GB2079983A

GB2079983A - Pilot operated control valve

Info

Publication number: GB2079983A
Application number: GB8120301A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-07-02
Filing date: 1981-07-01
Publication date: 1982-01-27
Also published as: DK146637B; GB2079983B; DK146637C; DE3125605A1; DK286180A; DE3125605C2

Abstract

A control valve for controlling fluid flow, comprising a pilot valve (19) which is operable by hand, thermostat, pressostate or otherwise and whose opening serves to reduce the pressure in a control chamber (18), which communicates with the control valve inlet side (2) through a partly closed opening containing a readily replaceable control member (29). The pressure in the control chamber (18) affects, through a diaphragm or bellows, the main valve 6 of the control valve which is increasingly opened when the pressure in the control chamber (18) decreases. The valve spindle (20) and the valve disc (21) of the pilot valve (19) and the control member (29) have a common axis and form a coherent unit during the entire controlling course, said parts being either interconnected or engaged with each other by the force of a pressure spring (31) interposed between the control member (29) and the valve spindle (5) of the main valve member. Thus, the valve characteristic of the control valve may be changed as desired by replacing just the valve disc (21) of the pilot valve, and the proportional band of the control valve may be changed merely by replacing the control member (29). <IMAGE>

Description

SPECIFICATION A control valve The invention relates to a control valve for controlling fluid flow through a main valve member disposed between the inlet side and outlet side of the control valve, which contains at least one pilot valve which connects the inlet side to the outlet side via a control chamber, the connection between the control chamber and the inlet side being formed by an opening in a movable wall in the control chamber, said opening being partly closed by a control member which is movable in the opening and partly formed so that the opening is partly open in the closed position of the pilot valve and is continuously reduced by the opening of the pilot valve until the pressure in the control chamber is smaller than the pressure in the intermediate chamber, and partly formed so that the resulting cross sectional area between the opening and the control member varies with the position of the control member in the opening, said position being controlled by the pressure in the control chamber so that said cross sectional area increases when the pressure in the control chamber decreases because of the opening of the pilot valve and vice versa, said movable wall being secured to the valve spindle of the main valve member.

The pilot valve of the control valve may of course be operated manually, but in ordinary uses the pilot valve is controlled by the temperature of the pressure on a representative location in the circuit which the control valve forms part of, by means of a thermostat or pressostate.

In control valves of the present type it is endeavoured to adapted the temperature range or proportional bands between fully open and fully closed ventil to the dynamic conditions of the control circuit to optimize control accuracy without creating fluctuations in the system.

It is known, e.g. from the German Patents Nos.

260 137, 262 224, and 270 220, to construct a control valve, which may be controlled by a pilot valve, by means of a control member which is firmly incorporated in the main valve and whose contour determines the valve characteristic of the valve, the valve characteristic being the relative flow through the valve as a function of the relative opening of the pilot valve at a pressure drop across the valve of 1 Kp per cm2.It is also known that the slit around the control member, which is necessary for reasons of manufacture and operation, causes the main valve to close abruptly when the opening of the pilot valve is below the critical value where the flow through the pilot valve is smaller than the flow through the slit area around the control member; this causes a discontinuous jump in the valve characteristic of the valve at this critical degree of opening, and the valve is accordingly unsuitable as a control valve.

For control purposes proper, it has therefore previously been necessary to use valves which are controlled directly by a thermostat or pressostate.

This means the the whole valve or its characteristic determining valve disc must be replaced if a control valve of another valve characteristic is to be used. Similarly, the whole thermostat or the pressostate has to be replaced if a control valve with another proportional band is desired. Also, it is necessary to use a thermostate or pressostate of great closing force when the valve has a large flow are and/or when the pressure drop across the valve is great.

The object of the invention is to eliminate the discontinuity in the valve characteristic of a pilot controlled valve so that the valve together with a thermostat or pressostate may be used as a control whose control curve or proportional band can readily be changed by replacing simple and readily accessible parts. Further, the same pilot valve may be used for all valve sizes and thus the same thermostat or pressostate for all valve sizes irrespective of difference in pressure across the valve.

This is achieved according to the invention in that the control valve is so constructed that the valve spindle and the valve disc of the pilot valve and the control member have a common axis and form a coherent unit during the entire controlling course. As the valve disc of the pilot valve and the control member have the same axis and are axially retained with respect to each other, the control member may be controlled in a well-defined manner in relation to the control opening such that the control opening is partly open when the pilot valve is closed, and so that initial opening of the pilot valve causes initial closing of the control opening until there is the same fluid flow through the pilot valve and the control opening; then the valve body is moved to a position of equilibrium where the fluid flow through the control opening and the pilot valve is the same, thereby obviating discontinuous movement of the valve body. The proportional band of the control valve may easily be changed by replacing the control member, and the valve characteristic of the control valve may easily be changed by replacing the valve disc or cone of the pilot valve, said disc or cone being the same for all control valve sizes so that the intended control properties are obtained in the entire working area.

When the valve spindle and disc of the pilot valve are connected to the control member, said valve spindle and disc and control member form a common coherent element.

In a preferred embodiment of the invention the control member is kept engaged with the valve disc of the pilot valve by the force of a pressure spring interposed between the control member and the valve spindle of the main valve member.

This provides for replacement of the control member independently of replacement of pilot valve, and vice versa. The stated pressure spring also serves to keept the moving parts in welldefined relative positions during the entire controlling course.

The invention will be described more fully below with reference to the drawings, in which Fig. 1 shows a longitudinal section of a first embodiment of a control valve according to the invention in a closed position, Fig. 2 shows a longitudinal section of the control valve of Fig. 1 in a partly open position, Fig. 3 shows a longitudinal section of a second embodiment of a control valve according to the invention in a closed position, and Fig. 4 shows a longitudinal section of the control valve of Fig. 3 in a partly open position.

The control valve shown in Figs. 1 and 2 has a valve housing 1 with an inlet side 2 and an outlet side 3 for a fluid flow passing through the main valve member of the control valve; the main valve member is composed of a valve seat 4 secured in the valve housing 1 and a valve cone 6 secured on a valve spindle 5. The main valve member is shown in a closed position in Fig. 1 and in open position in Fig. 2.

The valve housing 1 has a guide sleeve 7 for the valve spindle 5 of the main valve, said spindle 5 having a plurality of annularly spaced openings or holes 9 that connect the inlet side 2 to the interior of the valve spindle 5. The valve spindle 5 has moreover a plurality of annularly spaced openings or holes 10 connecting its interior 8 to an intermediate chamber 11 whose top is closed by an actuator housing 12 by means of a gasket 13.

A piston plate 14, which does not fit tightly against the sides of the intermediate chamber 11 and has a greater area than the valve cone 6, is perpendicularly secured on the valve spindle 5 by means of a nut 15.

The edge of the piston plate 14 is connected to a projection, concentric with the edge, on the lower portion of the actuator housing 12 by means of a partly airtight bellows 17, whose interior constitutes a control chamber 18.

The actuator housing has screwed into it a pilot valve 1 9 which has a valve spindle 20, a valve disc or valve cone 21 and a valve seat 22. The valve spindle 20 is surrounded by a pressure spring 23 and an airtight bellows 23, which is surrounded by a hydraulic pressure transmitting medium 25 that may be fed from a hydraulic pipe 26. The pilot valve has a channel 27 which, through another channel 28 in the housing 1, communicates with the outlet side 3 of the control valve.

The valve spindle 5 of the main valve contains a control member 29 which is concentric with the spindle and has a conical upwardly tapering contour protruding through and forming a closure for an opening 30 in the nut 15, which constitutes the movable wall of the control chamber 18. A pressure spring 31 keeps the upper end 32 of the control member in engagement with the valve disc 21 of the pilot valve by the force of the spring. The control member 29, which is concentrically fitted in the valve seat 5 of the main valve, is also concentric with the valve spindle 20 and the valve disc 21 of the pilot valve 19.

Instead of the bellows 17, the piston plate 14 might be formed as an essentially tightly fitting piston in the intermediate chamber 11 or be surrounded by a diaphragm sealing engaged with the wall of the intermediate chamber.

The valve spindle 20 and the valve disc 21 of the pilot valve might be manufactured integrally with the control member 29, thereby making it possible to omit the pressure spring 31.

The control valve shown in Fig. 1 operates in the following manner: When the control valve is in the position shown in Fig. 1 no fluid can flow from the inlet side 2 to the outlet side 3; on the contrary, the same pressure will be built-up in the control chamber 1;8 as on the inlet side 2 of the control valve as a consequence of the pressure fluid being forced from the inlet side 2 through the holes 9 into theF control chamber 18 via the opening 30, which is kept partly open because the control member 29 is urged away from the opening 30 by the valve disc 21.Thus, the same pressure is established in the control chamber 1 8 and in the inlet side 2, and as the pressure in the outlet side 3 is smaller than the pressure in the inlet side 2 the resulting force on the valve spindle 5 causes the valve cone 6 to be urged against the valve seat 4 so that the main valve will remain closed.

The control valve is opened by means of the pilot valve 19, the pressure in the hydraulic fluid 25 around the bellows 24 being lowered so that the pressure spring 23 may lift the valve spindle 20 and the valve disc 21 from the seat 22. Then fluid may flow from the control chamber 1 8 through the pilot valve 22 to the outlet side 3, and the control member 29 is simultaneously lifted by the spring 31, thereby causing the flow area through the opening 30 to be reduced continuously with the travel of the valve spindle 20 until the fluid flow through the opening 30 becomes smaller than the fluid flow through the opening between the pilot valve seat 22 and the disc 21 in the pilot valve 19.When the fluid flow through the opening 30 becomes smaller than the fluid flow through the pilot valve 19, the pressure in the control chamber 18 decreases, and the piston plate 14 with the valve spindle 5 and the valve cone 6 therefore moves to a position of equilibrium where the fluid flow through the opening 30 is the same as through the pilot valve 19, and fluid is simultaneously allowed to flow through the main valve member through the area, between the valve seat 4 and the valve cone 6.

If another valve characteristic is desired, the valve cone of the pilot valve can just be replaced by another valve cone whose conical portion is ground differently, corresponding to the desired characteristic.

If, on the other hand, another proportional band is desired, the control member 29 may be replaced by another control member whose conical portion has another cone angle.

Fig. 2 shows, as mentioned, the valve of Fig. 1 in a partly closed position. If the bellows 17 in the control valve shown in Figs. 1 and 2 leaks, the pressure in the control chamber 1 8 will increase because the full feeding pressure surrounds the bellows 17 via the holes 10. This means that the control valve automatically moves towards the closed position. This ensures that no unintentional states may arise as a consequence of defects in the bellows 1 7.

Figs. 3 and 4 show a second embodiment of the-control valve according to the invention, shown in a closed and an open position, respectively. Here, the corresponding parts have been given the same reference numerals as in Figs. 1 and 2, but are primed.

The control valve shown in Figs. 3 and 4 differs from the control valve shown in Figs 1 and 2 essentially only in that the inlet pressure on the inlet side 2' of the valve acts on the underside of the valve cone 6' of the main valve member. The intermediate chamber 11' is in this embodiment arranged between the channels 27' and 28' and therefore communicates with the outlet side 3' of the control valve and not its inlet side as in the embodiment shown in Figs. 1 and 2. Therefore, unintentional openings in the bellows 17' in the embodiment shown in Figs. 3 and 4 cause the pressure in the control chamber 18' to decrease when fluid flows from the control chamber 18' through said holes in the bellows 17' to the outlet side 3'.This will additionally open the control valve, which means that this embodiment has a less advantageous performance when such a defect occurs than the embodiment shown in Figs. 1 and 2. Also, it should be mentioned that the control chamber 18' in the second embodiment must be absolutely tight so that the only fluid flow from this control chamber 18' takes place in a controlled manner through the pilot valve 19'.

The present control valve is a closing valve as the main valve closes when the pressure in the hydraulic fluid 25 increases, and the valve spindle of the pilot valve 1 9 is therefore pushed downwards to close the pilot valve 19. However, the control valve can easily be changed from a closing valve to an opening valve, merely by changing the conical shape of the pilot valve 1 9 so that the flow through the pilot valve is increased when the pressure in the hydraulic fluid 25 increases and the valve spindle 20 is forced forwards.

Claims

1. A control valve for controlling fluid flow through a main valve member disposed between the inlet side (2, 2') and outlet side (3, 3') of the control valve, which contains at least one pilot valve (19, 19') which connects the inlet side (2, 2') to the outlet side (3, 3') via a control chamber (18, 18'), the connection between the control chamber (18, 18') and the inlet side (2, 2') being formed by an opening (30, 30') in a movable wall (14, 14') in the control chamber (18, 18'), said opening (30, 30') being partly closed by a control member (29, 29') which is movable in the opening (30, 30') and partly formed so that the opening (30, 30') is partly open in the closed position of the pilot valve (1 9, 19') and is continuously reduced by the opening of the pilot valve (19, 19') until the pressure in the control chamber (18, 18') is smaller than the pressure in the intermediate chamber (11, '), and partly formed so that the resulting cross sectional area between the opening (30, 30') and the control member (29, 29') varies with the position of the control member (29, 29') in the opening (30, 30'), said position being controlled by the pressure in the control chamber (18, 18') so that said cross sectional area increases when the pressure in the control chamber (18, 18') decreases because of the opening of the pilot valve (19, 19') and vice versa, said movable wall (14, 14') being secured to the valve spindle (5, 5') of the main valve member characterized in that the valve spindle (20, 20r) and the valve disc (21, ') of the pilot valve (19, 19') and the control member (29,29') have a common axis and form a coherent unit during the entire controlling course.

2. A control valve according to claim 1, characterized in that the valve spindle (20, 20') and the valve disc (21, ') of the pilot valve (19, 19') are connected to the control member (29, 29').

3. A control valve according to claim 1, characterized in that the control member (29, 29') is kept engaged with the valve disc (21, ') of the pilot valve (19,19') by the force of a pressure spring (31, 31') interposed between the control member (29, 29') and the valve spindle (5, 5') of the main valve member.