US3414007A

US3414007A - Load lowering valve for hydraulic hoists

Info

Publication number: US3414007A
Application number: US448919A
Authority: US
Inventors: Marco Robert F De
Original assignee: Fluid Controls Inc
Current assignee: Fluid Controls Inc
Priority date: 1965-04-19
Filing date: 1965-04-19
Publication date: 1968-12-03
Anticipated expiration: 1985-12-03

Description

Dec. 3, 1968 F. DE MARCO 3,414,007 7 I LOAD LOWERING VALVE FOR HYDRAULIC HOISTS I Filed April 19. 1965 2 Sheets-Sheet 1 INVENTOR.

05597 F flf/WARCO BY Z51 ATTORNEK Dec. 3, 1968 R. F- DE MARCO 3,414,007

LOAD LOWERING VALVE FOR HYDRAULIC HOISTS Filed April 19, 1965 2 Sheets-Sheet 2 INVENTOR.

3: AT70/P/VEK United States Patent 3,414,007 LOAD LOWERING VALVE FOR HYDRAULIC HOISTS Robert F. De Marco, Mentor, Ohio, assignor to Fluid Controls, Inc., Mentor, Ohio, a corporation of Ohio Filed Apr. 19, 1965, Ser. No. 448,919 12 Claims. (Cl. 137-493) ABSTRACT OF THE DISCLOSURE The present disclosure is directed primarily to a load lowering valve for a hydraulic hoist. A valve plug with a plurality of ports is seated on a seat area provided with a plurality of ports. The plug is yieldably rotated in the direction toward maximum registry of the ports by a torsion spring which also urges the plug toward the seating area. The structure permits a relatively free flow through the body from the inlet to the outlet, but restricts the flow from the outlet to the inlet in relation to the pressure of the fluid at the outlet side of the wall.

This invention relates to a load lowering valve for hydraulic hoists, and to the combination of a low lowering valve with the hoist of a conventional industrial lift truck.

For purposes of illustration, the lowering valve is disclosed as applied to such conventional lift trucks, its use for other purposes being apparent from the illustrative example.

It is desirable that such lift trucks be capable of lifting and lowering loads with the highest speed consistent with safety. No serious problem is presented in lifting and lowering very light loads. However, a serious problem is presented in controlling the hoist of such a truck automatically so that at optimum efficiency and with safety, it lowers loads which approach its rated capacity. This problem is due primarily to the inability of the existing hydraulic circuits to respond at the inception of lowering to the load imposed on the hoist so as to limit the lowering speed from the inception of lowering. The circuits in general use become responsive to the load imposed and operative thereby to limit the lowering speed only after a substantial downward travel of the loaded hoist during which a normally open valve, by gradually and progressively throttling the discharge of hydraulic pressure fluid from the hoisting piston and cylinder assemblage, reduces the lowering speed to that consistent with safety for the particular load. During this initial travel, the load gains an unsafe momentum and its speed is reduced so abruptly and to such a degree that the inertial forces tend to overload and overturn the truck, to damage the hoist mechanism, and to cause displacement of the load or damage thereto, thereby endangering the lives of operators.

On the other hand, efliciency requires that hoisting and lowering the empty or lightly loaded lift forks must be at very high speed, which generally requires a substantially unthrottled flow of hydraulic fluid to the hoist cylinder.

The present invention has to do with a load lowering valve which permits rapid traverse of the hoist under no load or light load conditions yet which, as the load is being applied and before the initiation of lowering, adjusts itself so as to regulate the lowering speed to the optimum speed consistent with safety for lowering the particular load.

Heretofore, attempts have been made to provide valves which are adjustable automatically for lowering at speeds commensurate with the size of the load. However, these valves are generally fully open at the inception of the load lowering operation and are adjusted for their modulating or throttling action is by the return flow of fluid 3,414,007 Patented Dec. 3, 1968 from the hoist cylinder during actual lowering. As a result, a time element is involved which makes it impossible to obtain proper modulation or throttling for adjustment of the lowering speed at the inception of the lowering operation. Consequently, the lowering of the load is substantially unresisted at the inception of lowering and, in effect, the load drops initially an appreciable distance during which the valve becomes adjusted to reduce the speed to the safe lowering speed for the truck. This initial drop quite often only comes only after the load has gained dangerous momentum.

Such prior valves also have a tendency for weaving and surging during the lowering cycle while seeking to render the lowering speed constant.

In accordance with the present invention, the lowering valve opens fully for a free flow of pressure fluid during lifting. However, during lifting operations wherein the forks are disposed under a load and the hoists operated to transfer the load to the forks, a sensing device in the valve senses the increase in the load on the forks during the lifting of the forks and before any return flow occurs, of hydraulic fluid and adjusts the valve as the load is being transferred, so that, by the time the load is fully supported on the forks and before the inception of the lowering operation, the valve is fully adjusted in response to the load itself for lowering the load at the reduced optimum safe speed. Thus the valve attains this adjusted position while the hydraulic fluid is flowing through it for lifting the hoist, it is in the adjusted position at the inception of lowering, and it remains in the adjusted position throughout the lowering operation. Consequently it eliminates sudden initial drops of the load, and also surging and Weaving resulting from modulation of the throttling effect by the return flow of hydraulic fluid.

Only after the valve has been adjusted and secured in adjusted position in response to the load to be lowered, is lowering initiate, and this, of course, is effected by opening the conventional manual lowering or return valve to permit the hydraulic fluid to flow from the hoist cylinder back to the sump or reservoir of the truck.

On the other hand, if the hoist is held static and articles are piled on the forks by extraneous means so that the load is gradually increased, the sensing device senses the increments of load and progressively sets the valve for reduced lowering speeds as the load is increased an while the fluid in the circuit between the pump and the hoisting cylinder are in static equilibrium. Again the valve is retained in its finally set position until the manual lowering valve is opened for lowering the load, or until the load is reduced.

If the load is gradually reduced by removing articles successively from the forks, the sensing device progressively sets the valve for increased lowering speeds proportional to reduction of the load.

The instant the manual lowering valve is opened, the differential in pressure on the opposite sides of the load lowering valve holds the valve firmly in its adjusted throttling position so that the proper setting for lowering is maintained.

Another advantage of the present valve is that it is simple in construction and permits self-cleansing and flushing for at least part of each cycle so that dirt and the like, commonly present in the reservoirs of such trucks, can readily be flushed out of the valve.

Specifically, the present valve is a normally open valve which closes as the load is being increased and opens as the load is being reduced, by and in relation to the weight of the load and before inception of the lowering operation.

Various objects and advantages will become apparent from the following description where reference is made to the drawings, in which:

FIG. 1 is a diagrammatic side elevation of an industrial lift truck in which the valve of the present invention is installed;

FIG. 2 is a hydraulic circuit diagram showing the various control valves and means for operating the hoist for lifting and lowering a load;

FIG. 3 is a top plan view of the load lowering control valve embodying the principles of the present invention;

FIG. 4 is an enlarged vertical sectional view through the valve, taken on the line 4-4 in FIG. 3;

FIG. 5 is a diagrammatic illustration of the valve and its load sensing device, showing one setting of the metering means of the valve by the sensing device for lowering a light load; and

FIG. 6 is a diagram similar to FIG. 5 showing another setting of the metering means by the sensing device for lowering a heavy load.

Referring to the drawings, the valve is shown in connection with an industrial lift truck 1 having the conventional counterbalanced body 2 and supporting wheels 3. This forward end of the truck is provided with an upright main mast 4 on which an extensible supplemental mast 5 is supported for vertical movement. The mast 5 carries at its lower end a hoist carriage 6 which is vertically therealong. The carriage 6 has the usual lift forks 7 extending forwardly therefrom for supporting a load L.

The masts and carriage structures are operated by suitable cables 8 threaded through the usual sheaves. The cables are operative when moved endwise under tension to lift the carrier 6 to the top of the extension mast 5, and then, upon continued endwise movement, to lift the carriage and mast 5 as a unit to the top of the main mast 4.

The cable is drawn in endwise and paid out by a suitable piston cylinder assembla-ge including a cylinder 9 and a piston 10 having a piston rod 11 connected to the cables 8. For supplying hydraulic fluid to the piston for lifting the load L, a suitable pump 12, driven by a motor 13, is provided. The pump is connected to a manual hoisting and lowering valve 14 which, in turn, is connected to the one end of the cylinder 9 by a pipe line 15. The pump has an intake line and valve 14 has a discharge line. These lines are connected to a common sump or reservoir 16. The valve 14 is operable to introduce hydraulic fluid to the cylinder 9 for moving the piston on the hoisting stroke, and to release the fluid for return to the reservoir 16 to permit the hoist to lower.

The structure thus far described is well known in the art. With this structure, the reversing valve 14, when set for return flow, permits rapid lowering of the load and the danger is ever present that a heavy load is apt to be lowered at an unsafe speed due to human error. In order to control the lowering of the load automatically, the valve 20 of the present invention is provided.

Referring to FIGS. 3-6, the present load lowering valve comprises a hollow body 21 which may be formed by two coaxial sleeves 21a and 21b in threaded engagement with each other. The body 21 has an inlet 22 at one end and an outlet 23 at the opposite end. The valve is connected in the line 15 with the inlet end connected to the pump 12 and the outlet end connected to the cylinder 9. In the body are suitable throttling means which are operable to control lowering in the manner hereinbefore described.

In the form illustrated, the throttling means comprises a combined seating and metering disc 24 which is securely held in the body by clamping its peripheral margin between the portion 21a and a sleeve 25 which at one end engages the disc 24 and at the other end engages the inner end of the sleeve 21b. A suitable sealing or O-ring 26 is provided so that the combined seating and metering disc 24 forms a partition wall across the inside of the body between the inlet and outlet. The disc 24 has passage or orifice means extending therethrough to permit the flow of hydraulic fluid from the inlet to the outlet when the valve is opened. The orifice means shown are in the form of a plurality of orifices 27 which are spaced about the axis of the disc. The angles of distribution of each two adjacent orifices are shown as different from each other two adjacent orifices so that the orifices are not uniformly distributed. These orifices are positioned so that they are fully exposed to the pressure fluid from the inlet 22.

Mounted within the body at the outlet side of the disc 24 is a metering valve member 39 which has a setting position 31 with a face complementary to that face of the disc 24 at the outlet side and which is adapted to seat firmly thereon for controlling the flow of fluid through the orifices 27 depending upon the rotated position of the valve member 30. For supporting the valve member 30 for movement to and from seating relation on the disc 24, the disc 24 is provided with a central cylindrical guide 32. The valve member 30 is provided with a central integral sleeve 33 which fits the guide 32 with operating clearance and supports the member for axial movement toward and away from the seating face of the disc 24 and for rotation about the axis of the disc 24. The member 30 preferably also has an outer peripheral flange 34 which extends axially thereof in coaxial relation to the sleeve 33.

In order to hold yieldably the valve member 30 against the disc 24, a combined compression and torsion spring 35 is provided. One end 35a. of the spring 35 is received in a slot 36 in the peripheral flange 34 of the member 30. The other end 35b is received in a socket 37 formed in the body portion or sleeve 21b. The sleeve 25 performs an additional function of assuring that the interlocked end 35]) of the spring 35 is not pulled out of its socket 37, but is held tightly therein. The spring 35 acts not only as a compression spring to hold the member 30 lightly seated when there is no fluid pressure differential at opposite sides of the member 30, but also acts as a torsion spring which urges the member 30 to rotate in one direction. The torque exerted by the spring on the member can be varied or adjusted by changing the size of the spring. The member 30 has orifice means provided by orifices 39 therein. The orifices 39 likewise are spaced apart different distances angularly, relative to each other, about the axis of rotation of the member and preferably at a different angular spacing than the orifices 27 of the disc 24, so that as the member rotates to different relative positions relative to the disc, the total amount of orifice area through the valve is increased or decreased incrementally with a Vernier type of adjustment, so that the return flow of fluid can be very precisely adjusted to the load by infinitely small increments of change. If desired, however, the orifices of both members may be positioned so that they can be fully aligned within each other concurrently.

Prom the structure thus far described, it is apparent that upon opening the manual valve 14, fluid is admitted through the inlet 22 and unseats the valve member 30 thereby permitting a relatively free flow of hydraulic fluid through the valve from the inlet to the outlet. On the other hand, when the manual valve 14 is closed, the pressure at the inlet and outlet of the lowering valve 20 balances when the manual valve 14 is turned in the opposite direction for connecting the cylinder for return flow of fluid to the reservoir, the member 30 seats, and the amount of return flow from the outlet to the inlet is determined by the total of the aligned areas of the

orifices

27 and 39 of the disc 24 and member 30, respectively. Thus, the metering is determined by the rotated position of the member 30. The tourque of the spring 35 is such as to yieldably hold the member lightly seated on the disc 24 so that the member can be removed therefrom readily and can be rotated while seated or unseated with a predetermined minimum of fluid pressure, depending on the torsional force of the spring 35. However, when the member 30 returns to the seat and a substantial positive differential in fluid presure exists at the outlet side of the member, this differential seats member firmly enough to frictionally lock it against rotation by the spring out of the position in which it had been set at the time of seating.

At this point is should be noted that the Spring 35 need only be a torsion spring, inasmuch as gravity also is a means for urging the member yieldably against its seat. However, since a. spring is to be provided for torsion, it can be selected to perform both of these separate distinct functions, thus providing a means for yieldably seating the member and also a means for rotating the member.

As mentioned heretofore, it is desirable that the rotational setting of the member 30 for metering the return flow be accomplished before the intiation of return flow or load lowering operation. For this purpose, a sensing device responsive to the pressure of the fluid in the body is provided and is operative by the pressure fluid to rotate the member against the resistance of the spring 35. This device comprises a cylinder 40 in which a piston 41 is reciprocable. The piston is connected to the member 30 so that when pressure fluid is applied to the piston, the piston rotates the member in opposition to the spring 35. This connection may be provided by a flexible cable 42 connected at one end to one end of the piston 41 and connected at the other end to the member 30. The connection is shown as made by looping a part of the cable around the sleeve portion 33. The cable 42 extends radially outward through a notch or aperture and is wrapped about the outer face of the flange 33 which acts as a drum. Thus, as the fluid pressure increases on the piston 41, the piston 41 rotates the member 30 counterclockwise in FIG. 3. The spring 35, however, urges the member 30 to return in the clockwise direction. The spring 35 is arranged so that it normally yieldably holds the member in the maximum open position wherein the maximum area of registry of the

orifices

27 and 39 is provided, as illustrated in FIG. 5. Thus a relatively free flow of hydraulic fluid from the inlet to the outlet is obtained by unseating of the member 30 by the fluid. This is true throughout the range from no-load to full-load. At no-load, there is a somewhat restricted return flow when the member is seated, but adequate for rapid lowering. However, as

fluid pressure is being built up in the cylinder for hoisting a load, the pressure builds up in the body and operates the piston 41, and rotates the member 30 in the direction for increased throttling. The greater the pressure, the less becomes the total orifice area in registry, thus increasingly restricting the return flow. The adjustment due to the piston 41 is being continuously effected as changes in pressure in the body occur; for example during hoisting when the member 30 is unseated, and when the load is suspended in static condition as a result of closing the manual valve 14, so that the pressure is equalized at oppo-. site sides of the member 30 and the member 30 is held lightly seated by the spring 35. When the load has been hoisted the manual valve 14 is turned to stop position. When the valve 14 is moved to the reversing position, the load starts lowering. However, the valve member 30 already has been set to position for the optimum safe lowering speed prior to inception of lowering and consequently no sudden drop of the load can occur.

In operation, assume that a load is on a pallet on the floor and is to be hoisted. The forks are run beneath the load and pressure fluid is admitted to the hoist cylinder manually by opening the manual valve 14 for hoisting. Immediately, the pressure fluid starts operating the hoist cylinder. As soon as the forks engage the load and starts hoisting, the pressure in the circuit builds up in proportion to the load being transferred to the forks. During this increase in pressure, the piston 41 progressively rotates the valve member 30 to metering positions in which the effective aligned area of the

orifices

27 and 39 is reduced. Meanwhile there is a free flow of pressure fluid from the inlet to the outlet during this adjusting operation, due to unseating of the valve member 30. When the load is fully transferred to the forks, the lowering adjustment is com- 6 plete. When the load has been hoisted to the height desired, the manual stop and reversing valve 14 is moved to stop position. The pressure balances on each side of the valve member 30 and the valve plug is seated lightly by the spring 35. The load is then transported to the location at which it is to be lowered. The manual valve 14 is set for return flow for lowering the load. As soon as this occurs, the pressure at the inlet side of the member 30 is reduced, due to bleeding off of oil to the reservoir 16. Hence, instantly a positive differential of pressure occurs at the outlet. This pressure augments the force of the spring 35 and seats the valve member 30 sufficiently firmly so that even without pressure on the piston 41, the spring 35 cannot rotate the member 30 against the frictional seating resistance. Consequently, the: plug retains its set position for lowering. If the load is removed from the forks, the pressure at the opposite sides of the member 30 tends to balance, and in such condition the spring is strong enough to rotate the member to its normal open position, whereupon the empty forks can lower rapidly.

On the other hand, assume that a load is on an elevated rack and is to be removed and lowered. The forks are raised by opening the valve 14 which unseats the member 30 to permit a relatively free flow of lflllld to the cylinder assembly 9. This raises the forks rapidly to a position to accept the load. With the forks beneath the load, the cylinder 9 continues to operate, gradually transferring the load from the rack onto the forks. However, as it does so the pressure in the body of the valve necessarily increases commensurate with the load, and as the forks rise so that the load is finally fully transferred to the forks, the piston 41 is operated to set the valve member 30 against the force of the spring 35 and reduce the effective aligned areas of the

orifices

27 and 39. When the load is fully on the forks, the member 30 has already been rotated to the proper position for lowering the particular load. Here again, when the valve 14 is turned to stop position, the pressure remains unchanged, holding the member 30 set in throttling position. Upon reversing the valve 14 for return .flow, the pressure at the inlet is suddenly reduced, and the pressure at the outlet, imposed by the load, seats the member 30 more firmly and holds it frictionally in the set position. As soon as the load is lowered and transferred so that the forks are relieved therefrom, the pressure on both sides of the member 36 equalize and the piston 41 can no longer resist rotation of the member 30 by the spring 35, and the spring then returns the member to the maximum registering position of the orifices. If the hoist is raised, the valve 14 closed, and the load is applied by manually placing additional packages on the forks, the pressure at the outlet side of the member 30 increases, operates the piston, and continuously sets the member for lowering as the load increases.

Because of the combined check and metering valve action of the member 30, foreign matter on the seat or between the member and seat is flushed away by the hydraulic fluid when the hydraulic fluid flows in the hoisting direction.

It has been found that with the present structure, the range of lowering speed from 146 feet per minute when lightly loaded to 34 feet per minute under full-load may be obtained with a single valve. A greater variation, of course, can be obtained by increasing the number of the valves in parallel, or the size, port arrangement, and spring. Heretofore, the maximum differential in lowering speeds obtainable was from about feet per minute under light load to 60 feet per minute under heavy load, and even this reduced range did not eliminate the objectionable features of an initial sudden drop of the load. The relatively free flow for lifting is provided at all times, regardless of the throttling setting of the member 30. It is generally undesirable to put any limiting means on the lifting speed, as this is readily controlled by the operator himself and there is no danger of a sudden drop, as in lowering of the load.

For purposes of illustration, the valve member 30 is shown as movable along a predetermined path toward and away from the seat and as rotatable for changing the effective orifice area, and thus is movable in a plane transversely of the path. However, it is apparent that instead of rotation of the member 30 to obtain movement in said plane, the member may have movement in said plane for metering other than rotational movement.

Having thus described my invention, I claim:

1. A load lowering valve comprising a hollow body having an inlet and an outlet, and a wall thercbetween having orifice means therein;

settable throttling valve means in the body and operable to permit a relatively large orifice area for flow of pressure fluid from a source through the body from the inlet to the outlet, and settable to restrict the orifice area for flow from the outlet to the inlet in varying degrees in relation to the setting of the valve means,

means normally urging the valve means to a position for maximum orifice area for flow of fluid from the outlet to the inlet,

fluid pressure operable means connected to the valve means and arranged to be subjected to the pressure of fluid in the body during changes in said pressure and operable thereby to set the valve means, during the increase of pressure of the fluid at the outlet side, for exposing decrescent degrees of orifice area 9 for flow from the outlet to the inlet.

and means to hold the valve means in the set position beginning before the occurrence of substantial flow of pressure fluid from the outlet to the inlet and continuing during subsequent flow from the outlet to the inlet past the valve means.

2. The structure according to claim 1 wherein the valve means comprises a valve member, a seat, means supporting the valve member at the outlet side of the seat for moving in a path to and from the seat and for movement :relative to the seat in a plane intersecting said path to set positions, said seat has an orifice, and said member has an orifice positionable in different degrees of registry with the seat orifice upon movement of the member relative to the seat in said plane.

3. A control valve comprising a hollow body having an inlet and an outlet,

a seat in the body having orifice means therein,

a valve member at the outlet side of the seat,

means supporting the member for movement in a path toward and away from the seat to closed and open positions, respectively, and for movement relative to the seat in a plane intersecting said path,

said member having orifice means registerable in different degrees with the orifice means of the seat, depending on the position to which the member is moved in said plane, such that the degree of registry decreases when the member is moved in said plane in one direction and increases when the member is moved in said plane in the opposite direction,

fluid pressure operable means connected to the member and positioned to be continuously subjected to the pressure of fluid in the body and to be continuously operable thereby to move the member in said one direction to decrease said degree of registry as fluid pressure in the body increases,

means yieldably urging the member toward the seat,

means to hold the member in the position to which it is moved in said plane by the fluid pressure operable means before substantial flow of pressure fluid from the outlet to the inlet can occur, and

means yieldably urging the member to move in said opposite direction in said plane to increase the degree of registry.

4. A control valve comprising a hollow body having an inlet adapted for connection to a source of pressurized fluid and an outlet adapted for connection to a fluid load circuit,

a seat in the body between the inlet and outlet,

a valve member,

supporting means supporting the valve member in the body at the outlet side of the seat for movement in a path to and from seated relation to the seat and for movement relative to the seat in a plane intersecting said path,

said seat and member having orifice means therein, re-

spectively, which are fully open when the member is unseated and which are alignable to a decreasing degree upon movement of the member in said plane in one direction and to an increasing degree upon movement of the member in said plane in the opposite direction;

spring means yieldably urging the member in said opposite direction;

seating spring means yieldably urging the member endwise against the seat;

said valve member being movable to unseated position by the pressure fluid when the total pressure of fluid on the valve member at the inlet side of the seat exceeds the pressure of the seating spring means plus the total pressure of the fluid on the valve member at the outlet side of the seat; and

fluid pressure operable means connected to the member and arranged to be subjected continuously to, and to be responsive to, the pressure of fluid in the body and operable thereby for moving the member progressively farther in said one direction against the force of said spring means as the fluid pressure in the body increases from a predetermined minimum while the differential in pressure between the inlet and Outlet sides is insuflicient to seat the member firmly,

5. The structure according to claim 4 wherein the supporting means support the member in the body so that the movement of the member in said plane is rotational movement, the seating spring means yieldably urging the member against the seat and the spring means urging the member to rotate, in said opposite direction are the same means and comprise a spring connecting the body and member to exert both torsional and axial forces on the member concurrently.

6. The structure according to claim 4 wherein the supporting means support the member in the body so that the movement in said plane is rotational movement, the seat is a partition wall in the body, the member has an end wall complementary to and normally seating on a portion of the partition wall, the said portion of the partition wall has orifices spaced radially outwardly from the axis of rotation of the member and spaced apart from each other circumferentially of said axis, and the member has a portion in its end wall with orifices spaced radially outwardly from said axis and spaced apart from each other circumferentially of said axis, for different degrees of registry with the orifices of said portion of the partition wall, depending upon the rotated position of the member.

7. A structure according to claim 6 wherein the orifices in one of said portions are spaced different distances apart circumferentially of said axis than are the orifices in the other of said portions so that the degree of registry of the orifices of the portions increases and decreases in a Vernier relation.

8. The structure according to claim 1 wherein the pressure operable means is a cylinder, a piston therein, means drivingly connecting one end of the piston to the throttling valve means, and said cylinder is connected to the interior of the valve body at the outlet side of the valve means so that said one end of the piston is subject to the fluid pressure at said outlet side.

9. The structure according to claim 8 wherein the valve means includes a rotatable member, an element rotatable therewith, and the valve means and piston are connected to the element.

10. A control valve comprising a hollow body having an inlet and an outlet,

a seat in the body,

a normally seated valve means in the body and operable to be unseated upon movement in one direction along a predetermined path by pressure fluid admitted through the inlet so as to permit a relatively free flow of fluid through the body from the inlet to the outlet, said valve means being settable in selected positions in a plane transverse to said path while unseated for restricting the flow through the body from the outlet to the inlet to varying degrees when the valve means becomes reseated,

sensing means connected to the valve means and responsive to the pressure within the body for setting the valve means for decreasing the restriction in relation to the increase in pressure in the body and for holding the valve means in the set position during return of the valve means to seated position,

and means to frictionally bind the valve means against the seat, upon its return to seated position, in the position in said plane in which it has been set while unseated.

11. A load lowering control valve device comprising a valve having an inlet and an outlet and operable by pressure fluid supplied to its inlet to open and permit a relatively rapid flow of fluid to the outlet,

metering means for restricting the return of fluid through the valve when the valve is in closed position,

said metering means being settable, while the valve is free from subjection to appreciable differentials in pressure at its opposite sides, or varying the restriction,

means yieldably urging the valve to closed position,

sensing means responsive to said fluid pressure for setting the metering means, while the valve is free from said subjection to a position to increase the restriction as the pressure increases,

and means operable consequent upon closure of the valve while the metering means is in set position to frictionally hold the metering means in said set position.

12. A load lowering control valve device comprising a hollow body having an inlet and an outlet;

a stationary wall in the body between the inlet and outlet and having orifice means therein for permitting pressure fluid to pass from the inlet to the outlet and return,

a valve member,

means on the stationary wall supporting the member at the outlet side of the Wall in alignment with the orifice means for movemnt toward and away from the Wall to closed and open positions, and for rotation about an axis normal to said Wall;

said member having orifice means registerable with the wall orifice means in varying degrees dependent upon the rotated position of the member;

a combined torsion and compression spring operatively connected to the member and body and yieldably holding the member seated on said wall and yieldably urging the member to rotate about said axis in one direction to a rotated position wherein the orifices are in maximum registry;

a cylinder connected to the body and in communication with the interior of the body;

a piston in the cylinder and driven in one direction in response to the pressure of said fluid;

means connecting the piston to the member for rotating the member against the resistance of the spring when the piston is driven in its said one direction for reducing the degree of registry of the orifices in proportion to the increase in said fluid pressure;

and said member frictionally binding against said wall, when seated by a positive difierential in pressure of the fluid at the outlet side relative to the pressure of the fluid at the inlet side, with sufficient force to prevent rotation of the member in. its said one direction of rotation by the spring toward maximum registry of the orifices.

References Cited UNITED STATES PATENTS 706,306 8/1902 Ewart 267-9 934,932 9/1909 Osbourn 25206 2,983,280 4/1961 Maison 137-50547 FOREIGN PATENTS 62,860 6/1892 Germany.

WILLIAM F. ODEA, Primary Examiner.

H. M. COHN, Assistant Examiner.