GB2300733A

GB2300733A - Modulation of Fluid Flow

Info

Publication number: GB2300733A
Application number: GB9508710A
Authority: GB
Inventors: John Henry May; Kieth David Morrigan
Original assignee: PRO AQUA SYSTEMS Ltd
Current assignee: PRO AQUA SYSTEMS Ltd
Priority date: 1995-04-28
Filing date: 1995-04-28
Publication date: 1996-11-13
Also published as: GB9508710D0

Abstract

A fluid pressure modulator (30) for use in a conduit (31) with a pressure reducing valve (10) has barrier means (41) to partially obstruct flow and to create a region of reduced fluid pressure on the downstream side of the barrier, a flow passage from upstream of the barrier to the downstream reduced pressure region and including a venturi (35), fluid flowing through the modulator being returned to the conduit downstream of the barrier. The reduced pressure at the venturi is used to control the pressure reducing valve via a pilot valve.

Description

DESCRIPTION MODULATION OF FLUID FLOW This invention relates to the modulation of flow of a fluid. It is particularly concerned to provide a means of modulating the flow of liquids, especially water. For convenience the invention will be described below with particular reference to water but it will be appreciated that its uses are not to be so limited.

In the supply of water from a source, i.e. mains supply, to a multiplicity of end users, it is conventional practice to pass the supply through a pressure reducing valve, which may, for example, reduce the pressure from a mains pressure of about 70m. to about 40m..

It is desirable that the pressure reducing valve functions to sustain so far as possible a constant outlet pressure regardless of demand and this is normally achieved so far as has proved possible by providing a selfactivating pilot valve to increase flow past the pressure reducing valve as required. The outlet of the pilot valve may be connected to the throat of a venturi downstream of the pressure reducing valve, the venturi being used as part of the modulation system.

It will be appreciated that demand on the water supply varies greatly over any 24 hour period with, usually, relatively low, relatively constant demand overnight and higher demand during the day with peaks and troughs so that maintaining constant pressure to the end user can be difficult, if not impossible to achieve.

Moreover, it will be appreciated that the higher the pressure used, the greater will be the leakage from the system and the greater the wear and tear on the components of the system.

It is an object, therefore, of the present invention to provide an improved means of modulating the flow such that a lower pressure may be utilised on the users' side of a pressure reducing valve while maintaining a more constant pressure supply to the user.

Accordingly, the invention provides a fluid pressure modulator insertable into a fluid supply conduit having a pressure reducing valve, the modulator having barrier means to partially obstruct flow through the conduit whereby a region of reduced fluid pressure is created on the downstream side of the barrier, the modulator providing a flow passage for the fluid from the upstream side of the barrier to the reduced pressure region downstream of the barrier, whereby fluid flows through the modulator including a venturi passage and is returned to the conduit downstream of the obstruction. Preferably the increased flow is returned to the conduit via a passage through the barrier.

In a particularly preferred embodiment the invention provides a fluid pressure modulator comprising a flow chamber having an outer annular flow passage connectable at a first end to a conduit to contain a flow of fluid and closed at its other end, the centre of the chamber comprising a venturi whose inlet is towards the closed end of the annular flow passage and whose outlet is at the first end of the chamber, whereby fluid passing through the chamber travels along the annular passage and then turns to return through the central venturi, the outlet from the venturi passing through a barrier constricting the flow through the conduit.

The barrier preferably is an arcuate disc which blocks off the upper part of the conduit, e.g. pipe, i.e. it provides a cord orifice. The partial constriction encourages flow through the modulator as indicated above.

It will be appreciated that the modulator can be used as a differential flow meter to monitor pressure differentials or, as more specifically described herein, as a pressure modulator with particular applicability to use on the outlet side of a pressure reducing valve in a water supply.

In use with a pressure reducing valve, the modulator of the invention will preferably be coupled to the remote sensing port of a pilot valve, being used to modulate flow at the pressure reducing valve in the conventional manner. This is described in more detail below with reference to the drawings.

The modulator of the invention may be coupled into the system on either the upstream of downstream side of the pressure reducing valve, depending on the particular nature of the system employed and is described below with particular reference to downstream arrangements.

The venturi of the modulator preferably has a relatively long gradually diverging outlet section leading from its throat region to its outlet. By this means, i.e. a shallow angle of outlet passageway, a more efficient diffusion effect is achieved. In other words, a better recovery of pressure is achieved with reduced energy loss.

In conventional systems employing a pilot valve and a venturi on the outlet side of the pressure reducing valve, the modulation signal can be about quadrupled. However, this is achieved at a cost of loss of head pressure and lack of adjustment to the system. It can also happen at peak demand that so much head pressure loss occurs that there is insufficient pressure to some parts of the distribution zone.

(The modulation signal is the difference between the upstream flow pressure and the pressure at the throat of a venturi in the modulation system divided by the net pressure loss, i.e. it is the amplification produced.).

The present invention utilising the described flow chamber can increase the modulation signal (amplification) even further, e.g. up to about eight times the conventional unmodulated system, while suffering little head pressure loss. It can, therefore, enable operation of the fluid supply system at lower overall fluid pressure with the attendant advantages of reduced leakage and increased life of the system.

In another embodiment, the outlet from the flow chamber feeds to another venturi on the downstream side of the barrier. This can increase amplification even further, by a factor of at least ten.

In yet a further embodiment the outlet from the flow chamber feeds into a venturi through a barrier that is suspended centrally in the pipe and whose outer shape is the reverse of that of a venturi, i.e. it is substantially egg-shaped.

In a particularly preferred embodiment, the volume between the closed end of the annular passage in the chamber and the inlet to the venturi is variable, whereby the rate of flow through the modulator is adjustable and controllable. This may be achieved by any convenient means, e.g. by a retractable rod which is connected to the end wall of the chamber whereby the end wall may be moved in or out as required Specific embodiments of the invention will now be further described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a modulator of the invention in position coupled into a mains water supply including a pressure reducing valve; Figure 2 is a sectional view of a modulator according to a first embodiment of the invention; and Figure 3 is a similar view to Figure 2 of a second embodiment of the invention.

In Figure 1, a mains water supply is provided through pipe 31 after passing through a conventional pressure reduction valve 10. Downstream of pressure reduction valve 10 a fluid pressure modulator 30 of the invention is attached to pipe 31 as described in more detail with reference to Figure 2 below.

Pressure reduction valve 10 is coupled to a conventional pilot valve 20 which operates in a conventional manner to increase flow when demand is made on the supply of water. However, the remote sensing port of the pilot valve 20 is connected into the modulator 30 of the invention.

In Figure 2, fluid pressure modulator 30 of the invention is shown attached to water mains pipe 31 downstream of the pressure reducing valve 10 of Figure 1.

Modulator 30 is a tube 32 open at one end where it connects into a corresponding hole 31A in pipe 31 and closed adjacent its other end by a closure 33. Closure 33 is a shaped block as shown forming an end wall.

Tube 32 contains an outer annular flow passage 34, defined between the inner wall of the tube and a centrally-positioned longitudinally-extending venturi 35. The inlet 36 to venturi 35 is adjacent and facing closure 33 of the tube 32. Outlet 37 of the venturi is at hole 31A in the upper surface of pipe 31. A retractable rod 38 is is attached to end wall closure 33. By this means a variable volume 39 at the closed end of tube 32 adjacent the venturi inlet can be provided.

The venturi passageway 37A from its throat 35 to its outlet 37 is relatively long being defined by a shallow angle of about 21/2 to its longitudinal axis.

Outlet 37 of venturi 35 receives a pipe 40 which extends transversely into mains pipe 31 and then turns via a bend 40A to extend as a pipe 40B substantially parallel to the longitudinal axis of pipe 31. Pipe 40B passes through a barrier 41 extending downwardly from the upper surface of pipe 31. Barrier 41 is of arcuate shape and blocks off a little more than the upper half of the diameter of tube 31, i.e. providing a restricted cord orifice. It will be seen, therefore, that the outlet from the venturi 35 via pipe 40, 40B is on the downstream side of barrier 41.

The remote sensing port of pilot valve 20 from the pressure reduction valve circuit is connected at 20A into venturi 35 in its throat region 35A. Thus the pilot valve is controlled by pressure changes in the modulator.

In use barrier 41 constricts flow through mains pipe 31 causing increase in flow rate and drop in pressure.

The drop in pressure on the downstream side of barrier 41 causes water to flow up annular passage 34 of modulator tube 32. At the closed end of tube 32 the water turns to flow into the inlet 36 and through venturi 35. On passing through the throat 35A and to outlet 37 the pressure increases to the outlet.

Simultaneously, the pilot valve 20 of the circuit, which is attached to pressure reducing valve 10 upstream of the modulator valve 30 also functions in its conventional manner by operating in response to normal pressure reductions in pipe 31 due to demand.

The overall flow modulation can be controlled by movement in or out of rod 38 as required.

A further advantage of the system described is that any debris flowing through mains pipe 31 will be towards the bottom inner surface of the pipe and so will not be sucked through the modulator where it might cause blockage.

Figure 3 shows a modification of the modulator 30 of Figure 2.

Pipe 40B passing through barrier 41 outlets into the throat 44 of a second venturi 42 whose inlet end 43 is fitted into a corresponding hole in barrier 41, whereby the amplification effect is further increased.

It will be noted in this embodiment that the pipe 40B discharges fluid parallel to the longitudinal axis of venturi 42. By this means the boundary layer at the throat 44 is not disturbed. (Such disturbance can cause a considerable reduction in the pressure recovery in the expanding outlet section 45 of the venturi.).

It will be appreciated that the invention is not restricted to the embodiments shown. The obstruction 31 or 45 may block off more or less of the pipe as desired. As indicated above, the modulator may be used as a flow meter to monitor differential flow.

Claims

1. A fluid pressure modulator insertable into a fluid supply conduit having a pressure reducing valve, the modulator having barrier means to partially obstruct flow through the conduit whereby a region of reduced pressure can be created on the downstream side of the barrier, the modulator providing a flow passage for the fluid from the upstream side of the barrier to the reduced pressure region downstream of the barrier, whereby fluid can flow through the modulator including a venturi passage and is returned to the conduit downstream of the obstruction.

2. A flow pressure modulator according to Claim 1, in which the increased flow is returned to the conduit via a passage through the barrier.

3. A flow pressure modulator according to Claim 1 or 2, which comprises a flow chamber having an outer annular passage connectable at a first end of the conduit and closed at its other end, the centre of the chamber comprising the venturi whose inlet is towards the closed end of the annular flow passage and whose outlet is at the first end of the chamber, whereby fluid passing through the chamber travels along the annular passage and then turns to return through the venturi, the outlet from the venturi passing through the barrier.

4. A flow pressure modulator according to Claim 1, 2 or 3, in which the barrier is a disc to block off the upper part of the conduit.

5. A flow pressure modulator according to any one of the preceding claims, in which the venturi has a shallow angle of outlet passageway from its throat region to its outlet.

6. A flow pressure modulator according to any one of the preceding claims, in which the outlet from the venturi feeds to a second venturi downstream of the barrier.

7. A flow pressure modulator according to Claim 6, in which the outlet from the first venturi feeds to the second venturi through a barrier suspended centrally in the conduit and whose outer shape is the reverse of a venturi.

8. A flow pressure modulator according to any one of Claims 3 to 7, in which the volume between the closed end of the annular passage in the flow chamber and the inlet to the venturi is variable, whereby the rate of flow through the modulator is adjustable and controllable.

9. A flow pressure modulator according to Claim 8, in which the volume is variable by means of a retractable rod connected to the end wall of the chamber.

10. A fluid conduit comprising a pressure reducing valve and a flow pressure monitor according to any one of the preceding claims.

11. A fluid conduit according to Claim 10, in which the fluid pressure modulator is coupled to a remote sensing port of a pilot valve being used to modulate flow at the pressure reducing valve.

12. A fluid conduit according to Claim 10 or 11, in which the fluid pressure modulator is coupled on the downstream side of the pressure reducing valve.

13. A flow pressure modulator according to Claim 1, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

14. A fluid conduit according to Claim 10, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.