GB2231643A

GB2231643A - Pressure-compensated valve

Info

Publication number: GB2231643A
Application number: GB9007468A
Authority: GB
Inventors: James Kevin Fretwell; Ernest Walter Mabon
Original assignee: Meggitt France SAS; WILLIAM EAGLES Ltd
Current assignee: Meggitt France SAS; WILLIAM EAGLES Ltd
Priority date: 1989-05-18
Filing date: 1990-04-03
Publication date: 1990-11-21
Anticipated expiration: 2010-04-03
Also published as: GB2231643B; GB9007468D0; GB8911436D0

Abstract

To compensate static fluid pressure difference across the closure member of a control valve a static fluid pressure tapping is taken within the housing adjacent to the seating (9) by means of a passageway (32) extending from the seating, through the wall of the housing, to an externally mounted subsidiary valve (33), and hence back through the wall of the housing to a chamber (22), which is isolated from the fluid flowing through the valve housing, and where it acts upon a piston or a diaphragm connected to the closure member stem. The valve (33) allows the pressure compensation to be switched off but in this closed position of the valve (33) a mechanical interlock (36) prevents operation of the control wheel (13) of the main valve. <IMAGE>

Description

DESCRIPTION CONTROL VALVE The invention is concerned with a control valve of the kind, hereinafter referred to as of the kind described, comprising a housing with a fluid inlet and a fluid outlet interconnected within the housing through a seating; a valve closure member which cooperates with the seating to open and close the fluid passageway through the housing from the inlet to the outlet, the closure member being connected to a control member which extends out of the housing for connection to an actuator; and a pressure responsive device for compensating static fluid pressure difference across the control member.

GB-A-2164423 discloses a control valve of the kind described in which a static fluid pressure tapping is taken within the housing adjacent to the seating and the tapped pressure is utilised for the pressure responsive device. It is found that this simple expedient enables the use of the mean effective static pressure across the closure member at any operating position of the valve to be available for the compensating action of the pressure sensitive device. This provides a substantially reliable balancing of the closure member and hence the accurate control of the closure member by a related control actuator to which it is connected via the control member.

There are times when it would be desirable to deactivate the pressure responsive device for operation of the valve in a high pressure mode.

However, in the particular valve described and illustrated in 2164423, the fluid pressure tapping is taken through the closure member itself, and hence through the stem of the closure member to a chamber which is isolated from the fluid flowing through the valve housing, where it acted upon a piston of diaphragm connected to the closure member stem. The pressure tapping was thus permanently open and inaccessible externally of the valve.

In accordance with the present invention, in a control valve of the kind described, a static fluid pressure tapping is taken within the housing adjacent to the seating by means of a passageway extending from the seating, through the wall of the housing, to an externally mounted subsidiary valve, and hence back through the wall of the housing to a chamber, which is isolated from the fluid flowing through the valve housing, and where it acts upon a piston or a diaphragm connected to the closure member stem. With this arrangement, the externally accessible subsidiary valve can be operated to open or close the tapping between the seating and the chamber so that the valve may simply be switched over between balanced and high pressure modes.

The invention is particularly applicable to a control valve of the kind having two coaxial stem parts. A first stem part carries the closure member and is acted upon both by the piston or diaphragm and by a control spring, preferably of adjustable spring rate. The second stem part will then carry a handle for screwing down to force the closure member to its closed position. When the second stem part and handle are unscrewed, the throttling effect of the closure and seating will then be dependent upon the pressure difference across the closure member, the action of the spring, and any pressure compensating effect of the piston or diaphragm if the subsidiary valve is open.

To avoid shock loading, it may be desirable to ensure that the second stem part and handle cannot be rotated in either direction except when in the pressure compensating mode with the subsidiary valve open. This may be achieved by a simple mechanical interlock between the handle on the second stem and a handle on the subsidiary valve. For example an axially slidable pin may be located between the two handles so that one end of the pin engages abutments on the control valve handle to prevent movement of that handle unless the subsidiary valve handle is in its valve open position, in which case the other end of the pin is free to enter an opening in a part which moves with the subsidiary valve handle, thereby disengaging the pin from the control valve handle.

In order to avoid build up of incompressible liquid in the piston or diaphragm chamber, the subsidiary valve may be arranged, in the closed position, to close the passage from the seating, but to connect the passage from the chamber to a bleed port. The subsidiary valve is preferably a rotatable cock.

An example of a valve constructed in accordance with the present invention is illustrated in the accompanying informal drawings, in which: Figure 1 is a vertical section through the valve; Figure 2 is a vertical section through the valve taken at right angles to the section of Figure 1; and, Figure 3 is a sketch showing part of a mechanical interlock with the subsidiary valve handle.

The illustrated control valve has an upper housing part 4, a main housing part 5, formed with an inlet flange 6 and an outlet 7, and a lower housing part 8, the housing parts being screwed together.

The housing part 5 is formed with an integral seating 9. An upper stem part 10 extends through the upper housing part 4 and is sealed to it by a gland nut 11 and O-ring 12. At its upper end the stem part 10 carries a handle in the form of a wheel 13, which is held keyed on the stem by a nut 14. The stem part 10 carries a screw threaded bush 15 which screws through a complementary screw threaded bore in the upper housing part 4.

The lower end of the stem part 10 extends into a socket 16 at the upper end of a lower stem part 17 which carries a valve closure member 18 for cooperation with the seating 9, and hence control the flow of fluid from an inlet 20 in the flange 6 through the seating 9, and out of the outlet 7. The stem part 17 passes through a web 21 in the bottom of the main body part 5, to which it is sealed by an O-ring.

In the body part 5, below the web 21, is a cylindrical chamber 22, in which there works a piston 23 having a peripheral O-sealing ring 24. The piston 23 is fixed on the lower stem part 17, by lock nuts 25 and hence moves with the closure member 18.

The lower housing part 8 carries an upwardly projecting externally screw threaded post 26, which is held in position by a nut 27 which is accessible when a bottom cover 28 is unscrewed and removed. A plate 29 is screwed on and therefore vertically adjustable on the post 26 but is prevented from leaving the upper end of the post by means of an annular abutment 30. The plate 29 acts as a reaction for the lower end of a helically coiled compression spring 31 the upper end of which acts on the underside of the piston 23. Adjustment of the plate 29 adjusts the spring rate.

As shown in Figure 2, a pressure tapping is taken from the seating 9 by means of a first passageway 32 leading through the wall of the main body part 5 to an inlet port of a rotary cock valve 33. When the cock is in its open position, as determined by the position of a rotary handle 34, the inlet port is in communication via a rotary spool with an outlet port, leading through a second passage 35 through the wall of the main body part 5, into the chamber 22. This provides the pressure compensating mode as the static pressure at the seating is transmitted to the chamber 22 and hence acts substantially equally on the underside of the closure member 18 and on the upperside of the piston 23, the resulting reactions balancing one another.

The valve can be changed over to the high pressure mode by rotating the handle 34 through a 1800, such that the inlet port of the valve 33 is closed. In this configuration the outlet port of the valve 33 is connected to a bleed port so that incompressible liquid cannot be trapped in the chamber 22.

A mechanical interlock between the wheel 13 and handle 34 is provided by a locking pin 36 which is slidable in the arms of a yoke 37 mounted on the upper housing part 4. The range of movement is limited by an abutment 38 which engages the arms of the yoke in limiting positions. As shown in Figure 3, the handle 34 has a hole 39 into which the lower end of the pin 36 can drop when the valve 33 is in its open position. Only in this lowered position of the pin 36 is the wheel 13 free to be rotated either to open or close the control valve. Conversely, when the valve 33 is closed, as shown in Figure 3, the pin 36 must be in its raised position in which its upper end engages spokes on the underside of the wheel 13 and prevents rotation of the wheel. In this way it is not possible for the valve to be opened or closed except in the pressure compensating mode.

Claims

1. A control valve of the kind described, wherein a static fluid pressure tapping is taken within the housing adjacent to the seating by means of a passageway extending from the seating, through the wall of the housing, to an externally mounted subsidiary valve, and hence back through the wall of the housing to a chamber, which is isolated from the fluid flowing through the valve housing, and where it acts upon a piston or a diaphragm connected to the closure member stem.

2. A valve according to claim 1, of the kind having two coaxial stem parts, a first stem part carrying the closure member and being acted upon both by the piston or diaphragm and by a control spring, and the second stem part carrying a handle for screwing down to force the closure member to its closed position.

3. A valve according to claim 1 or claim 2, wherein the second stem part and handle cannot be rotated in either direction except when in the pressure compensating mode with the subsidiary valve open, by virtue of a simple mechanical interlock between the handle on the second stem and a handle on the subsidiary valve.

4. A valve according to claim 3, wherein the mechanism interlock is provided by an axially slidable pin which is located between the two handles so that one end of the pin engages abutments on the control valve handle to prevent movement of that handle unless the subsidiary valve handle is in its valve open position, in which case the other end of the pin is free to enter an opening in a part which moves with the subsidiary valve handle, thereby disengaging the pin from the control valve handle.

5. A valve according to any one of the preceding claims, wherein, in order to avoid build up of incompressible liquid in the piston or diaphragm chamber, the subsidiary valve is arranged, in the closed position, to close the passage from the seating, but to connect the passage from the chamber to a bleed port.

6. A valve according to any one of the preceding claims, wherein the subsidiary valve is a rotatable cock.

7. A control valve substantially as described with reference to the accompanying drawings.