GB2164423A

GB2164423A - Control valve

Info

Publication number: GB2164423A
Application number: GB08522141A
Authority: GB
Inventors: James Kevin Fretwell
Original assignee: BESTOBELL
Current assignee: BESTOBELL
Priority date: 1984-09-11
Filing date: 1985-09-06
Publication date: 1986-03-19
Also published as: GB8422927D0; GB2164423B; GB8522141D0

Abstract

A control valve has an annular groove (17) in a closure disc (8), which can cooperate with a seating (7) to isolate an inlet (5) and an outlet (6) from one another. This groove (17) allows, via passageways (15, 16) the fluid upstream of the disc (8) to act on a piston (11) to balance the force acting on the disc (8). Since the groove (17) is located adjacent to the seating (7), the pressure fed to the piston (11) is the mean effective static pressure across the disc (8), thereby enabling the force to be balanced even when the disc (8) moves away from the seating (7). <IMAGE>

Description

SPECIFICATION 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, In use, the actuator controls the position of the closure member and hence fluid flow downstream of the valve.

The pressure sensitive device is conventionally a piston or diaphragm which is subjected to the inlet fluid pressure, that is the fluid pressure which is applied to the upstream face of the valve closure member when the seating is closed by the closure member. Although this may be arranged to balance the static pressure on the closure member when the valve is closed, it will not do so when the closure member moves away from the seating, owing to the appreciable rise in the fluid velocity through the seating and around the closure member, which results in a drop in static pressure on the upstream side of the closure member. This results in an out of balance situation giving unreliable control and operating conditions and requiring modification to the control actuator or even the use of a secondary actuator linked by some means to the downstream pressure.

The object of the present invention is to devise a simple modification to a conventional valve whereby the static pressure across the closure member can be more effectively compensated when the valve is open.

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 and the tapped pressure is utilized for the pressure responsive device.

Surprisingly, it has been 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. This enables a simple control acuator to be used, such a spring or motor, as it does not have to take account of any out of balance forces.

The pressure tapping could be through a static part, such as through the seating or part of the housing. Preferably, however, the tapping is through the closure member itself. Thus the tapping may be provided by an annular groove around the upstream edge of the closure member and hence via one or more radial passages and an axial passageway in a stem of the closure member, to a chamber which is isolated from the fluid flowing through the valve housing, where it acts upon a piston or diaphragm connected to the closure member stem.

The invention will now be described in more detail with respect to the accompanying drawings, in which: Figure 1 is an axial section through a conventional control valve; Figure 2 is a similar section through a control valve in accordance with the invention; and, Figure 3 is a diagrammatic enlargement of part of Fig. 2.

The valve shown in Fig. 1 has a housing 4 with an inlet 5 and an outlet 6, and an annular frustoconical seating 7. A valve closure disc 8 cooperates with the seating and is carried by a stem 9, forming a control member, and the continuation 10 of which carries a compensating piston 11 which works in a cylindrical portion 12 of the housing. The control member 9 will be moved by means of q control actuator shown diagrammatically at 13.

When the valve is closed, and the disc 8 is seated on the seating 7, the static pressure F1 acting on the underside of the disc is compensated by the static pressure F2 acting on the compensating piston 11, so that the valve may be opened using only a small force from the control actuator 13. However, as soon as the disc 8 moves away from the seating 7, the velocity through the annular gap reduces the static pressure F1 and produces out of balance forces.

The valve constructed in accordance with the invention, and shown in Figs. 2 and 3, differs from the conventional valve of Fig. 1 in that the cylindrical portion 12 of the housing is sealed from the flow path through the housing by means of a cross wall 14 through which the stem 10 slides. The stem 10 includes an axial bore 15 which opens at one end into the cylindrical portion 12, and at the other end via two or more radial bores 16 into an annular groove 1 7 which is exposed to the fluid pressure on the upstream side of the closure disc 8 immediately adjacent to the seating 7. As shown in Fig. 3, the groove 17 is provided between an annular undersurface 18 of the closure disc 8 and a radially projecting tapering flange 19 of smaller radial extent than the surface 18. This ensure that the static pressure at the circular iocus of the point 20 is transmitted to the cylindrical portion 12 irrespective of whether the closure disc 8 is closed against the seating 7 or not. As the closure disc opens away from the seating, the static pressure at the point 20 will diminish and this will be reflective immediately by a reduction in the force F1 and a compensating reduction in the force F2.

Since the velocity of fluid flow through the annular gap between the seating 7 and closure disc 8 is essentially perpendicular to the radial extent of the groove 17, and the passages 16, the pressure tapped off and supplied to the cylindrical portion 12 is effectively independent of any velocity pressure component.

Claims

1. A control valve 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; characterized in that a static fluid pressure tapping is taken within the housing adjacent to the seating and the tapped pressure is utilized for the pressure responsive device.

2. A valve according to claim 1, in which the pressure tapping is taken through the closure member

3. A valve according to claim 2, in which the pressure tapping is provided by an annular groove around the upstream edge of the closure member, and hence via one or more radial passages and an axial passageway in a stem of the closure member, to a chamber which is isolated from the fluid flowing through the valve housing, where it acts upon a piston or diaphragm connected to the closure member stem.

4. A control valve substantially as described with reference to Figs. 2 and 3 of the accompanying drawings.