GB2164125A - Pressure regulating valve - Google Patents

Abstract

An adjustable pressure regulating valve 1 is operated by a fluidics timing circuit 5, so that when the regulating valve is used to supply to a vessel 3 at a controlled rate, the latter rate is substantially independent of the volume of the vessel. <IMAGE>

Description

SPECIFICATION Improvements in and relating to valves Field of the invention This invention relates to process control apparatus. In particular it is concerned with apparatus for pressurising a vessel at a controlled rate.

The prior art There are several ways of pressurising a vessel to a desired pressure at a controlled rate. For example, an operative can do the job essentially manually with the aid of some kind of valve, a pressure gauge and a clock. If the system is carefully calibrated, the rate of pressure build-up can be controlled by the operative opening the valve stepwise over a period of time, say by one turn every two minutes, whilst monitoring the actual pressure gauge to ensure that the actual pressure increase in the vessel does not depart from that expected.

Such manual methods are indeed used, but more commonly an adjustable pressure-reduoing valve in combination with an orifice plate is used. The latter serves to limit the rate at which fluid from a high pressure source passes through the pressure-reducing valve to the vessel which is to be pressurised. This arrangement is essentially automatic in its operation, but it has a fundamental drawback.

The orifice plate (and therefore the whole system) has to be calibrated to suit a particular vessel volume. It is not readily adaptable to different vessels and/or different process conditions. It is also very vulnerable to leakages especially if the orifice is relatively small.

So-called motorised valves are well-known, but the application of motor drive to pressure regulating valves is complicated by the absolute need to avoid over-running and the catasrophic system failure which may result from overstressing the regulator element, usually a diaphragm.

Object of the Invention It is an object of the invention to provide apparatus for pressurising a vessel at a controlled rate which is substantially independant of the volume of the vessel.

Brief discussion of the invention According to the present invention, fluid valve means comprises an adjustable pressure regulating valve connected between a source of fluid at relatively high pressure and a vessel which is to be pressurised, characterised in that the adjustable element of said pressure regulating valve is arranged to be operated by control means comprising a separate fluid valve responsive to a fluidics timing circuit.

Preferably said timing circuit includes a vessel of fixed volume and is operated from a separate, substantially cpmstant pressure fluid source.

The timing circuit may comprise a needle valve which discharges into a separate fixed volume vessel connected only to the separate fluid valve. The latter may be a diaphragm valve whose diaphragm acts directly on the adjustable element of the pressure regulating valve.

Because the timing circuit and the separate fluid valve are essentially independant of the pressure regulating valve itself the control means for the latter is then substantially independant of the volume of the vessel to be pressurised. If for example, a needle valve discharging into a fixed volume is used, the rate of pressure build-up in that volume will depend simply on readily ascertainable factors such as supply pressure, needle valve setting and the fixed volume itself. Once calibrated the setting will clearly be repeatable, unless other parameters are altered. It will be appreciated that the vessel of fixed volume may be a small, closed vessel plus the volume of the fluid circuit of the separate fluid valve, or it may simply be the latter volume on its own.

Because the adjustable element of the pressure regulating valve is controlled by means independant of both the relatively high pressure fluid source and the vessel to be pressurised, the rate of pressurisation of the latter is substantially independant of its volume.

Description of an embodiment of the invention Referring to the accompanying drawing, Figure 1 is a fluidics circuit of valve means in accordance with the invention and Figure 2 is a cross-sectional side view of an adjustable pressure regulating valve modified for use in the circuit just mentioned.

In Fig. 1 an adjustable pressure regulating valve 1 is interposed between a relatively high pressure fluid source 2 and a process vessel 3 which is to be pressurised from the source 2. The adjustable element of this valve is responsive to fluid pressure in a line 4. This pressure is derived from a conventional fluidics timing circuit 5. The latter comprises a neddle valve 6 and a fixed volume 7, together with a one-way valve 8. The needle valve is supplied with fluid by a constant pressure source 9.

The operation of the circuit of Fig. 1 will now be described with the aid of Fig. 2. This latter figure shows the pressure regulating valve 1 in greater detail. The adjustable pressure regulating portion of it comprises a body 10 having a screw threaded inlet and outlet, 11 and 12 respectively. (The inlet is in use connected to the source 2 and the outlet to the vessel 3). Between the inlet and the outlet there is a main valve 13, (shown fully open) spring means 14 biassing the valve 13 towards a closed position in which an annular seal 15 will seat onto a downwardly-facing annular flange 16. A central spindle 17 serves to displace the valve in response to force applied to its upper end by a member 18.The latter is fixed to the central portion of a diaphragm 19, the outer margin of which is clamped to the body 10 by a washer 20 and an upper tubular cap 21 whose purpose and/or structure will be referred to later. A central bore 22 in the member 18 enables the underside of the diaphragm to be vented to atmosphere, via an ancillary bore 23 in the cap 21. However, the free end of the spindle 17 is configured to close the bore 22, as will be discussed later. The tube 26 communicates with the outlet 12 through an aperture 29, so that the pressure in the latter will be applied to the underside of the diaphragm 19.

The member 18 also has an upwardly-facing annular recess which receives one end of a spring 24. This spring is seated at its other end against a plate 25 which is freely slidable inside the cap 21. A central aperture in the plate receives a corresponding by shaped end portion of an actuator rod 27. The latter extends through the upper part of the cap 21, plain bearings 28 being provided within the latter to reduce friction.

The cap 21 also constitutes a support for a separate diaphragm valve 30 the body 31 of which is screwed down onto the correspondingly screw threaded upper part of the cap 21. The actuator rod 27 extends up inside the body 31 and is attached to a diaphragm follower 32 by a screw threaded connection 33.

A return spring 34 is provided to bias the follower against a rubber diaphragm 35. The latter is clamped onto the body 31 by a top closure 36 provided with a screw threaded pipe connection 37. In use this connects directly to line 4 of Fig. 1.

It should be noted that the apparatus of Fig.

2 is shown in the fully-actuated state. That is with the diaphragm 35 displaced as far down as is necessary to fully open the pressure regulating valve below it via actuator rod 27, plate 25 and spring 24 acting against the member 18. The member 18 in turn depresses the spindle 17 against return spring 14 to open the valve 13. It will be appreciated that in the position shown the pressure regulating valve is prevented from functioning since it is held completely open. The opposite extreme is where the valve 13 is fully closed, the tube 26 is open and the pressure in outlet 12 is also applied to the underside of the diaphragm 19. It will be appreciated that for this to happen there must be little or no pressure applied to the diaphragm 35 through line 4.

Considering firstly the normal regulating action of the pressure regulating valve alone, the position of the plate 25 and therefore the degree of compression of the spring 24 determines at what outlet pressure in outlet 12 the pressure differential across the diaphragm 19 will overcome the spring 24 and cause valve 13 to close against the seat 16. Accordingly outlet pressure can be set by selecting the position of plate 25. If the outlet pressure falls below the target value, the valve 13 will open until the outlet pressure rises far enough to close it again. This is the basis of normal pressure regulating action and in conventional use, the plate 25 will be positioned by, say, a handwheel in conjunction with a limit stop effective to present overstressing (bursting) of the diaphragm 19.

However, as used herein the position of the plate 25 is controlled through actuator rod 27 by a separate diaphragm 35. Referring to Fig.

1 again, this diaphragm is operated by a separate timing circuit discharging into an essentially fixed volume. It follows that if the timing circuit is adjusted to permit pressure to build up in that fixed volume over a desired period of, say, minutes, the position of the diaphragm 35 will also reflect that same rate of pressure build-up. It will respond by progressively displacing the actuator rod 27 downwards, compressing the springs 24 and 34. In turn the valve 13 will be progressively opened, permitting fluid to pass from inlet to outlet, but more importantly the outlet pressure at which valve 13 will close is also progressively increased. In other words, the outlet pressure also increases at a progressively increasing rate which is determined by the timing circuit.This rate of outlet pressure increase is not determined by the size of vessel 3 (at least not over a very substantial range of vessel volume). It is a function of the action only of the timing circuit. Thus the object of the invention is achieved.

The apparatus is also very easy to protect against damage. As long as the constant pressure supply to the timing circuit is set at a safe level, the diaphragm 35 cannot be overstressed, thereby preventing accidental overstressing of the pressure regulating valve part of the apparatus. Where air is the working fluid, there is also a high degree of resilient damping so that the risk of damage due to pressure fluctuations in, say, the vessel 3 is minimised.

Unlike a motorised valve, the apparatus need not be complicated by limit switches and/or electronic circuitry. There is relatively little to go wrong and most of the component parts are readily available, off-the-shelf items.

In fact in the example shown in Fig. 2, only the cap 21 and the actuator rod 27 need to be fabricated.

To investigate the effectiveness of the invention, it was used to pressurise a vessel with a small leak.

There was no problem in maintaining a prechosen pressure despite the leak. But on attempting to use a conventional pressure regulator and orifice plate to maintain the same pressure in the same leaking vessel, it was apparent that the conventional arrangement could not cope with even a small leak; the vessel pressure fell steadily during the test period.

Claims (6)

1. Fluid valve means comprising an adjustable pressure regulating valve connected, in use, between a source of fluid at a relatively high pressure and a vessel which is to be pressurised therefrom characterised in that the adjustable element of said pressure regulating valve is arranged to be operated by control means comprising a separate fluid valve responsive to a fluidics timing circuit.

2. Valve means according to claim 1 characterised in that the timing circuit includes a vessel of fixed volume and is operated from a separate, substantially constant pressure fluid source.

3. Valve means according to Claim 2 characterised in that the timing circuit is constituted by a needle valve discharging into a separate fixed volume vessel connected to the separate fluid valve.

4. Valve means according to Claim 2 characterised in that the timing circuit is a needle valve discharging into a vessel of essentially fixed volume constituted by the separate fluid valve itself.

5. Valve means according to any preceding claim wherein the separate fluid valve is a diaphragm valve.

6. Valve means substantially as herein described with reference to and as illustrated by the accompanying drawing.