WO1994001709A1

WO1994001709A1 - Compensated valve

Info

Publication number: WO1994001709A1
Application number: PCT/US1992/005651
Authority: WO
Inventors: James A. Pena
Original assignee: Servojet Electronic Systems, Ltd.
Priority date: 1992-07-10
Filing date: 1992-07-10
Publication date: 1994-01-20

Abstract

A fluid pressure balanced valve is used in directing fluid from a supply passage (11) to an outlet. A ball valve (1) has a sealing portion (20) cooperating with a seat (3). Balancing elements (8, 14) impose on ball valve (1) equal and opposite forces arising from the static pressure at supply passage (11). Balancing element (14) also has an annular space (19) adapted to receive a force equal and opposite to the force applied to ball valve (1) arising from the dynamic pressure of the fluid when the valve is open resulting in the net forces arising from fluid pressure acting on the ball valve (1) to be zero. A duct (22) transmits dynamic pressure to a balancing element (8) to diminish any forces tending to close the sealing portion (20) on to the seating portion (3).

Description

COMPENSATED VALVE This invention relates particularly to pressure compensated fluid valves. Hydraulic valves are known which move between two rest positions and in which in each of the two rest positions the valve is balanced by the static hydraulic forces acting on it so that only a small force is required to move it in the direction of the other position. Whilst the valve is in transition from one position to the other the hydraulic forces acting on the valve change because of flow through the valve and the valve may be influenced by dynamic as well as static hydraulically generated forces. Such a mix of hydraulic forces may cause the valve to undesirably reseat on the first position. Indeed whilst the fluid is flowing from one port to another the hydraulic forces caused by variation of flow may cause the valve to reseat on the first position a relatively long while after the valve may have seated on the second position.

This tendency may be overcome for instance by making sure that the small initiating force is large enough to ensure displacement to the other position. However, it is undesirable to have to provide extra actuating capacity or to limit pressure or other parameters to ensure correct operation.

The present invention has for its primary objective the provision of a valve of the type stated in which the static and dynamic hydraulic forces generated by its operation cooperate to prevent unintentional reseating. A secondary objective is to balance the valve under static and dynamic hydraulic forces acting on it at all times and a tertiary objective is to move the valve positively away from its seat. Accordingly the present invention is a valve for use in directing fluid from a supply port to a service port and comprises a movable element having a sealing portion, a fixed element having a seating portion, a fixed element having a seating portion adapted to cooperate with the sealing adapted to cooperate with the sealing portion to permit or prevent fluid flow therebetween, a duct positioned closely adjacent said seating portion to transmit the dynamic pressure of fluid flowing between the seating and sealing portions, a compensating element connected to said duct and adapted to apply a force derived from said dynamic pressure to said movable element in a direction to diminish any forces trying to close the sealing portion onto the seating portion. As a first preference the compensating element is one of two balancing elements adapted to impose on the movable element equal and opposite balancing forces arising from the static pressure of supply fluid, one balancing element being adapted also to receive an equal and opposite force to that applied to the movable element arising from the dynamic pressure in the duct.

As a second preference the compensating element is one of tow compensating elements the first of these being adapted to impose on the movable element a first force derived from the pressure in the duct and the second compensating element being adapted to impose on the movable element a second force directed oppositely to the first force and derived from pressure of fluid in the supply port, the resultant of such separate the sealing and seating portions under conditions of fluid flow therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by reference to the accompanying drawings which represent the modes of carrying the invention into effect.

Figure 1 is a schematic representation of a statically balanced valve according to the prior art,

Figure 2 is a schematic representation of a first embodiment of the valve, Figure 2A is an enlargement of part of the valve of Figure 2,

Figure 3 is a schematic representation of a second embodiment of the valve, and

MODES OF CARRYING OUT THE INVENTION

Figure 1 schematically represents a statically balanced valve of the prior art. the movable element of the valve is conveniently a hard steel ball 1 which moves in a housing 2 to seal against a seat 3 to prevent flow of supply fluid from a supply port 4 into a service port 5. In its alternative position it seals against a seat 6 to prevent flow from the service port 5 to a vent port 7. The supply port 4 and vent port 7 are often a single bore for convenience and a piston 8 and rod 9 are contained in the cylinder 10 so formed, the rod 9 being arranged to contact the ball. A passage 11 connects the cylinder 10 with the supply port 4.

The ball 1 may be kept on the seat 3 by an actuator 12 operable by eg. a solenoid 13 acting through piston 8 and rod 9 so that operation of the solenoid will allow the ball 1 to lift from seat 3. When these valves are used in high frequency applications it is desireable to use the lightest possible actuation forces. Accordingly the ball is subjected to supply pressure at port 4 and an equal and opposite force transmitted by piston 8 and rod 9 to balance it. With no flow the ball will be balanced whilst resting on seats 3 or 6. However, it is not in

SUBSTITUTE SHEET balance when moving between them or when fluid is moving from supply port 4 to service port 5 because the pressure from the supply port side 4 near the seat 3 will be a dynamic pressure and therefore less than the static pressure in cylinder 10 causing a tendency for it to reseat. The service port 5 may be connected to apparatus which has valves which open and shut quickly giving rise to perturbations which are transmitted back to the ball 1 and may cause or assist in unintentional reseating of the ball on seat 3.

The invention now to be described with reference to Figures 2 and 3 seeks to diminish the tendency to reseat. In the case of the embodiment of Figure 2 the embodiment will cause perfect theoretical balancing of the valve and in case of Figure 3 the embodiment will over-compensate and provide an active bias towards seat 6.

The description with reference to Figures 2 and 3 will use the same reference numbers as those used in Figure 1 to denote the same parts.

Referring to the schematic drawing Figure 2 it will be seen that the bore forming the supply port 4 and the vent port 7 now contains an additional piston 14 at the supply port end which is hydraulically sealed and slidable in the bore and defines a cylinder 15. The upper end of piston 14, the ball and the seat 3 are seen enlarged in Figure 2A. the nose 16 of the piston 14 is counter bored at 17 and the protruding land 18 is lapped so that is acquires a spherical surface to enable it to seal fluid tightly on the ball 1. The outer diameter 'd' of the nose 16 is less than the diameter 'D' of the bore and the seat 3 leaving an annular space 19 to enable flow of supply fluid to reach and pass between the seating portion or seat 3 and the sealing portion 20 on the ball 1 which makes contact with the seat 3. The supply fluid enters cylinder 10 through passage 11, enters into cylinder 15 through passage 21 and into annular space 19 through passage 21 A. When the ball 1 is seated the force acting upwards on the ball is the force from the static pressure of the supply fluid acting over the area of the piston 14. The force acting downwards will be the same static pressure acting on the piston 8, which has the same area as piston 14. Hence the valve is statically balanced.

When the ball 1 is moved off its seat by an outside force the full static pressure is still applied to pistons 14 and 8 acting through the land 18 and the piston rod 9 respectively on the ball 1 and the forces arising from these will be equal and opposite. The dynamic pressure of the fluid flowing through the annular space 19 and past the seating portion 3 and sealing portion 20 will act upwardly on the projected area of the annular space on the ball 1 and downwardly on the same projected area on the piston 14. The annular space 19 itself constitutes a duct for transmission of the dynamic pressure to the piston 14 which constitutes a compensating element. Accordingly there will be a balance of the forces arising from dynamic pressures at all states of flow. Thus the natural tendency to reseat is diminished to zero in this embodiment. Passage 21 A will be under full static pressure during flow because the flow area does no reduce until the annular space 19 is reached.

Referring now to the schematic drawing Figure 3, it will be seen that the piston 8 and 14 are present in their respective cylinders 10 and 15 and that the annular space 19 around the nose 16 of piston 14 is present. However the passage 22 which leads to the annular space 19 is connected to cylinder 10 only through passage 23, whilst the supply is connected to the cylinder 15 through passage 24. The piston 14 in this case is bored longitudinally and transversely to provide a passage 25 to enable supply fluid to reach the annular space 19 which again, with the separation between seat portion 3 and sealing portion 20 on the ball constitutes a constriction of flow giving rise to a dynamic pressure which is less than the static pressure. When the sealing portion 20 of the ball is seated on the seating portion 3 the static pressure of the supply fluid exerts through the piston 14 and the projected area of the annular space 19 an upward force on the ball 1 which is balanced by the static pressure acting though passage 23 and cylinder 10 on the piston 8 to produce an opposite and equal downward force acting through rod 9. At this point the valve is statically balanced. When the ball is moved off its seat by an outside force the flow immediately starts and the pressure becomes a dynamic one which is less than the static pressure, this lower pressure is signalled to the cylinder 10 through passage 23 and the ball 1 is unbalanced in a direction which moves it towards and on to the seat 6. It is to be noted that the annular space 19 and the passage 23 constitute a duct for leading dynamic pressure to the piston 10 which constitutes a compensating element. The piston 14 follows up and it is also to be noted that the axial length of the annular space 19 permits this movement without preserving the depressed dynamic pressure throughout the movement.

The effect of the Figure 3 valve is to diminish the reseating tendency to the extent that the ball becomes positively biased away from the seat 3. This means that by suitable choice of dimensions it becomes possible to cater for significant pressure perturbations arriving from pressure-wave generating apparatus served by the service port, and for the relative speed at which the ball may move in comparison with the rise or decay of pressure in the service port. It is often the case that the actuator 12 operates to move the ball off the vent valve seat 6 very positively and so the actuator 12 is often made to act directly and push it off. It is necessary that the action of opening the supply port is certain. The invention contributes to such certainty. In the case when the ball is moving on the reverse transit from seat 6 to seat 3 the service has been filled and there is no flow from the supply. In these circumstances the valve is under perfect static balance and can be moved easily by the actuator 12, thus enabling the latter to be reduced in size and consume less power.

The valves of the invention have particular use in hydraulic applications where the service port may remain open to a cylinder or other actuator for a relatively long period of time and where the pressure in this port rises slowly and causes a condition of pressure imbalance because of the continuing flow past the ball creating an ongoing depression, the invention compensates throughout the time period when flow from the supply causes a pressure drop at the seating portion and moreover does so irrespective of the frequency. The valves of the invention have particular use in high speed applications for instance where fuel, being a hydraulic medium needs to be pulsed to fuel injection apparatus at varying rates for consumption in, for instance, a diesel engine.

SUBSTITUTE SHEET

Claims

1. A valve for use in directing fluid from a supply port to a service port comprises a movable element having a sealing portion, a fixed element having a seating portion adapted to cooperate with the sealing portion to permit or prevent fluid flow therebetween, a duct positioned closely adjacent said seating portion to transmit the dynamic pressure of fluid flowing between the seating and sealing portions, a compensating element connected to said duct and adapted to apply a force derived from said dynamic pressure to said movable element in a direction to diminish any forces trying to close the sealing portion on to the seating portion.

2. A valve as claimed in claim 1 wherein said compensating element is one of two balancing elements adapted to impose on the movable element equal and opposite balancing forces arising from the static pressure of supply fluid, one said balancing element being adapted also to receive an equal and opposite force to that applied to said movable element arising from the dynamic pressure in said duct.

3. A valve as claimed in claim 1 wherein said compensating element is one of two compensating elements said first element a first force derived from said pressure in said duct and the second compensating element being adapted to impose on the movable element a second force directed oppositely to said first force and derived from pressure of fluid in said supply port, the resultant of such first and second forces being in a direction to further separate the sealing and seating portions under conditions of fluid flow therebetween.

4. A valve as claimed in claim 2 wherein said one balancing element is formed to provide an annular space in the vicinity of said movable element to enable passage of supply fluid to and between said sealing and seating portions.

5. A valve as claimed in claim 4 wherein said one balancing element is separable from said movable element but is sealingly engageable with it at least at the radially inner boundary of said annular space, under the force exerted by said static pressure.

6. A valve as claimed in claim 5 wherein both said balancing elements are constituted by tow oppositely directed piston and cylinder units containing fluid which, in operation, is always at the static pressure of the supply fluid.

7. A valve as claimed in claim 6 wherein said maximum separation is set by a stop for the movable member.

8. A valve as claimed in claim 7 wherein said stop is constituted by a second valve sealing portion adapted to receive a second valve seating portion on the movable element.

9. A valve as claimed in claim 8 wherein the second valve seating portion and the second valve sealing portion between them define a closeable passage leading from said service port to a vent port.

10. A valve as claimed in claim 3 wherein said second compensating element is formed to provide an annular space in the vicinity of the movable element to enable passage of supply fluid to and between said sealing and seating portions said duct being arranged to open into said annular space and transmit the dynamic pressure of fluid in the vicinity of said sealing and seating portions.

11. A valve as claimed in claim 10 wherein said compensating elements are constituted by two oppositely directed piston and cylinder units.

12. A valve as claimed in claim 11 wherein the piston of the piston and cylinder unit which is under supply pressure is apertured to allow through passage of supply fluid to the seating portion.

13. A valve as claimed in claim 10 wherein said annular space is of sufficient length as to avoid variation of dynamic pressure in said duct throughout the travel of the second compensating element.

14. A valve as claimed in claim 13 wherein said maximum separation is set by a stop for the movable member.

SUBSTITUTE SHEET

15. A valve as claimed in claim 14 wherein said stop is constituted by a second valve sealing portion adapted to receive a second valve seating portion on the movable element.

16. A valve as claimed in claim 15 wherein the second valve seating portion and the second valve sealing portion between them define a closeable passage leading from said service port to a vent port.

17. A valve as claimed in any one of the preceding claims wherein said movable element is constituted by a spherical ball.

18. A valve as claimed in any one of the preceding claims wherein said fixed element is constituted by a valve housing which contains said supply port and service port.

19. A valve as claimed in claim 4 or claim 10 wherein the radial width of said annular space is of the order of the maximum separation of the sealing portion and the seating portion.

20. A method of compensating a hydraulic valve of the type which is capable of being balanced under static pressures whilst sealing on a seat comprises the step of applying the reduced pressure arising from dynamic flow of fluid near said seat to said valve so that the net forces acting on said valve is in a direction to maintain said valve in an unseated condition whilst flow persists.