heavily loaded railway vehicles there is the possibility that underbraking conditions may result in longer braking distAnces which may cause a railway train to overrun its normal stopping point at a station or a block section.
In order to avoid an overbraking and underbraking ao condition, it is common practice to employ a standard variable load control valve device such as shown and disclosed in U.S. Patents Nos. 3,460,872;
3,504,698; 3,517,971: 3,583,772, and 4,453,779. However, these previous varlable load control valves which are used in existing brake equipment generally consist o~ a .. ;.::.

~ ~09~i71 steppe~ or graduated piston to obtain brake cylinder p~as~uLe in proportion to the air spring pressure which COL~e~"J~-~C to the load on the railway vehicle. The piston member includes dynamic O-ring seals that move S within a cylindrical bl-chin~ which is properly dimensioned to p~cven~ air leakage between the air spring pLes~uLe chamber and brake cylinder pressure chamber.
However, it has been found that the break-away friction characteristics associated with the dynamic O-ring seals can cause a relatively large variation in the o~u~ ~;
ee~-~re particularly when the valve has been idle or ;~
~o~,e~ated ~or a long period of time, such as, an overnight lay~v6 Even th9ugh the O-rings are thorougl.ly lubricated during the initial assembly of the valve, the lubricant is eventually dissipated or ~ rsed during the s-~hsequent operation of the valve so that the amount Or static friction is dramatically lncrea~ed. Further, it will be appreciated that the brake cutorf ~eE~U1e i~ a function of the ratio of the e~ective yle-3~lres that are supplied to the upper and lower surface areas of the graduated piston of the variable load corl~Lol valve. Since various transit YLV~ ie~ have difrerent brake and load characteristics, it i~ .~eoe~Ary to provide a multitude of different pres~ure ratios be~een the air spring pressure and the brake cylinder pressure. However, ln any given stepped ~10937i , . . .

piston type of variable load control valve, the pressure ratio is fixed and can only be varied or changed by substituting a different size of graduated piston, o-rings and bllchings and, in some cases, a different intermediate filling member or casing to accommodate the different-size hllch;ngs. Thus, it will be appreciated ~ -that a relatively large number of different parts must be ~ -~
kept in inventory to e,.D~e that the variable load valve ~-devices are capable of being adapted to fill the braking requirements of the various transit authorities.
Further, it will be noted that the close manufacturing and mach~n~ng tolerances required by the different ~tspp6~ piAton~ and the coopeLatively associated b~l~h~n~s are e~le~Aive to machine and manu~acture.
SUMMA~Y ~D OBJ~TS OF TPT~ lNVL.. ~lON
Accordingly, it iB an ob~ect o~ this invention to provide a new and improved variable load valve device.
Another ob~ect of thiA invention iB to provide novel ~ m-type o~ variable load control valve for railway vehicleA.
A ~urther ob~ect o~ this invention is to provide a unique variable load aGr.L~ol valve device employing a pair o~ d~Arhragm memberA for establi~htng a maximum pre~sure value which i~ a function o~ the ratio of the e~ective alr ~prlng pre~sure area and o~ the ef~ective brake cyllnder p~e~lre area.

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. ' Still another object of this invention is to provide a novel d;Arhragm-type of variable load control valve wherein the ratio of the pressure area on a first ;~
~Arhragm and a ~econ~ rhragm may be modified by varying the diameters of a washer member and a central open1ng of a spacer member.
Still a further object of this invention is to .
., provide a ~1Aphragm-type of a variable load control valve device comprising, an upper casing section, an intermediate casing section, and a lower casing section, a ~upply chamber and a delivsry chamber located within the upper casing section, a release and check valve located within the supply chamber, a piston diaphragm assembly ~npo8e~ in the intermediate casing section, the piston ~lArhragm assembly including an upper flexible ~Arhragm having its inner periphery clamped between one washer member and a piston stem which is connected to a piston member and having it~ outer periphery clamped bat.~ean the upper cA~n~ section and the intermediate ca~ing ~ection, the pi~ton ~lArhragm assembly including a lower ~lexible ~Aphragm having its inner periphery clamped be~ en another washer and a shoulder portion of the piston member and having its outer periphery clamped be~ the lntermediate ca~ing ~ection and the lower ca~ing ~ection, a delivery control chamber located be~een the underside o~ the upper casing section and the ;.:

~ "

~ " ".;, ' 210937 1 upper side of the upper flexible diaphragm, a load CGl~rol Çh~ ~?r located in the lower casing chamber below said lower flexible diaphragm whereby fluid under pressure is col.veyed from the supply chamber to the ;~
5 delivery chr cr, and fluid under pressure in the delivery Çh~ --r is limited to a maximum value in accordance with the pressure in the load control chamber.
Yet another object of this invention is to provide an improved ~iArhragm-type of variable load control valve which is economical in cost, simple in design, efficient in service, effective in operation, reliable in use, durable in service, convenient to install, and practical to maintain.
~ r~,loN OF THE DRAWING
The above ob~ects and other attendant features and advantages will be more readily appreciated as the present ir.vention becomes better understood by reference to the ~ollowing detailed description when considered in con~unction with the accompanying drawing in which the single Figure is a schematic elevational view, mostly in section, o~ a ~aphragm-type of valve load control valve device embodying the present invention.
D~AIT~n DES~ ON OF T~ lNv~ lQN
Referring to the single Figure of the drawing, there 1~ shown a variable load valve 1 which may be used in the braklng ~yatem o~ a railway vehicle. The variable load -' ~10937 1 co~ ol valve device 1 includes three housing portions, namely, an upper casing section 2, an intermediate casing section 3, and a lower casing section 4. -;
It will be seen that a supply chamber 8 and a delivery chamber 9 are formed in the upper housing ~ ~-portion 2. A check or cut-off and release valve assembly 10 is physically ~1r~o~e~1 within the upper casing section 2 for con~olling fluid communication beL~een the supply chamber 8 and the delivery chamber 9 via pAcsageway 6 having an An~ ar valve seat 7 ~ur~ l;ng the end ~ -open1ng into the supply chamber 8. The supply chamber 8 1~ co~ ted to a ~ultable so~ce of air pressure, such as, a vehl¢le storage ~e3c~0ir (not shown) via port 11 and plpe 12, whlle the dellvery chamber 9 ls connected to lS veh~lAr brake cyl~or~ (not shown) via port 13 and plpe 14. The valve assemblage 10 includes a ~Rh1ng member lS A~ t-~ ln the top portion of the upper casing ~ection 2 in which a valve carrying member 16 is coaY~ally slidably mounted therein. The valve carrying member 16 includes a spring bla~ed An~ Ar check valve 17 located in the lower end. A relatively llght spring 18 normally urges the valve carrylng member 16 ~u..wardly toward a closed position in which the check valve 17 OC~p~4~ a ~eat-d posltion on valve ~eat 7 to cut o~
communicatlon th~ough the p~sA~eway 6. A through port l9 is formed in the valve member 17 and in the bottom of ~ . ~....

' ' ~109371 the carrying member 16 to provide a balance state of fluid p~es~ure between both sides of the check valve. A , -' release valve 20 is operably located in a release valve chamber 21 located above the check valve 17. The release valve 20 is provided in order that the unseating of the check valve 17 may be effected when the fluid pressure in the supply chamber 8 is either re~uce~ or released for nullifying an existing brake application condition. When the check valve 17 i8 in its seated position on the valve seat 7, a bAlAn~e state exists since the delivery ~e~ re acts on both sides thereof, and any valve change o~ the ~upply p~ re, particularly a ~assu~~ reduction in the ~upply chamber 8 would be ineffective on the check valve 17 unle~s ~ome means i8 provided for relieving the upper 6ide of the chec~ valve of the delivery pressur6 acting the~eon 80 that the pressure acting on the underside thereof is ,~ '~red effective for unseating the ¢heck valve 17.
As shown, the upper end of the bl~ch~ng member 15 is provided with an ops~ng 22 which is i~u~oln~led by a valve seat 23. The relea~e valve 20 i8 ,urged toward a ,~
~eated or retAin~nq position on the valve seat 23 by a ~' helical compre~sion ~pring 24 and the supply pressure ~cting on the upper oide thereo~. The top portion of the 2S bl~lng ~pring 24 1- di~po~ed wlthln a central open1ng ~ormed in protective cover member 2a which i~ suitably :
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bolted to the top end of the upper casing section 2. As viewed in the drawing, the underside of the release valve 20 is in communication with and is subject by way of op~n;ng 22 to delivery fluid pressure acting on the upper side of the check valve 17. The upper side of the release valve is in communication with and is subject to supply fluid pressure in chamber 8 by way of a port 2s which co~ e~i',s the supply chamber 8 to the peripheral space of the release valve chamber 21 in which the :-release valve 20 is loosely li~poseA. Thus, as long as the combined forces of the supply fluid pressure and the -.
,s,pring 24 acting on the upper side of the release valve 20 are greater than that o~ the delivery fluid pressure acting on the underside thereof', the release valve 20 will be held in its seated position on the valve seat 23.
Now when the supply air yfLes~e in chamber 8 is r~e~ ce~
or released due to the initiation of a braXe reduction, the delivery yLcE-~re in chamber 9 acting on the underside of the release valve 20 will overcome the ~orces on the upper side of the release valve 20 so that the release valve 20 becomes op~n~ by being unseated ~ ~:
f'rom the valve seat 23. Thus, the checX valve 17 also becomes unseated by the h~gher pressure acting on the underside thereof' to thereby cause a reduction of the delivery f'lu1d ,~rC,~s~re ln f~f~o}ffGrLflon to the reduction in the supply ~luld yle~E~lre.

As shown in the single Figure of the drawing, a hollow piston stem or plunger 26 extends coaxially from a piston member 27 while the upper end 29 of the piston stem or plunger 26 makes abutting contact with the underside of the check valve member 17 to normally maintain the check valve in its unseated position from seat 7 so that a communication fluid path through pA~Ag u~y 6 is normally op~ne~. It will be seen that the piston stem 26 p~s~s through op~n~ng 6 and also through open~n~ 31 formed in the lower wall 30 of the upper casing section 2 and into delivery control chamber 32. It will be observed that the piston member 27 which 1~ constru¢ted of a self-lubrication polymer material is u-r~pel~ed and ~posed within the intermediate casing section 3 by a pair o~ flat annular rubber diaphragms 33 and 34. ~he inner peripheral portion of the upper resilient ~lArhragm 33 iB clamped beL~c0n the top of an inner Annl-lAr w~h~r 3S and an annular collar 36 which is integral with the plston stem 26. In practice, the lower end 28 of the piston stem 26 is screw threaded into the top of the movable piston member 27. It will be noted that outer peripheral portion of the flat resilient ~:
~t~rhragm 33 is clamped be~een the upper and ;~
lntermediate ca~ing ~eotions 2 and 3. As shown in the ~ingle Figure of the drawlng, an outer annular ~p~cer member 39 is disposed between the underside o~ the top 9 , ~.

~' ~1û9~71 diaphragm 33 and a recessed portion 38 formed in the top of the intermediate casing section 3. As shown, the inner peripheral portion of the lower resilient ~i~phragm 34 is clamped between the top of an annular washer 37 and the bottom of an enlarged shoulder portion 40 by a lower piston stem 41 which is screw threaded into the bottom of the reciprocable piston 27. It will be seen that an outer annular spAcçr member 42 is A~posed between top side of the lower resilient Ai Aphragm 34 and a reces~e~
portion 43 formed in the bottom of the intermediate casing section 3.
A lower pressure area is sub~ect to a load control p~a~ re in a spring chamber 44 formed in the lower casing section 4. ~he chamber 44 i8 charged with the air spring pressure via pA~s~r,~ys 46, 47, and 48 formed in the lower, intermediate and upper casing sections 4, 3, and 2, ~a~ye~Lively. The pAcsAgeway 48 iB connected to ~;:
the air sprlngs (not shown) via a pipe 49. The level or degree of ovnL-~l pressure or air spring pressure in the ;:
spring chamber 44 i5 Aep~ndent upon and reflects the existing load condition of the railway vehicle. Thus, the amount of air pressure in chamber 44 is a ~unction of the load carried by a vehicle which is calibrated from an empty to a ~ully loaded condltion. A ~lrst helical ¢ompre~lon or bia~lng ~pring 50 18 dlspo~ed ln the alr ~.
sprlng chamber 44 and urges the dlaphragm piston 27 , " ~,~

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: ~ ' ' ', ," ' : . ~ , ' . ~' " ' .' ' -~-'" 2109371 upwardly toward an open supply position as will be .
described hereinafter. The biasing spring 50 is compressed be~een an upper spring seat 51 and a lower spring seat 52. The upper spring seat 51 rests against the lower end of the piston stem 41, and the lower spring seat 52 is fixed against rotational movement by a pair of diametrically oppose~ tabs 53 and ribs 54. Thus, the axial position of the lower spring rest 52 may be moved up or down by ad~usting screw 55 which is s~Lewed into a threaded bore in the spring seat 52. Hence, the height of spring 50 may be ad~usted for varying the compressive force, and after being suitably ad~usted, the adjusting ~crew 55 may be locked against inadvertent rotation by lock nut 56. An auxiliary or second compression spring 57 i8 caged in a rece6s 58 formed coAY~lly in an auxiliary piston 59 which is reciprocally disposed in a bore 60 formed in ad~usting screw 55 and recess 61 formed in s¢rew member 55. .. ~
In describing the operation of the present variable .;
load con~Lol valve device 1, it will be assumed that the ::
supply reservoir is charged with a fluid pressure at a normal operating value and that the spring air chamber 44 is being supplied with a pressure which is representative o~ the exieting veh~c~lA~ load. Thus, it will be :~
2S a~pL~oiated that until ~u¢h time as the engineer inltiatee a brake application, the supply chA~her 8 and ,' ' ' ' . ~; , . '., . , ','., ' ~ '' ' ~. ' . ' . ' , '. ' ,' ' , :' ."' ~109371 .

the delivery chamber 9 and the control pressure chamber .
32 are void of fluid pressure so that the piston 27 and :-~i~phragms 33 and 34 are effectively under the influence of the compression spring 50 and the air spring pressure in COI~ ol chamber 44 to assume a normal or supply position as shown and in which the check valve 17 is in its unseated position and the release valve 20 is in its seated position.
Now when the engineer or trainman initiates a service brake application, the associated control devices cause operating fluid pressure, the level of which is ; :~
~epen~nt upon the degree of brake application requested by the operator, to be 6upplied to the supply chamber 8 vla pipe 12 and port 11. The supply pressure then rlows through the open check valve 17 through pa~A~eway 6 to ~ .
the delivery chamber 9. The fluid pressure in the delivery chamber 9, in turn, flows through port 13 and pipe 14 to the brake ¢ylinder~ for instituting a brake application on the railway vehicle. At the same time, ~luid pressure in the delivery chamber 9 flows through ~
the intervening p~R~ag e~_y 31 in wall 30 and into the ~:.
chamber 32 and acts on the pressure area PAS which is .:
e~fectively and primarily determined by the bore diameter o~ the 3p~Gsr 39. It will be also seen that the ~luid ~: i pre~ure ln air ~pring chamber 44 act~ on the pressure area PAA which is e~fectively and primarily determined by ' . .~ . ~.. ..

:. . :

~109371 the bore diameter of spacer 42. In viewing the single Figure of the drawing, it will be seen that the pressure area PAS is somewhat greater than the pressure area PAA.
In the present instance, the ratio of the two surface areas may be, for example, approximately 2:1. As will be described hereinafter, the pressure area ratio may be varied or ch~n~ed as the situation warrants for various brake applications on different types of vehicles. For example, if the degree of brake application by the train operator i8 of such a low level that the pressure of the operating fluid acting on the pressure area PAS is insu~icient for overcoming the opposing forces of the b~aelng epring 50 and the air spring pressure in the chamber 44 acting on the pressure area PAA, then the positions of the res~e~Live ~Arhragms 33, 34, washer 35, piston 27, and piston ~tem 25, as well as the check valve 17, will remain ~~n~h~nqed.
er, if the operator now either initiates a new ~ervice brake application or effects an increase of the existing low level service brake application to the ~ ~
extent that the degree of operating air pressure now ~ ~' active on the pressure area PAS is su~icient to overcome the opposinq ~orces acting on the pressure area PAA, then the ~1Aphraqm3: 33, 34, washer 35, piston 27, and piston etem 25, ae well ae the check valve 17, are moved do~nwardly out o~ the normal poeition to a ~losed or non-supply position. Under this condition, the biasing .
,, , ", ,,: , j:, . . .. . . .....

210~371 spring 18 moves the check valve 17 downwardly against the seat 7 to cause the check valve 7 to assume its closed or cut-off position. Thus, the flow of operating fluid under pressure to the delivery chamber 9 and to the brake cylinders is cut off at the given level determined by the compression setting of the spring 50 and the degree of air spring pressure in the chamber 44, even though the operator may attempt to further increase the brake application by effecting an additional increase of fluid -~
pressure in the supply chamber 8. Once the check valve 17 is seated, the forces on both sides of the diaphragms 33 and 34 are balanced and the check valve 17 is retaine~
in lts retained position until such time that the supply pressure in chamber 21 acting on the upper side of the release valve 20 is exhausted or vented to atmosphere.
Now when the operator effects a brake reduction or relea~e of the brake application and the supply pressure is decreased sufficiently, the delivery pressure on the ;~
underside o~ the release valve 20 causes it to become unseated. Thus, the service brake operations, the maximum limit of the fluld pressure deliverable to the brake cylinders, namely, the pressure at which the cutoff o~u. is determined by the existing load condition of the vehiale, that lo the degree o~ air spring pressure in the alr spring chamber 44. Accordingly, the force o~ the air spring pressure in chamber 44 plus the force of the . . , , ~- ~, .. , , ,:
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' , ;~ ', , ', ,; . , .

compression spring 50 is the amount of force that must be overcome by the operating fluid pressure which is in the delivery chamber 9.
It will be appreciated that all brake applications whether service or emergency are released when the operator in an applo~Liate manner causes the actuation of a suitable co~ ol valve device to effect the release of the fluid pressure in the supply chamber 8. Thus, when a brake reduction i8 initiated by releasing the fluid pressure in the supply chamber 8, the upper side of the release valve 20 ia relieved of the supply fluid pressure ~o that the ~luld p~s~ re on the under side thereof is e~e¢tive in ~ ing the release valve 20 from seat 23.
The delivery pressure acting on the upper side if the check valve 17 i8 permitted to escape past the unseated release valve 20 ~o that the delivery pressure now acting only on the under slde o~ the check valve 17 causes it to become unseated. It will be seen that with the check valve 17 unseated, the fluid pressure acting on the ~e~ e area 32 o~ the flat diaphragm 33 i5 relieved so that the various parts are returned to their normal position by the spring 50, and the air spring pressure in chamber 44 to completely unseat the check valve 17.
Thu~, the ~luid pres~ure ~rom the brake cylinders may readily ~low through pipe 14, port 13, delivery chamber 9, through pa~sageuay 6, past the unseated check valve , ' ' . ' : , ' : "' :
'~109371 --::.'' 17, through chamber 8, through port 11 to pipe 12 and to an atmospheric port in the control device (not shown).
It will be appreciated that, if an overshoot condition oc~iuLs, the air in the chamber 8 will flow into chamber 9 and chamber 32 located above the diaphragm 33. ~ :~
The force of the overshoot air pressure will move the piston and ~lArhragm assembly rapidly downwardly so that the piston stem 26 pulls away from the valve 17.
Accordingly, air under pressure in the chamber 9 will then flow through the pAq~Ag2way 62 in the piston stem 26, pA~age~ay 63 in the piston 27, passageway 64 in the intermediate a_~ing section, and will be vented to atmc~phsre at port EX until the overshoot condition is a~,e_Led.
As previously mentioned, the presently described variable load avnL.ol device 1 is a differential type of p~e--~re operating device in which the ef~ective surface area FAS may be readlly chAng0d by ~imply removing and r~plac~ng the waeher 35 and the ~pAcer 39. In order to cha~,~ the ratio o~ the pressure area PAS relative to the p~e~u~a area PAA, it is merely nece~sary to change out the upper washer and ~FAcsr members. To increase the ~r~ lre ratio, the outside diameter of the washer 35 and the inner dlameter o~ the clraular hole ln the spacer 30 are lncreased. Corl~6~ely, to decrease the pressure ratio, the diameters of the washer 35 and the circular i. , ~, : , , - . ~ . ... . . .

"2109371 hole in the spAcer 39 are decreased. Thus, the ratio of the pressure areas may be readily selected and/or changed ~-~
to compensate for various supply and air spring pressures as well as for varying compressive forces of various springs.
The use of the two flat polyurethane ~i~phragms can ~-~
simulate the function of a steppe~ piston of variable load COII~r ol valve device and also alleviates the friction breakaway problems associated with dynamic 0-rings. It will be noted that the d;~rhragm-type of variable load control valve permits the ratio between the alr spring p~e~ re and the brake cylinder pressure to be ~c~ly and ea~ily ¢hA~ea by interchanging two simple and ~--a~e~ive com~one..~s. The use o~ a self-lubricating polymer piston member eliminates the need of ~i extrAneo~ic lubricants.
Thu~, the pl~ent invention has been described insuch ~ull, clear, concise and exact terms as to enable any person skilled in the art to which it pertains to make and u~e the same, and having set ~orth the best mode contemplated o~ carrying out this invention. I state that the sub~ect matter, which I regard as being my invention, is particularly pointed out and distinctly asserted in what i~ claimed. It wlll be understood that variations, modi~lcatlons, equlvalents and substitutions for components o~ the above specifically-described : ~:'' .

~iO937i , embodiment of the invention may be made by those skilled ~-in the art without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims (15)

1. A diaphragm-type of variable load control valve device comprising, an upper casing section, an intermediate casing section, and a lower casing section, a supply chamber and a delivery chamber located within said upper casing section, a release and check valve located within said supply chamber, a piston diaphragm assembly disposed in said intermediate casing section, said piston diaphragm assembly including an upper flexible diaphragm having its inner periphery clamped between one washer member and a piston stem which is connected to a piston member and having its outer periphery clamped between said upper casing section and said intermediate casing section, said piston diaphragm assembly including a lower flexible diaphragm having its inner periphery clamped between another washer and a shoulder portion of said piston member and having its outer periphery clamped between said intermediate casing section and said lower casing section, a delivery control chamber located between the under side of said upper casing section and the upper side of said upper flexible diaphragm, a load control chamber located in said lower casing chamber below said lower flexible diaphragm whereby fluid under pressure is conveyed from said supply chamber to said delivery chamber and fluid under pressure in said delivery chamber is limited to a maximum value in accordance with the pressure in said load control chamber.

2. The diaphragm-type of variable load control valve as defined in claim 1, wherein said piston member is constructed of a self-lubricating polymer material.

3. The diaphragm-type of variable load control valve as defined in claim 1, wherein a first annular spacer member is disposed in an annular recess formed in the top of said intermediate casing section.

4. The diaphragm-type of variable load control valve as defined in claim 3, wherein said first annular spacer member includes a central opening for accommodating said one washer member.

5. The diaphragm-type of variable load control valve as defined in claim 4, wherein the diameter of said one washer member is substantially equal to the diameter of said central opening of said first annular spacer member for establishing a first pressure area.

6. The diaphragm-type of variable load control valve as defined in claim 1, wherein a second annular spacer member is disposed in an annular recess formed in the bottom of said intermediate casing section.

7. The diaphragm-type of variable load control valve as defined in claim 6, wherein said second annular spacer member includes a central opening for accommodating said shoulder portion of said piston member.

8. The diaphragm-type of variable load control valve as defined in claim 7, wherein the diameter of said shoulder portion of said piston is substantially equal to the diameter of said central opening of said second annular spacer member for establishing a second pressure area.

9. The diaphragm-type of variable load control valve as defined in claim 5, wherein said first pressure area is exposed to pressure supplied to said delivery control chamber when said check valve is open.

10. The diaphragm-type of variable load control valve as defined in claim 9, wherein said second pressure area is exposed to pressure supplied to said load control chamber.

11. The diaphragm-type of variable load control valve as defined in claim 1, wherein a compression biasing spring is disposed in said load control chamber.

12. The diaphragm-type of variable load control valve as defined in claim 1, wherein said piston stem is secured to said piston member and includes a remote end for engaging and unseating said check valve.

13. The diaphragm-type of variable load control valve as defined in claim 12, wherein said piston stem is a hollow member which is connectable to atmosphere to vent said delivery chamber.

14. The diaphragm-type of variable load control valve as defined in claim 1, wherein said release valve is unseated when the pressure in said supply chamber is reduced to permit the unseating of said check valve.

15. The diaphragm-type of variable load control valve as defined in claim 5, wherein said first pressure area may be varied by changing the diameters of said one washer member and said central opening of said first annular spacer member.