PILOT VALVE

Abstract: There is provided a pilot valve (50), suitable for use in water and gas supply systems, the valve including biassing means (57), to control a gate (55), for controlling fluid flow through a control chamber (51), and a second chamber (52), which is sealed by a diaphragm (53), the second chamber (52), in use, receiving a control pressure for controlling the operation of the gate (55), such that an increase in control pressure acts to reduce fluid flow through the gate (55). The side of the diaphragm (53), against which the control pressure is not applied, is in fluid communication with the control chamber (51).

Description: P I LOT VALVE The present invention relates to a pilot valve, for example of the type which is commonly used to control a pressure reducing valve in water and gas supply systems. Figure 1 illustrates the use of a "sincle chamber" pilot valve 1 to control a pressure reducing valve (PP.V - shown schematically as item 2) _3 commonly U3ed in a water supply system, in the context of a gas supply system such a pressure reducing valve is normally known as a "regulator" or "governor", but herein the single term "?RV" is used for simplicity as referring to both types of system. The fluid to be controlled (usually water or g s, and m this example will be taken tc be water) flows along the main pipe 3 through the PRV, The outlet pressure (Po) is usually less than the. inlet-, pressnrp. (Pi) ci _ t _ 1-h<=> action of the PRV. The amount ot pressure reduction is controlled by operation of the PRV under control of pilot valve 1. An auxiliary flow pipe 4 carries water from the inlet of the PRV to the control chamber 5 of the pilot valve 1 and then back to the outlet of the FRV. Prior to entering the control chamber 5, the water passes through _ venturi chamber (or primary orifice) 6 or, more correctly in the cor-teκt of a gas supply system, an inspirator 6 and the water pressure (Pv) at the outlet side 7 zi the chamber or inspirator controls the PRV. The flow of water through the control chamber 5 is controlled by a gate mechanism 6 which is linked to a diaphragm 9. A spring 10 applies force to the rear of the diaphragm 9 and the amount of force sup lie by the spring may bft varied by an ad ustment screw 11.- In a steady state situation (where Po remains constant) the water pressure m the control chamber 5 will be balanced by the force generated the spring and the gate 8 will remain in a constant position. Thus the flow through the auxiliary pipe 4 will remain constant and ?V will remain constant. If the control pressure (Po) fails, the spring 10 causes the yaLe 8 Lυ open further and the flow through the auxiliary pipe increases. Accordingly, the flow through the venturi 6 also increases which results in pressure Pv decreasing, causing the PRV to open further. This results in the control pressure Po rising again and the system should then reach a steady state again at the previously set value of Po. ϊn order to provide an improved control sys em, the μiea-i.t applicant _s already disclσs-sd _ system which uses a "dual chamber" pilot va-.ve m European Patent No. 574241. Figure 2 shows an example of a system utilising a "sandwich plate" dual chamber pilot 20. The pilot valve 20 performs the same general function in the control system as the pilot valve of Figure 1 but m this example the a justment previously provided by adjustment screw 11 is effectively supplemented by an adjustment using a control pressure (Pc) - As further relevant background art may be mentioned the gas supply pressure: control a aia-αt. as disclosed by the present applicant m 3B-A-2-.j-.e48. The pilot valve 20 includes a second chamber 21 which is effectively divided into two portions 22 and 23 by a wall 24. The control pressure Pc effectively acts against the force of spring 10 by virtue of diaphragm 26. As with Fiqure 1, the soring is mechanically connected by arm 28 to a gate ιr-ecb?m sr 8 which performs the same function as previously. The arm 28 paαcea through wall 24 and the aperture through which it passes is sealed by a seal 29 so that chamber 23 does not contain any water but instead is vented to the atmosphere. If the control pressure Fc remains constant, then the system operates as explained with reference to Figure 1. However, f the control pressure Pc is reduced then the gate 8 will open further thereby reducing pressure Pv and increasing the outlet rcεsure P . This is usually referred to as a "failsafe" system since in the event that the control pressure fails i.e. fails to 2ero, the outlet pressure Po will bε set to its maximum value. Figure 3 illustrates an alternative but mechanically equivalent "dual chamber" pilot valve arrangement tc that sh w in F gu ? . The arrang men of Figυrp. 3 is sometimes referred to c "p noo c adapted" pilot. In this arrangement, the second chamber 31 is located SL the base of the pilot 30. As with the arrangement of Figure 2, the second chamber 31 is divided by a diaphragm 34 into two chambers 32 and 33 and the control pressure Pc is applied to chamber 32. The diaphragm 34 is mechanically linked via an arm 35 to the gate mechanism 8 but is not rigidly limited to the gate or spring. The arm 35 presses into r.ontrnl r.hn ber 5 via an aperture which is again σeαlcd with seal 36. In the e Pociment or Figure ά , the control pressure Pc again opposes the force produced by the spring 10 and so the control system effectively operates in an identical manner. In other words, if control pressure Pc is reduced then the outlet pressure Po is increased. One advantage over the Fiσure 3 arrangement as opposed to the Figure 2 arrangement is that the additional chamber -.1 can effectively be retrofitted :o a single chamber pilot valve. However one disadvantage w th the dual chamber pilot valves of Figures 2 and 3 is that m both cases _ seal needs to be provided in order that the control fluid is prevented from entering the second part of the additional chamber i.e. that part of the chamber to which the control pressure is not applied. The provision of such a seal can be difficult and deterioration or failure of the _ __ ' } ma lead to reduction an performance of the pilot valve or leakage therefrom. Furthermore, the IJ ic Hυn caused by the seal can in turn create a frictio al error in the quality of the pilot valve control . Figure 4 shows a further "hydraulic" dual chamber pilot valve arrangement. As with the previous embodiments, a second chamber 40 is provided which is divided by a diaphragm 41 into .two parts- 42 and 43. The control pressure Pc iε applied to part 42 of the second chamber 40 and part 43 is cuiu-e Leu to the spring chamber which is vented to the atmosphere, As before, the diaphragm 41 is mechanically connected to the gate 8, in this case via the spring 10. However, unlike the embodiments of Figure 2 and Figure 3 in the embodiment of Figure 4 the control pressure Pc acts in the same direction as the forr.fi of . _ _ spring 10, rather than against it. This means that the control system or.κs in the opposite way to that of Figures 2 and 3 i.e. if the control pressure Pc is reduced then the gate 8 closes further, the venturi pressure Pv increases causing the PRV to close further and the outlet pressure to drop. This arrangement is not considered tc be "failsafe" since a loss of control pressure Pc would result in the lowest possible outlet pressure Po. This is sometimes referred to as a "direct acting" ' control system rather than the "reverse acting" control systems of Figures 2 and 3. The present invention aims to provide a pilot valve of the "reverse acting" type but which eliminates the need for a seal. In a first aspect, the present invention provides a pilot valve which includes bias3ing means to control a gate for controlling fluid flow through a control chamber; a second chamber sealed by a second chamber diaphragm into which control pressure is appliable for also controlling the operation of the gate, whereby in use an increase in control pressure acts to reduce fluid flow through the gate; wherein the side of the diaphragm against which the control pressure is not applied i .? in fluid communication with the control chamber. In th s way, a "reverse acting" dual chamber pilot valve is provided m which the need for any seal in association with the second chamber is avoided. The fluid which in use flows through the control chamber may nr may not be the same fluid or type of fluid aε the fluid which in uae is U3«d to apply the control pressure. The JJuids in question may, for example, be water or gas. In other words, in one example both fluids in question may be water; in another example both fluids may be gas; in a third example one fluid may be water and the other gas . Preferably, the biassing means is a spring means or spring such as a helical spring. Preferably the biassing means is biaεεed to open the gate and may be rigidly connected to e ydLe by a suitable mechanical linkage, preferably the diaphragm is also rigidly connected to the gate and/or biassing means via the same or a second suitable mechanical linkage. Preferably, the control chamber is at least partly bounded by a control cnamber diaphragm in addition to the second chamber diaphragm, Preferably biassing means is located on the opposite side of the control chamber diaphragm to the control chamber. As will e eΛplαi-.t-d in detail later ir. the spec r catioπ, by appropriately selecting the areas of the second chamber αiapr-rag and the control chamber diaphragm, the effect cf the control pressure or. the fluid flow through the control chamber (and therefore in use, on the outlet pressure) can be selected. In a preferred embodiment, the ratio of the area of the control chamber diaphragm to the second chamber diaphragm is 2;1 or less. For example, if the control chamber diaphrag is twice the area ot the second chamber diaphragm then a particular drop in control pressure will result in an identical increase in outlet pressure. In a different example, if the area of the second chamber diaphragm is three-quarters that of the control chamber diaphragm then an increase in control pressure of a given amount would cause the outlet pressure to decrease by three times that amount. The particular case in which the second chamber diaphragm area is half that of the control chamber diaphragm effectively replicates the function of the sandwich" and pancake" arrangements described earlier with reference to Figures 2 and 3. Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure . 13 a schematic diagram of a. single chamber pilot valve control arrangement; Figure 2 is a schematic diagram of a "sandwich" dual chamber pilot valve arrangement; Figure 3 is a schematic diagram of a "pancake- ' ' dual chamber pilot valve arrangement; Figure 4 is a schematic diagram of a "hydraulic" dual chamber pilot valve arrangement; and Figure 5 is a schema t ic diagram of a pilot v? 1 ve according to an embodiment of the present invention. Figure 5 shows a pilot valve 50 which includes a contrcl chamber 51 and a second chamber 52. A control pressure Pc is applied to chamber 52 in use and chamber 52 is divided from control chamber 51 by a second chamber diaphragm. 53. The second chamber diaphragm 53 is rigidly connected via linkage S4 to . gate mechanism 55. The gate mechanism 55 is also connected via a further rigid linkage 56 Lυ _ spring 57. The spring 57 is isolated from the control chamber 51 by the control chamber diaphragm 53. The action of the force of the spring 57 on the diaphragm 5Θ may be adjusted by adjustment screw 59. As can be seen from Figure 5, the control fluid (which may be ? m~ w . . er) presen in the control chamber 51 acts against the oppo ite side cf the second chamber ιυ diaphragm 53 to the control pressure Pc. I operation, if, for example, control pressure Pc is reduced then the gate 55 will open further causing the fluid flow through the control chamber to increase. When used in a PRV control circuit, as explained previously, this will cause the outlet pressure to increase. As indicated m Figure 5, he area of the control chamber diaphragm 53 is designated A and the area of Lhe second chamber diaphragm 53 is designated as A' . The balance of forces operating in the pilot valve is as follows: SF = APo - A'Po + A'?c - (A-A')Po + A'Pc In a first example, if A' = R SF = A r (Po + ?c) If a "multiplication" effect is required then the relative cross-section areas can be set to a different value. In a second example, if A' = 3/4 A, the equation will be SF = H A (Po + 3PC) T eitj υie n increase cf Fc of a given amount would cause Po tc decrease oy three times the amount and vice versa. The above embodiment is given by way of example only and variations will be apparent to those skilled in the art.

Claims: Cl aims 1. A pilot valve including biassing means to control a gate for controlling fluid flow through a control chamber; a second chamber sealed by a second chamber diaphragm into which control pressure is a p iable, for a 1 controlling the operation of the gate, v-hereby, in u$c, an increase in control ριet>suie ac b Lυ ed ce fluid flow through the gate; wherein the side of the diaphragm against which the control pressure is net applied, is in fluid communication with the control chamber. 2. A pilot valve according to claim 1 wherein the biassing means is biassed to open the gate. 3. A pilot valve according to claim 2 wherein the biassing means is rigidly connected to the gate by a mechanical linkage. 4. A pilot valve , according to claim 3 wherein the diaphragm is rigidly connected to the gate by a mechanical linkage . 5. A pilot valve according to claim 3 or claim 4 wherein the diaphragm is rigidly connected to the biassing means v a a mechanical linkage. 6. A pilot valve according to any one of tne preceding claims wherein the biassing means is a spring means. 7. A pilot valve accordinσ to claim 6 wherein the spring means is * hel cal s ri.πg. 8. A pilot valve according to any one of the preceding claims further including a control chamber diaphragm. 9. A pilot valve according to claim 8 wherein said biassing means is located on the opposite side of the control chamber diaphragm to the control chamber. 10. A pilot- al e according to any one of claims 8 or 9 wherein the ratio of the area of the control chamber c dy t i Lυ Lhe second chamber diaphragm is 2:1 or less.

Inventors: YONNET CLAUDE, YONNET, CLAUDE
Applicants: TECHNOLOG LTD, YONNET CLAUDE, TECHNOLOG LIMITED, YONNET, CLAUDE
Application year: 2000
Main classification: G05D16
IPC codes: G05D16