GB1571684A - Fluidoperable valve - Google Patents

Description

(54) FLUID-OPERABLE VALVE (71) We, MARTONAIR LIMITED, a British Company, of St. Margarets Road, Twickenham, Middlesex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a fluid-operable valve and is particularly concerned with a valve having a valve member movable from a first flow-controlling position to a second flow-controlling position by the application to the valve member of at least one positioning pressure signal.Where the valve member is biased to return to said first flowcontrolling position on interruption to the supply, or reduction below a predetermined pressure, of a pressurised fluid whose flow through the valve is controlled by the valve member, the valve is normally called a "failsafe" type of valve since the valve member will automatically return to said first position on interruption or reduction in pressure of the pressurised fluid supply.

In a known valve of this kind in which the valve member is a piston, a positioning pressure signal derived from the pressurised fluid supply is applied to one end of the piston and a spring of suitable rate acts on the piston in opposition to the positioning signal. Thus on interruption, or fall in pressure to a predetermined value, of the pressurised fluid supply, the positioning signal will also cease or fall in pressure and the spring will move the piston to its "fail-safe" position.Where the valve is to be employed for- use with a pressurised fluid supply which could have a normal pressure within a considerable range of pressures, say between 2 and 10 bars, the spring would have to be sufficiently powerful to return the valve to the fail-safe from the maximum pressure condition and therefore the positioning pressure signal would have to be correspondingly high or the area of the piston to which the positioning pressure signal is applied would have to be excessively large.

According to the invention, a fluidoperable valve includes a valve member which is movable from a first flow-controlling position to a second flowcontrolling position by the application to the valve member of at least one positioning pressure signal, the valve also including a pressure-responsive member which is biased by resilient means acting thereon to a position in which the pressure-responsive member holds the valve member in said first flow-controlling position either by direct engagement therewith or indirectly through the resilient means, except durng normal operation of the valve, when the pressure-responsive member is acted upon by a holding pressure opposing the force of said resilient means and provided the or each positioning pressure signal has first been removed or is insufficient to oppose the force of said re silient means.

The holding pressure may be provided by or derived from a pressurised fluid supply whose flow is being controlled by the valve.

Alternatively the holding pressure may be independent of the pressurised fluid supply whose flow is being controlled by the valve.

Usually the valve member is moved from said first to said second operative positions by a positioning pressure signal which is a function of the pressurised fluid supply controlled by the valve and so the positioning pressure signal will cease or fall when the fluid supply pressure is interrupted or falls.

However, in some applications of the valve, the positioning pressure signal may be independent of the fluid supply pressure or the valve member may be subjected to more than one independent positioning pressure signals; for example, as would be the case in a memory type of valve.

Conveniently, the valve member is a main piston and the pressure-responsive member is an auxiliary piston mounted in the same housing as the main piston and biased by a spring towards the main piston to move the latter from said second to said first operative position, the auxiliary piston being held, when the main piston is in said second position, by the holding pressure away from the main piston against the force of the spring, whereby on interruption or reduction of the holding pressure below a predetermined value, the auxiliary piston will be moved by the spring to move the piston into and to hold the main piston in said first operative position.

Alternatively, the valve member may be a main piston slidable in a cylinder between said first and said second flow-controlling positions, the pressure-responsive member being an auxiliary piston also slidable in the cylinder and the resilient means being a compression spring acting between the two pistons to urge them apart, the valve also including means for applying a holding pressure to the auxiliary piston in opposition to the spring force, whereby- during normal operation, the holding pressure is sufficient to oppose the spring force and to move the auxiliary piston into engagement with the main piston, the two pistons then being movable between said first and second flow-controlling positions as if they were a single piston, and, when the holding pressure falls below a predetermined value and the or each positioning sigial has been removed, the spring force will urge the two pistons apart into respective engagement with spaced end faces of the cylinder, the main piston in that position being in said first flow-controlling position.

By way of example several embodiments of valve in accordance with the invention are now described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic axial section through a first valve; Figure 2 is a diagrammatic axial section through a second valve; Figure 3 is an axial section of a practicable version of the valve shown in Figure 1; Figure 4 is an axial section of a practicable version of a valve similar to that shown in Figure 3, except that a positioning pressure signal is applied to an auxiliary piston arranged similarly to that in Figure 2; Figure 5 is an axial section through a third valve shown in a "fail-safe" position;; Figure 6 is a similar view of the valve shown in Figure 5 showing its main piston in said first flow-controlling position, but operative to enable the main piston to be moved into said second flow-controlling position, and Figures 7 and 8 are axial sections through a fourth valve and corresponding respectively to Figures 5 and 6.

Referring to Figure 1, the valve comprises a housing 1 containing a main piston 2 being the aforesaid valve member. The housing 1 has an inlet port 3 for a pres surtqed fluid supply P. The port 3 com muaicates with an output port 0 through an annular groove 4 formed around the piston 2 when the piston 2 is in a "fail-safe" position, as illustrated. This is the aforesaid first operative position. The piston 2 is movable downwardly in the Figure to the aforesaid second operative position in which the port 3 communicates through the groove 4 with a second output port 01. The housing is provided with exhaust ports and the piston has two more grooves similar to the groove 4 but these are not referred to in this description and so are not given reference numbers. The piston 2 carries sealing '0' rings 5.The piston 2 has an enlarged end portion 6 carrying an '0' ring 7 and arranged to run in a chamber 8 defined in the upper end of the housing 1 and closed by an end plate 9. The end portion 6 is acted upon by a positioning signal St, applied through a port 10 in the end plate 9. The positioning signal Si, may be a derivative of the pressure of the fluid supply or an independent signal and while it is applied, the piston 2 is held in the second operative position in which the supplied fluid P flows through the port 3, the groove 4 to the outlet port '0'. The housing 1 defines a lower chamber 11 in which moves an auxiliary piston 12 carrying an '0' ring 13, the chamber 11 being closed by an end plate 14.The auxiliary piston 12 constitutes the aforesaid pressure-responsive member and is biased upwardly, as viewed in the Figure (by a helical compression spring 15 acting between the auxiliary piston 12 and the end plate 14. The auxiliary piston 12 has a coaxial extension 16 which when the piston 12 is biased by the spring 15 to the upper end of the chamber 11 will engage the piston 2 and move the latter to the "fail-safe" position, as illustrated. The auxiliary piston 12 is, however, held downwardly against the spring 15 to the position ilustrated, when the pressurised fluid supply P is admitted through the port 3, as the groove 4 communicates through an internal duct 17 in the piston 2 to the chamber 11. When the supply P fails or its pressure falls below a predetermined value, the downward fluid force on the auxiliary piston 12 can no longer oppose the upward force of the spring 15 and the auxiliary piston 12 moves upwardly to push the piston 2 to the "failsafe" position, as illustrated. Where the positioning signal Si is a derivative of P, there will be no opposition by Si, to the upward movement of the piston 2 and where the positioning signal S1, is independent of P, this will be insufficient to oppose the up ward movement of the piston 2 produced by upward movement of the auxiliary piston 12.

In Figure 2, like parts are shown by the reference numerals used in Figure 1. The principal difference is that the auxiliary piston 12 is housed in a separate housing 20 which is supplied with a pressurised fluid signal Pa through a port 21 leading to a chamber 22 in the housing 20 above the piston 12, as viewed in the Figure. The pressure of Pa is derived from the fluid supply P and so failure or fall of P will produce failure or fall of Pa and thus the spring 15 will move the piston 12 upward, as viewed in the drawing, to cause the extension 16 to engage the piston 2 and hence retum the latter to the "fail-safe" position as illustrated. Another difference in this valve is that a second positioning signal S, is applied to the piston 2 to provide a memory function.

Although the valves of Figures 1 and 2 are shown with their pistons upright they may be used in any position.

Figure 3 shows a practicable form of the valve shown in Figure 1 and like parts are shown by the same reference numerals. The piston 2 is slidable in a ported sealing tube 23 positioned in the housing 1.

Figure 4 shows a practicable form of valve similar to that shown in Figure 2 with regard to the application of the pressurised fluid positioning signal Pa, otherwise the valve is similar to that of Figure 3 and the same reference numerals have been usd for parts also appearing in Figure 3. The positioning signal Pa may b the same as P and an inlet port 25 for the positioning signal Pa may be connected to the port 3 by tubing externally of the housing 1.

Referring now to Figures 5 and 6, the third valve comprises a housing 31 having a cylindrical bore in which a main piston 32 (constituting the aforesaid valve member) is slidable from a first flow-controlling position, as illustrated, in which an inlet port to which a fluid at pressure P is applied is connected with the upper port 0 of a pair of outlet ports 0, O1 to a second flow-controlling position in which the inlet port P is connected instead with the lower outlet port 01. The movement of the main piston 32 from the first to the second flow-controlling position is effected by a positioning signal Sl applied through a port 40 in an upper end-plate 33 of the housing against a larger diameter end portion 34 of the main piston 32.The valve also includes an auxiliary piston 35 (constituting the aforesaid pressure-responsive member) slidable in the cylindrical bore and having an axial extension 36 which is inserted in sockets 37 formed in the adjacent end of the main piston 32. The main piston 32 and the auxiliary piston 35 are urged apart to the position shown in Figure 5 by a helical compression spring 38 positioned in a central passageway in the main piston 32. In the position shown in Figure 5, the spring 38 has pushed the main piston 32 against the upper end-plate 33 and the auxiliary piston 35 against a lower end-plate 39. The latter has a port 41 therein to which the aforesaid reference pressure Pa is applied.The main piston 32 is fitted with '0' rings 42 which isolate the fluid P from end portions 43, 44 of the bore in the housing 31 in which the upper end portion 34 of the main piston 32 and the auxiliary piston are respectively slidable. The upper end portion 34 of the main piston 32 carries an '0' ring 45 dividing the bore portion 43 into two parts. Similarly the auxiliary piston 35 carries an 'O' ring 46 which divides the bore portion 44 into two parts. An exhaust port 47 is provided from the bore portion 43 below the '0' rings 45 to permit air to be displaced from the bore portion 44 through the central passageway in the main piston 32 and from the bore portion 43 on movement of the main and auxiliary pistons.

The main and auxiliary pistons are always in the respective positions shown in Figure 5 when the holding pressure Pa is zero, i.e.

when no holding pressure acts on the auxiliary piston 35 through the port 41, as in this condition, the spring 38 extends to hold the main piston 32 against the end-plate 33 and the auxiliary piston 35 against the endplate 39. The spring force alone is sufficient to move the main piston 32 when the positioning signal S1 is removed. When the correct holding pressure Pa is applied through the port 41, the auxiliary piston 35 is urged upward, as shown in Figure 6, to compress the spring 38 until the axial extension 36 of the auxiliary piston 35 has engaged the inner end of the socket 37.In this condition, the application of the positioning signal S1 will move the main piston 32 downward into the second flow-controlling position together with the auxiliary piston, both pistons moving as though they were a single piston and the spring 38 having no effect. Assuming that the positioning signal 5 has been removed, as soon as the holding pressure Pa falls below a predetermined value or fails, the spring 38 will expand and return both pistons to a "fail-safe" position shown in Figure 5.

The holding pressure Pa may be independent of the pressure of the controlled fluid P or it may be derived therefrom.

The valve shown in Figures 7 and 8 is substantially the same as that shown in Figures 5 and 6, except that the auxiliary piston 50 slides within the socket 37 in the main piston 32 instead of in the cylindrical bore in the housing 31. An '0' ring 51 seals an end portion 52 of the cylindrical bore to which the holding pressure Pa is applied through the port 41 from the central pas sageway in the main piston 32. All other parts of the valve are given the same reference numbers as in Figures 5 and 6 and the valve behaves in a similar manner.

Claims (9)

WHAT WE CLAIM IS:-

1. A fluid-operable valve including a valve member which is movable from a first flow-controlling position to a second flowcontrolling position by the application to the valve member of at least one positioning pressure signal, the valve also including a pressure-responsive member which is biased by resilient means acting thereon to a position in which the pressure-responsive member holds the valve member in said first flow-controlling position either by direct engagement therewith or indirectly through the resilient means, except durng normal operation of the valve, when the pressure-responsive member is acted upon by a holding pressure opposing the force of said resilient means and provided the or each positioning pressure signal has first been removed or is insufficient to oppose the force of said resilient means.

2. A valve as claimed in Claim 1 in which the holding pressure is provided by or is derived from a pressurised supply whose flow is being controlled by the valve.

3. A valve as claimed in Claim 1 in which the holding pressure is independent of a pressurised fluid supply whose flow is being controlled by the valve.

4. A valve as claimed in any preceding claim in which the valve member is a main piston and the pressure-responsive member is an auxiliary piston mounted in the same housing as the main piston and biased by a spring towards the main piston to move the latter from said second to said first operative position, the auxiliary piston being held, when the main piston is in said second position, by the holding pressure away from the main piston against the force of the spring, whereby on interruption or reduction of the holding pressure below a predetermined value, the auxiliary piston will be moved by the spring to move the main piston into and to hold the main piston in said first operative position.

5. A valve as claimed in any of Claims 1-3 in which the valve member is a main piston slidable in a cylinder between said first and second flow-controlling positions, the pressure-responsive member being an auxiliary piston also slidable in the cylinder and the resilient means being a compressioq spring acting between the two pistons to urge them apart, the valve also including means for applying a holding pressure to the auxiliary piston in opposition to the spring force, whereby during normal operation, the holding pressure is sufficient to oppose the spring force and to move the auxiliary piston into engagement with the main piston, the two pistons then being movable between said first and second flow-controlling positions as if they were a single piston, and, when the holding pressure falls below a predetermined value and the or each positioning signal has been removed, the spring force will urge the two pistons apart into respective engagement with spaced end faces of the cylinder, the main piston in that position being in said first flow-controlling position.

6. A fluid-operable valve constructed and arranged substantially as described herein with reference to and as shown in Figures 1 and 3 of the accompanying drawings.

7. A fluid-operable valve constructed and arranged substantially as described herein with reference to and as shown in Figures 2 and 4 of the accompanying drawings.

8. A fluid-operable valve constructed and arranged substantially as described herein with reference to and as shown in Figures 5 and 6 of the accompanying drawings.

9. A fluid-operable valve constructed and arranged substantially as described herein with reference to and as shown in Figures 7 and 8 of the accompanying drawings.