GB2166567A - Pressure reducing valve - Google Patents

Abstract

A pressure reducing valve as described which reduces losses during periods of lower demand and which produces a substantially steady state reduced outlet pressure. A hydraulically operated main valve defines a primary control passage (6) for water passage. A main valve member (7) is mounted to a piston (10) located in an operating chamber (11) which is coupled by a control passage (13) to the inlet and via a control valve (19) to the upstream end (4) of the valve. A control chamber of the control valve (19) contains differential (21) and control (22) diaphragms which are coupled by outlet control passages to the outlet (4) to upstream and downstream sides (28, 29) of a control orifice (30). Regulating valves (35) and an orifice (40) are also provided. <IMAGE>

Description

SPECIFICATION Pressure reducing valve The present invention relates to pressure reducing valves and in particular to pressure reducing valves suitable for use in automatically adjusting pressures in fluid supply pipes subject to variable demand.

It is known that the water supply industry operates with relatively high levels of water loss due, inter alia, to the maintenance of relatively high operating pressures which, whilst sufficient to maintain adequate supply pressure during periods of high demand, become excessive during periods of lower demand. Various attempts have been previously made to reduce such losses by introducing a degree of control over the supply pressure in response to demand. One known system uses electrical circuit means with pressure and flow-rate sensors for monitoring pressure and flow-rate and then processing the information obtained and using it in turn to control suitable electrically operated valve means. Such systems are, however, relatively complex and expensive and require a continuous external power supply giving rise to additional capital and running costs and reliability problems.

It is an object of the present invention to avoid or minimise one or more of the above disadvantages.

The present invention provides a pressure reducing valve suitable for use in a water main, said valve comprising a hydraulically operated main valve having a main valve chamber with inlet and outlet conduit means upstream and downstream respectively of a valve seat and defining a primary control passage, a valve member mounted on a valve centre said member being coupled to a piston movably mounted in an operating cylinder; an operating passage extending from said inlet conduit means to one end of said operating cylinder remote from said valve member; a relief passage connecting said operating passage to an upstream end of a relay valve chamber, and whose downstream end is connected to said outlet conduit means, the relay valve having a valve seat disposed between said upstream end and said downstream end and a movable valve member having a valve stem for engaging said valve seat, said valve stem being provided with a first larger diameter, differential diaphragm and a second smaller diameter control diaphragm, said first and second diaphragm being spaced along said valve stem in respective larger and smaller diameter portions of an operating chamber, first and second control passages connecting said operating chamber on respective first and second sides of said differential diaphragm to the main valve conduit means at respective upstream and downstream sides of a flow orifice defined by a flow restriction means mounted in said outlet conduit means said first side of said differential diaphragm facing in the direction of movement of the relay valve member towards its closed position and facing towards said control diaphragm, said relay valve including a resilient biasing means portioned and arranged for acting on the relay valve member so as to urge said relay valve member towards its open position, said relay valve differential and coupled diaphragm, said first and second control passages, and said resilient biasing means being proportioned and arranged so that, in use when the flow through the valve decreases resulting in decrease of the pressure differential between said first and second control passages of the pressure reducing valve the resultant force on the relay valve stem due to forces from the resilient biasing means and hydraulic pressures acting on the diaphragms urges the relay valve member towards a closed position causing the main valve member to be urged in turn towards its closed position whilst when said flow increases the relay valve member and, in turn, main valve member are urged towards their open positions. Thus with a valve of the present invention the pressure in a water main can be maintained at substantially optimum levels automatically under a variety of demand levels with good reliability and at a relatively economic cost.

Preferably, a differential pressure regulating connection is provided between the first and second control passages, said differential pressure regulating connection being proportioned and arranged for selectively reducing the pressure differential between said first and second control passages. Conveniently said differential pressure comnection includes a continuously variable opening regulating valve.

Preferably, a pressure regulating valve is disposed in said operating passage between said end of said operating cylinder remote from said valve member and said relief passage.

Preferably also a central orifice means is located between said pressure regulating valve and said relief passage.

Further aspects of the invention will become apparent from the following exemplary description of an embodiment illustrated with reference to the accompanying drawing which is a diagrammatic sectional elevation of a valve of the invention suitable for use in a water main.

Reference is now made to the drawing which shows a valve 1 comprising a main valve chamber 2 with respective inlet and outlet conduit means 3 and 4 disposed on either side of a valve seat 5 and defining a primary control passage 6. A main valve member 7 extends slidably across the primary control passage 6 and is formed 8 in conventional manner to provide a progressively variable flow between said valve menber 7 and the primary control passage 6 as the valve mem ber is moved between fully closed and fully open positions (lower and upper positions as viewed in figure 1). The valve member 7 is mounted to the lower end of a valve centre 9 whose upper end is mounted to an operating piston 10 which is in turn slidably mounted in an operating cylinder 11.An indicator rod 12 is sometimes mounted on the other side of the piston 10 to indicate the position of the valve member 7 in known manner.

An operating passage 13 extends from the inlet conduit means 3 to the upper end of the operating cylinder 11 above the piston 10. A relief passage 14 connects the operating passage 13 to the upstream end 15 of a relay valve chamber 16 whose downstream end 17 is connected to the outlet conduit means 4.

The relay valve has a valve seat 18 between the upper and lower ends 15, 17 of the chamber 16 and a needle valve member 19 having a valve stem 20. On the valve stem 20 are mounted a larger diameter, differential diaphragm 21 and above it and spaced therefrom a smaller diameter, control diaphragm 22. The diaphragms 21 and 22 are displacably mounted in respective larger and smaller diameter portions of an operating chamber 23.

First and second control passages 24, 25 connect the operating chamber 23 on first and second sides 26, 27 respectively, of the differential diaphragm 21 with the main valve outlet conduit 4 at upstream and downstream sides 28, 29 of a flow orifice 30 defined in a flow restriction means in the form of an orifice plate 31 mounted in said outlet conduit 4.

The first side 26 of the differential diaphragm 21 is in fact disposed opposite the control diaphragm 22 so that the latter is also subjected to the pressure at the upstream side 28 of the orifice 30 through the first control passage 24, the effective pressure on the control diaphragm 22 will be an upward movement of the needle valve member 19 towards its closed position, and under flow conditions, the effect of different pressures, from the upstream and downstream sides of the flow orifice 30 acting on first and second sides of the differential diaphragm respectively will be a downward movement of the needle valve member 19 towards its open position.

A further downward pressure is applied to the upper end 32 of the valve stem 20 by an axially acting spring 33. The magnitude of the spring force acting on the relay valve stem is pre-set with the aid of an axially moveable screw control means 34 located at the top of the spring.

In order to vary the responsiveness of the relay valve to changes in the flow rate through the main valve, and the resulting pressure differential in the first and second control passages at either side of the flow orifice, said first and second control passages are linked by a connecting passage 38 provided with a continuously variable opening regulating valve 39.

In addition, the various control and operating passages referred to above are provided with suitable regulating valves 35 in known manner. Also a pressure limiting orifice plate 36 is disposed in the primary control passage 13 immediately downstream of a filter means 37 and an additional orifice 40 is located between the regulating valve 35 above cylinder 11 and the operating passage 13. This orifice 40 limits the velocity at which water flows into or out of the cylinder 11. In particular it provides an initial retardation to flow of water into, and out of cylinder 11, giving the regulating valve 35 on top of the cylinder wider control and permitting it to be set further open, reducing the risk of blockage.Also because the response speed of the cylinder is reduced the valve is less susceptible to "hunting" which occurs when reduced outlet pressure continuously rises and falls instead of remaining steady.

The mode of operation of the valve will now be explained with reference to the following example of a typical system which requires a base pressure of 10 metres but due to flow range requires 25 metres at a velocity of 2.5m/s. The base outlet pressure of 10 metres is first obtained by adjusting the relay valve spring load under minimum flow conditions. The relay valve is then tuned to give a 15 metre progressive pressure rise as flow increases up to the maximum of 2.5m/s. With the desired base outlet pressure set within the range of the relay valve spring, and the regulating valves set approximately, the main valve automatically adjusts itself to maintain the tuned downstream pressure range.

This is achieved by the interaction of four pressures: P1-The inlet pressure P2-The outlet pressure P3-The intermediate pressure, which is produced by the relay system and acts on the upper side of the main valve piston.

P4-The downstream pressure The relay valve, basically an adjustable orifice, is actuated by pressure acting on the control and differential diaphragms and is subjected to a constant spring load from above. The underside of the control diaphragm is connected to the valve outlet pressure P2, and top and bottom sides of the large diaphragm are connected, respectively, to the outlet pressure P2 and the downstream pressure P4. The differential between P2 and P4 is created by the orifice plate and provides a downward force on the relay valve which is related to the rate of flow. Movement of the relay valve and consequently the main valve position is therefore governed by the spring load, rate of flow and by the pressure immediately downstream of the valve.

At the base pressure setting, the spring force is balanced by the pressure acting on the two diaphragms, an increase in the flow rate produces a differential load on the differential diaphragm which opens the relay valve so that P3 decreases, the main valve opens further and the downstream pressure increases.

As flow decreases, the differential load diminishes, the relay valve tends to close, allowing pressure P3 to increase, causing the main valve to tend to close, thus reducing the downstream pressure.

If, at maximum flow, the pressure increase achieved is greater than that required its magnitude can be reduced by partially opening the differential regulating valve which connects the two sides of the differential diaphragm and thus regulates the differential pressure across this diaphragm.

It will be appreciated that various modifications may be made to the pressure reducing valve hereinbefore described without departing from the scope of the invention. For example, the orifice 40 can be omitted and flow into and out of the cylinder 11 reduced to minimise hunting by almost closing the regulating valve 35. However, when the valve is adjusted there is a slight probability that it will be blocked by small particles which are not removed by the filter 37 and an improved filtering system could be used in this case.

Also, the spring could be replaced by any other suitable resilient adjusting means such as a spring diaphragm.

Advantages of the apparatus hereinbefore described are that water losses during periods of lower demand are minimised and hunting is minimised to maintain the reduced outlet pressure substantially steady.

Claims (6)

1. A pressure reducing valve suitable for use in a water main, said valve comprising a hydraulically operated main valve having a main valve chamber with inlet and outlet con duit means upstream and downstream respectively of a valve seat and defining a primary control passage, a valve member mounted on a valve centre, said member being coupled to a piston movably mounted in an operating cyl inder; an operating passage extending from said inlet conduit means to one end of said operating cylinder remote from said valve member; a relief passage connecting said op erating passage to an upstream end of a relay valve chamber, and whose downstream end is connected to said outlet conduit means, the relay valve having a valve seat disposed be tween said upstream end and said down stream end and a movable valve member hav ing a valve stem for engaging said valve seat, said valve stem being provided with a first larger diameter, differential diaphragm and a second smaller diameter control diaphragm, said first and second diaphragm being spaced along said valve stem in respective larger and smaller diameter portions of an operating chamber, first and second control passages connecting said operating chamber on respective first and second sides of said differential diaphragm to the main valve conduit means at respective upstream and downstream sides of a flow orifice defined by a flow restriction means mounted in said outlet conduit means, said first side of said differential diaphragm facing in the direction of movement of the relay valve member towards its closed position and facing towards said control diaphragm, said relay valve including a resilient biasing means portioned and arranged for acting on the relay valve member so as to urge said relay valve member towards its open position, said relay valve differential and control diaphragm, said first and second control passages, and said resilient biasing means being proportioned and arranged so that, in use, when the flow through the valve decreases resulting in decrease of the pressure differential between said first and second control passages of the pressure reducing valve, the resultant force on the relay valve stem due to forces from the resilient biasing means and hydraulic pressures acting on the diaphragms urges the relay valve member towards a closed position causing the main valve member to be urged in turn towards its closed position, whilst when said flow increases the relay valve member and, in turn, main valve member are urged towards their open positions.

2. A pressure reducing valve as claimed in claim 1 including differential pressure regulating means disposed between said first and second passages, said differential pressure regulating connection being proportioned and ar ranged for selectively reducing the pressure differential between said first and second con trol passages.

3. A pressure reducing valve as claimed in claim 2 where said differential pressure con nection includes a continuously variable open ing regulating valve.

4. A pressure regulating valve as claimed in any preceding claim wherein a pressure regu lating valve is disposed in said operating pas sage between said end of said operating cylin der remote from said valve member and said relief passage.

5. A pressure regulating valve as claimed in claim 4 wherein a control orifice means is lo cated between said pressure regulating valve and said relief passage.

6. A pressure regulating valve substantially as hereinbefore described with reference to the accompanying drawing.