GB2256508A

GB2256508A - Pressure control apparatus

Info

Publication number: GB2256508A
Application number: GB9212244A
Authority: GB
Inventors: Dieter A Hofmann; Jarek Rosinski; Stuart John Twidale
Original assignee: Walter Frank & Sons Ltd
Current assignee: Walter Frank & Sons Ltd
Priority date: 1991-06-08
Filing date: 1992-06-08
Publication date: 1992-12-09
Also published as: GB9112342D0; GB9212244D0

Abstract

Pressure control apparatus comprises a valve housing having an inlet 2 and an outlet 3 and accommodating a main valve and a pilot valve 22 associated with the main valve and adapted to be set at the pressure required at the outlet 3. The pilot valve maintains the main valve open whilst pressure at the outlet is below the pre-set pressure of the pilot valve and causes a partial closing of the main valve when the pressure at the outlet equals or exceeds the pre-set pressure. The valve head 7 of the main valve includes a restricted orifice 16 which connects the control chamber 5 of the main valve with the inlet 2. The orifice 6 is protected by a filter 17. <IMAGE>

Description

PRESSURE CONTROL MEANS This invention relates to pressure control means.

There are numerous applications where fluid needs to be dispensed or distributed at a constant required pressure and where the source of supply can be subjected to pressure variations. This is particularly significant in fire fighting where the hose pressure is most desirably at a constant required pressure, and it is well known that both mains and auxiliary sources of supply are frequently subjected to pressure variations.

In an attempt to overcome this difficulty, it is known to provide a pressure regulating valve. In one form of construction a spring loaded balance pressure reducing valve is combined with a hydrant stop valve. The reducing valve element is opened by the load applied to the pressure adjusting spring and closed by the outlet (hose) reduced pressure acting upon the underside of the low pressure seal.

Under working conditions, the balance of these two forces determines the degree of valve opening required to maintain a steady outlet pressure, irrespective of changes in the flowrate. In another form of construction a piston is provided on a stem running through a piston chamber pressurised by the hose water. The pressure on the piston is counterbalanced by a spring within a spring chamber acting on the stem via the spring nut and washer. At those pressures below the 'set' pressure the spring force exceeds that on the piston, thus holding the valve open. As the hose pressure exceeds the 'set' pressure the force on the piston overcomes that of the spring, thereby throttling the valve to the point where the piston and spring forces balance at the 'set' pressure.

Both types of pressure regulating hydrant valves are direct control valves where the valve is opened or closed by the load applied to the pressure adjusting spring. This, however, requires the use of a strong spring for which a change in valve position would result in negligible change in the spring force. This normally leads to a spring of large overall dimensions.

It is the objective of the present invention to provide a pressure control means that overcomes those disadvantages mentioned above.

According to the present invention, a pressure control means comprises a main valve between the inlet to the control means and the outlet from the control means and a pilot valve, associated with the main valve, and adapted to be set at the pressure required at the outlet from the pressure control means, said pilot valve maintaining said main valve open whilst pressure at the outlet is below the pre-set pressure of the pilot valve, and said pilot valve causing a partial closing of the main valve when the pressure at the outlet equals or exceeds the pre-set pressure at the control valve.

The pilot valve may be such that it is pre-set at the required pressure, but preferably is provided with a means of adjustment and whereby its pressure setting can be varied to suit different requirements.

Preferably both of the main valve and the pilot valve are spring-loaded, but the employment of a pilot valve avoids the need for the main valve spring to overcome the pressure at the inlet, and consequently, much lighter and more sensitive springs can be employed than has hitherto been possible.

Thus, the pilot valve can be located at the outlet from the pressure control means, or in a chamber connected to the outlet, and whereby the pilot valve is acted on from below by the pressure at the outlet, the pilot valve lying in a pilot valve chamber communicating with the outlet or the chamber associated with the outlet to one side of the pilot, and to the other side of the pilot valve, the pilot valve chamber communicating with a main valve chamber and in which the main valve is slidably mounted, there being a restricted access provided through the main valve to communicate the inlet to the control means with the main valve chamber.

With pressure water supplied to the inlet to the control means, the main valve is opened against its spring, to enable pressure water to pass through the outlet. At the same time, pressure water passes through the restricted access to the main valve chamber from where it passes to the pilot valve chamber. With the pressure in the outlet below the preset pressure of the pilot valve, the pilot valve remains open, and water is allowed to pass through the pilot valve chamber and back to the outlet or the chamber associated with the outlet. In the event of a pressure build up at the outlet from the pressure control means, the pilot valve is acted on to close the pilot valve as the outlet pressure reaches the preset pilot valve pressure and closure of the pilot valve prevents water from the main valve chamber from passing through the pilot valve chamber.As a consquence, there is a build up of pressure in the main valve chamber to counterbalance the pressure on the main valve from the inlet, and enabling the light main valve spring to partially close the main valve. As the pressure at the outlet falls, the pressure below the pilot valve falls until the pressure at the outlet is below the preset pilot pressure, and when the pilot valve opens to relieve the pressure in the main valve chamber, and hence enable the main valve to open further under the action of the pressure at the inlet.

By using a pilot valve acted on by the outlet presure, there is the immediate sensing and reaction to a build up of pressure at the outlet when it reaches a predetermined maximum, and as a result, the pressure at the outlet can be maintained constant with a considerably greater degree of certainty, and without the need for heavy springs, than has hitherto been possible.

The restricted access to the main valve chamber may simply be a small diameter orifice through the main valve head, and preferably said orifice is overlaid by a filter.

Alternatively, a sintered filter tube may be provided secured in a bore in the main valve head, with a restricted passageway extending from the end of the bore and to the chamber. Such a construction has the additional advantage that the tube can serve additionally as a guide tube during movement of the main valve head.

One embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation of one embodiment of pressure control means according to the present invention with the pilot valve in the open position; and Figure 2 corresponds to Figure 1 but shows the pilot valve in the closed position and the main valve in a throttled position.

In the drawings a pressure control means has a valve body 1 with an inlet 2 for connection to a mains or auxiliary source of supply of water, and an outlet 3 for connection, eg., to a hose. Within the body, between the inlet and the outlet is a chamber 4 into which extends a bore 5 forming a main valve chamber, co-axial with the inlet 2, there being a cylinder 6 forming a main valve head slidably mounted in the bore and closed at its end 7 towards the inlet. Within the cylinder a guide stud 8 is provided, to engage the bore of a projection 9 from a pusher 10, a compression spring 11 being provided and extending between a shoulder on the pusher 10 and the closed end 7 of the cylinder. At the opposite end of the bore 5 a cup nut 12 is provided, through which extends the threaded sector 13 of a stem 14 on which a hand wheel 15 is provided, the stem terminating in a bearing member engaging with the pusher 10. In the absence of pressure water at the inlet 2, the spring 11 urges the cylinder 6 out of the bore and into engagement with the inlet, and the hand wheel can be rotated to vary the compression of the spring to set a pressure required to open the inlet 2 at the pressure required at the outlet 3.

In the end face of the cylinder 6, a bleed hole 16 is provided, overlaid by a filter 17, to connect the chamber 4 to the bore 5, and in the bore 5, a passageway 18 is provided, connecting the bore to a pilot valve chamber 19 at one side of a valve seat 20, the pilot valve chamber having a passageway 21 connecting the chamber 19 to the opposite side of the valve seat to the chamber 4. A pilot valve 22 has a head 23 to engage the valve seat 20, and a tail 24 extending down a bore 25, connecting the pilot valve chamber to the chamber 4. To the opposite side, the pilot valve head is connected by a stem 26 to a control compression spring 27 located between a head 28 on the stem 26 and the closed end of a bore 29 in a pilot cup 30.

To ensure the absence of leakage past the cylinder 6 and the pilot valve 22, respective elastomeric seals 31 and 32, are provided and whereby a greater consistency of performance can be assured.

At the onset of operations and with the spring 11 preset, and the spring 27 selected, in accordance with a pressure required eg., in a hose connected to the outlet 3, pressure water is admitted to the inlet, to lift the cylinder from the inlet, and allow water to flow through the outlet at the required rate. At the same time, water passes through the bleed hole 16 to fill the bore 5, water flowing from the bore to the pilot valve chamber 19, from where it flows through the passageway 21 and back to the chamber 4.

This condition remains for so long as the pressure, eg., in a hose secured to the outlet is at or below a required pressure. Should for any reason, pressure build up beyond the outlet, the pressure in the chamber 4 rises and acts on the tail 24 of the pilot valve to close the pilot valve head on to its seat 20. Consequently, water can no longer flow from the bore 5 to the chamber 4, and a pressure build-up occurs in the water in the bore until it equates to the pressure in the chamber 4. Once pressure equilibrium is reached, the spring 11 urges the cylinder 6 towards the inlet to throttle the supply of water to the outlet, hence reducing the pressure at the outlet, and when reduced to the predetermined pressure, the pilot valve 22 re-opens to relieve the pressure from within the bore 5.

It will therefore be understood that by using a pilot valve acted on by the outlet pressure, and the employment of the pilot valve to cause a build up of pressure in the bore and to act on the cylinder, there is the immediate sensing and reaction to a build-up of pressure, allowing the maintenance of constant pressure at the outlet without the need for heavy springs.

Claims

1. A pressure control means comprising a main valve between the inlet to the control means and the outlet from the control means and a pilot valve, associated with the main valve and adapted to be set at the pressure required at the outlet from the pressure control means, said pilot valve maintaining said main valve open whilst pressure at the outlet is below the pre-set pressure of the pilot valve, and said pilot valve causing a partial closing of the main valve when the pressure at the outlet equals or exceeds the pre-set pressure at the control valve.

2. A pressure control means as in Claim 1, wherein the pilot valve is pre-set at the required pressure.

3. A pressure control means as in Claim 1, wherein the pilot valve has a means of adjusting the pressure setting to enable variation to suit different requirements.

4. A pressure control means as in any of Claims 1 to 3, wherein the main valve is spring-loaded towards a closed position and the pilot valve is spring-loaded towards an open position.

5. A pressure control means as in any of Claims 1 to 4, wherein the pilot valve is located at the outlet from the pressure control means.

6. A pressure control means as in any of Claims 1 to 4, wherein the pilot valve is located in a chamber connected to the outlet from the pressure control means.

7. A pressure control means as in any of Claims 1 to 6, wherein the pilot valve lies in a pilot valve chamber communicating either with the outlet from the pressure control means or a chamber associated therewith, there being a valve seat in the pilot chamber, and there being a connection between the pilot valve chamber and a main valve chamber to one side of the valve seat and a connection between the pilot valve chamber and either the outlet from the pressure control means or the chamber associated therewith, to the other side of the valve seat, the main valve chamber communicating with the inlet to the pressure control means by way of a restricted access.

8. A pressure control means as in Claim 7, wherein the restricted access to the main valve chamber is provided by a small diameter orifice through a main valve head slidably mounted in the valve chamber, said orifice being overlaid by a filter.

9. A pressure control means as in Claim 7, wherein the restricted access to the main valve chamber is provided by a sintered filter tube lying in a bore in a main valve head slidably mounted in the main valve chamber, there being a restricted passageway extending from the end of the bore to the chamber.

10. A pressure control means as in Claim 9, wherein the sintered filter tube serves as a guide tube during movement of the main valve head.

11. A pressure control means substantially as hereinbefore described with reference to the accompanying drawings.