GB2060139A

GB2060139A - Control Valve

Info

Publication number: GB2060139A
Application number: GB8024430A
Authority: GB
Original assignee: Advanced Semiconductor Materials NV; Advanced Semiconductor Materials America Inc
Current assignee: Advanced Semiconductor Materials NV; Advanced Semiconductor Materials America Inc
Priority date: 1979-07-26
Filing date: 1980-07-25
Publication date: 1981-04-29
Also published as: GB2060139B; DE3028712A1; FR2462638B3; JPS5620884A; NL7905792A; FR2462638A1

Abstract

A control valve for a gas or liquid flow, comprises a housing (1), separated by a wall (2) into two chambers (3 and 4), each chamber (3, 4) being provided with a supply connection (5) or discharge connection (6), a valve orifice (7) in the wall (2), a valve member (8) which can close the valve orifice (7) completely or can open or close it further, a valve stem (9, 10) extending on both sides of the valve member (8) through the chambers (4, 3), which valve stem on one end extends to the outside of the housing (1) and being provided with an actuator, whereby in both chambers (3, 4) a bellows (12, 13) is present and the active area of both bellows (12, 13) is equal to or substantially equal to the active area of the valve member (8) and whereby only said actuator determines the position of the valve member (8) with respect to the valve orifice (7) and whereby the bellows may be pretensioned for adjusting the position of the valve member (8) with respect to the valve orifice (7) independent of the actuator. The actuator may be moved by means of a magnet. <IMAGE>

Description

SPECIFICATION Control Valve The invention relates to a control valve for a gas or liquid flow, comprising a housing, separated by a wall into two chambers, each chamber being provided with a supply connection or discharge connection for the flow to be controlled, a valve orifice in the wall, a valve member which can close the valve orifice completely or can open or close it further, a valve stem connected to the valve member, extending on the one side through one of the chambers and outside the housing being provided with an actuator and extending on the other side into the other chamber and flexible bellows in both chambers, on the one side being connected to the housing and on the other side to the valve stem whereby the active area of both bellows is equal to or substantially equal to the active area of the valve member.

Such a valve is known from U.S. Patent Specification 3,304,048 and has the advantage that the force which is required to actuate the valve is substantially independent on the supply pressure or the discharge pressure of the fluid to be controlled. Further a low force is required to control large fluid flows. Moreover, the valve works very quickly.

The known valve comprises in the first mentioned chamber a spring moving valve member to the closed position if the actuator does not function. This actuator has only the purpose to open the valve completely or partly.

The present invention aims to provide a valve, which is able to control a fluid flow very exactly and whereby the valve member in the rest position can have each desired position with respect to the valve orifice.

This is obtained according to the invention in that only said actuator determines the position of the valve member with respect to the valve orifice and that means are provided for adjusting the position of the valve member with respect to the valve orifice independent on the actuator.

In this way it is possible to control the fluid flow very evenly whereby the valve may be open in the rest position. From this rest position the valve may be actuated in order to be closed or to be opened further. This rest position which depends on the required output and on the pressure conditions can be adjusted independent on the actuator by connecting adjustably the valve member to the valve stem and/or to make adjustably the wall in which the valve orifice is provided, with respect to the housing and/or to make adjustably the connecting points between bellows and valve stem.

In order to make the valve safe to explosion according to a further embodiment of the invention, between the valve stem beyond the point where the sealing bellows is connected to the housing, and the housing a diaphragm is arranged, providing for sealing at rupture or leakage of the bellows.

The invention will now be explained with reference to the drawings for an embodiment of the invention, in which drawing a longitudinal section of a control valve according to the invention is shown.

The control valve according to the invention comprises a housing 1, which is divided by a transverse wall 2 into a supply chamber 3 and a discharge chamber 4. The supply connection is indicated with 5 and the discharge connection with 6. In the transverse wall an orifice 7 is provided, which orifice can be closed off by a valve member 8.

The valve member 8 is provided with a valve stem 9, extending through the chamber 4 and through the upper wall of the housing 1. Outside the housing 1 a not-shown actuator is connected to the valve stem 9. This actuator can be a pneumatic, thermic, electromechanic or e)ectromagnetic actuator.

The valve stem projects also beyond the valve member 8 and is indicated there with the reference number 10. Of course, it is not necessary that this valve stem 10 extends beyond the housing 1. It is sufficient that a cap 11 or the like is present for receiving the free end of the valve stem 10.

In both chambers 3 and 4 bellows 12 resp. 13 are provided. These bellows 12 and 13 are on the one side connected to the housing 1 and on the other side to plates 14 resp. 15, which are stiffly connected to the valve stem 10 resp. 9. In the chamber 4 the bellows 13 functions in a known way as sealing of the valve stem 9 with respect to the housing 1. The active areas of the bellows 12 and 13 are as much as possible equal to the area of the orifice 7 to be closed. In the embodiment shown in fig. 1 the not-shown actuator can be carried out as a pushing actuator, that means the actuating force is applied to the valve member 8 in downward direction. The valve is then in the rest position open. However, it is also possible at a pushing actuator to arrange the valve member 8 at the lower side of the wall.In that case a small netto force must act in upward direction by giving the bellows 1 2 and 1 3 a certain pretension, in order also at small pressures in the chamber 3 to obtain a correct closing. Of course, in that case the conical form of the valve member 8 and the conical form of the orifice 7 must be formed in an inversed direction.

However, it is also possible to carry out the actuator as a drawing actuator, that means the actuating force is then acting in upward direction.

When the valve member 8 is arranged at the lower side of the wall 2 and the conicity of the orifice 7 and the valve member 8 are carried out inversed, the valve is open in the rest position.

The orifice 7 remains then free, but the supply must take place through connection 6 and the discharge through connection 5. When the valve member 8 and the orifice 7 are carried out as shown in fig. 1, then at a drawing actuator the bellows 12 and 13 must be given a pretension, so that the orifice 7 is closed in normal condition. At this normal closed embodiment the supply must take place through connection 6 and the discharge through connection 5.

The bellows 12 and 1 3 can fulfil a triple function. The bellows 13 serves for sealing the valve stem 9 with respect to the housing 1 and seals the chamber 3 and 4 leakage-free with respect to the outside.

Both bellows 12 and 13 can apply a pretension and in such a way push the valve member 8 into the orifice 7.

They compensate the forces which are applied by the fluid on the valve member 8. The effective areas of the bellows 12 and 13 must be equal to the area of the orifice 7 in the wall 2.

When in the supply chamber 3 at closed valve a certain fluid pressure prevails and the active area of that part of the valve member 8 which closes the orifice 7, is equal to the active area of the bellows 12, then the same force is acting in upward direction on the valve member 8 and in downward direction on the bellows 12. These forces are thus compensated at the valve according to the invention.

The active area of each bellows can be explained in the following formula: (d Fa) x dP in which Fax is the force applied in axial direction by the fluid on the bellows, when this is arranged in a closed chamber and is open at one end; P is the pressure of the fluid in the chamber around the bellows and the index x indicates: at constant deflection from the balance position.

The valve is nearly proportional since for maintaining a certain position of the valve member 8 the force required therefore in first instance is proportional to the deflection of the valve member 8 from the balance position (this because the bellows 12 and 13 are nearly ideal springs) and this position is nearly proportional to the flow output, provided cases with equal pressures are considered.

In completely or nearly completely opened condition, dependent on the situation, a small change of the force will be of influence on the valve stem 9, 10 at maintaining the position of the valve member 8. The reason for this is that the pressure on the spot of the valve member 8 coheres with the flow liquid according to the Bernouilli Law.

The valve stem 9, 10 is supported in such a way, that the valve member 8 in closed position of the valve rest well in the seating and that friction effects which may lead to hysteresis remain small. For this at 1 6, 17 slide bearings or leaf spring bearings can be used. When the valve stem 10 only extends to the plate 14, a not shown leaf spring bearing with holes for the gas supply can be arranged near the valve member 8 on one side to the valve stem 10 and on the other side to the housing 1. The centering takes then place very near to the critical place. Also the selfcentering action of a conical or circular valve member 8 in a conical orifice 7 can be used as bearing.

In order to obtain an embodiment which is safe for explosion, a diaphragm 18 connected to the valve housing 1 and to the valve stem 9 can be provided that, when the bellows 1 3 breaks down or may leak, is pressed against a fixed abutment 19.

The rest position of the valve, cohering with the required output and the pressure conditions, can be adjusted by making adjustably the valve member 8 over the valve stem 10 for instance by threading (in combination with a locking nut), by a displaceable seating plate 2 or by displaceable bellows flanges 14 and 15. This is not shown in the drawings.

The actuating takes place for instance by arranging a drawing or pushing magnet above the housing 1. This magnet may apply only axial forces and no transverse forces to the valve stem 9, 10. The magnet is a proportional control magnet, that means in the functional range the applied force is proportinal to the controlling current through the spool and independent on the stroke. In this way the output if measured at the same pressures is in the first order linear dependent on the controlling current, since the output in the first order linearly depends on the force acting on the valve stem 9.

Claims

1. Control valve for a gas or liquid flow, comprising a housing, separated by a wall into two chambers, each chamber being provided with a supply connection or discharge connection for the flow to be controlled, a valve orifice in the wall, valve member which can close the valve orifice completely or can open or close it further, a valve stem connected to the valve member, extending on the one side through one of the chambers and outside the housing, being provided with an actuator and extending on the other side into the other chamber and flexible bellows in both chambers, on the one side being connected to the housing and on the other side to the valve stem, whereby the active area of both bellows is equal to or substantially equal to the active area of the valve member, characterized in that only said actuator determines the position of the valve member (8) with respect to the valve orifice (7) and that means are provided for adjusting the position of the valve member (8) with respect to the valve orifice (7) independent on the actuator.

2. Control valve according to claim 1, characterized in that the valve member (8) is adjustably connected to the valve stem (9).

3. Control valve according to claim 1, characterized in that the wall (2) in which the valve orifice (7) is provided is adjustable with respect to the housing (1).

4. Control valve according to claim 1, characterized in that the connecting points of the bellows (12, 13) to the valve stem (10, 9) are adjustable.

5. Control valve according to claim 1, characterized in that the valve stem (9, 10) with the valve member (8) are centered with respect to the valve orifice (7) by one or more slide bearings, one or more leafspring bearings or a combination thereof.

6. Control valve according to one or more of the preceding claims, characterized in that between the valve stem (9) beyond the point where the sealing bellows (13) is connected to the housing (1), and the housing (1) a diaphragm (10) is arranged providing for sealing at rupture or leakage of the bellows.

7. Control valve according to one or more of the preceding claims, characterized in that the actuator is a proportionally acting control magnet.