GB2170580A - Plug valve - Google Patents

Abstract

A fast acting plug valve comprises a hollow plug 10 slidable on a carrier 13 and sealing a neck at 29 between a pressure vessel, volume 1, and an outlet manifold 12. The plug 10 is urged into sealing engagement with the neck by increasing the gas pressure within the plug, volume 2, until it is at least equal to the pressure in volume 1. To open the plug valve, a pilot valve 18, 19, controlled by a magnetic spool valve 25 and pressure lines, is opened to allow gas in volume 2 to escape through an aperture 17 to a volume 3 at a lower pressure, so that pressure in volume 2 becomes less than pressure in volume 1. The pilot valve comprises a movable sealing ring 18 bearing on a sealing disc 19 carried by a shaft 20 connected to the plug, 10. The shaft 20 carries a damping stop 22 that during the opening of plug 10 enters the aperture 17 (Fig. 4) to reduce gas flow from volume 2 to volume 3. <IMAGE>

Description

SPECIFICATION Fast acting pneumatically operated valve The present invention relates to singe acting pneumatically operated valves particularly where high flow rates through the valve are required and the motive effort for valve operation is provided by a pressure differential across the sealing face of the valve.

Known high flow rate valves have hitherto employed an operating means which is separate from the closure which constitutes the moveable part of the valve. The operating means for such valves are usually a pneumatic piston and cylinder, with the piston motion linked mechanically to the valve closure.

A requirement for a high flow rate valve is that the valve closure moves to an open position in the least possible time, ie the closure has a high acceleration when opening. Valves using operating means linked mechanically to the valve closure are disadvantaged in that the inertia of the mechanical linkage in addition to the inertia of the pneumatic piston and the valve closure have to be overcome to open the valve. To provide a shorter opening time, such valves may employ a higher powered pneumatic piston and cylinder, but to withstand the higher pressure differentials the piston must necessarily be of more robust construction and hence heavier, thus diminishing the effect of the increased power.

An object of the present invention therefore, is to provide a fast acting pneumatically operated valve in which the valve closure and the operating means are linked to provide the minimum inertia for the valve opening force to overcome.

According to the present invention there is provided a plug valve assembly having a hollow sealing plug assembly slideably mounted on a carrier and wherein an external part of the plug assembly is in slideable sealing contact with a sealing neck, the sealing neck being between a pressure vessel and- an outlet manifold, valve operating means associated with the sealing plug, means for increasing gas pressure within the sealing plug so as to urge the sealing plug into sealing relationship with the sealing neck, and valve means associated with the sealing plug for dumping high pressure gas contained in the plug through the carrier whereby the pressure differential on the sealing plug is reversed and the sealing plug is urged away from the pressure vessel to thereby open the valve.

A particular advantage of the present invention is the short opening time achieved by linking the valve operating means directly to the sealing plug itself, thus reducing the inertia the sealing plug must overcome. In the construction of the present valve the linking of the system effectively makes the valve system self servoing.

According to another aspect of the present invention the sealing plug is hollow and the sealing plug contains valve operating means including two pressurisable volumes, linked by a closeable dumping aperture, the operating means being arranged so that the sealing ring and sealing disc move apart as the valve is opened, with the effect that the gas being retained within the plug assembly is used to assist in opening the plug valve.

In order that the present invention may be more fully understood one embodiment will be described with reference to the accompanying drawings of which: Figure 1 illustrates a sectional view of the plug valve in the closed position, Figures 2 to 5 show the operating sequence of the valve, in particular, Figure 2 shows the valve just after the initial opening stages of the valve have commenced.

Figure 3 shows the valve at a slightly later stage after the movement of the sealing plug has begun, Figure 4 shows the arrangement existing at the time the seal plug is open and being decelerated, Figure 5 shows the valve completely open at the end of the opening sequence.

Referring now to Figure 1.

The valve is shown in the closed position with the sealing plug 10, sealing the aperture between the pressure vessel, volume 1, and the outlet manifold 12. The sealing plug 10 is supported on a carrier portion 13 of an inner drum member 14. The carrier 13 is rigidly supported by a main support flange 1 5 via a spacer element 16. The sealing plug 10 is slideable over the carrier portion of the inner drum contains valve operating means. Two separate volumes are created within the valve, one being labelled 2 and being between the valve face and valve operating means of the other, volume 3 being between valve operating means and the inner drum walls. Effective gas tight seals (not shown) are provided between the sliding sealing surfaces of the plug 10 and carrier portion 13, and between the sealing plug and housing walls, 15, 16, 16a.

The two volumes are connected by dumping aperture 17. The dumping aperture is normally sealed by an annular sealing ring 18 bearing on disc 19 and connected to shaft 20. Shaft 20 is connected to the sealing plug face. The seal between annular sealing ring 18 and disc 19 may be supplemented by a rubber or plastics material sealing washer 21.

Also mounted on shaft 20 is an aperture stop 22 which controls the deceleration of the sealing plug 10. The limit of closing travel of the sealing plug 10 is controlled by linking stop 23 on the supporting structure and limiting stop 24 on the sealing plug 10. Annular sealing ring 18 is moveable, the movement being used to initiate the valve opening sequence. Valve operating means are contained in the housing 26.

Magnetic spool valve 25 controls pneumatic lines passing into housing 26, and thus the position of the annular sealing ring 18. Operation of the spool valve causes the annular sealing ring 18 to move away from the sealing disc 19 and break the seal. Housing 26 also provides support means for aperture stops 27 and spacer 28. A seal is present in the sealing neck between the neck and sealing plug 10. This captive 'o' ring type seal 29 assists in maintaining gas pressure in pressure vessel volume 1. A closeable gas feed 30 is provided in a wall of volume 3 to enable volume 3 to be pressurized or evacuated as desired, thereby providing means for adjusting opening characteristics of the valve.

The method of operation of the plug valve will now be described with reference to the figures. These figures have been simplified for clarity, and only the relevant operating features have been annotated.

Figure 1 shows the valve in a closed position. Prior to operation the volume 2 will be pressurised by pressurising means (not shown) to a pressure equal to or greater than the pressure to be generated in the pressure vessel, designated volume 1. The pressure is maintained in volume 2 by the seals notably between the annular sealing ring 18 and the sealing disc 19. Because the pressure in the volume 2 is at least equal to that in volume 1 the plug is maintained in its closed position by the pressure differential. When the valve is to be opened, a spool valve 25 is used to activate pneumatic operating means contained housing 26 to move the annular sealing ring 18 from its closed position and into volume 2 and thus breaking the sealing relationship with sealing disc 19. This allows the escape of gas from volume 2 to volume 3 which is maintained at a lower pressure than volume 2.Gas escapes through the dumping aperture which results between the sealing ring and annular disc. As the pressure in volume 2 falls below the pressure in volume 1 the pressure differential causes the sealing plug to be moved towards an open position.

The decreasing pressure in volume 2 resulting from the escape of gas causes the plug to be accelerated rapidly under the pressure differential. Figure 3 illustrates the plug moving to the open position, the sealing disc 19 connected to shaft 20 and the plug face will move into volume 3 so increasing the size of the dumping aperature so increasing the rate of dumping of higher pressure gas, increasing the pressure differential and thereby further accelerating the sealing plug. As can be seen from the arrangement in Figure 3 the design and position of the sealing plug is arranged to ensure the plug will be moving very rapidly at the time the seal between the plug and the pressure vessel is broken so permitting the passage of gas from volume 1 into the outlet manifold 12.During this intiial motion the piston velocity increases to a value which significantly reduces the complete opening time compared with a system in which the main seal opens immediately the plug starts to move.

Once the seal is broken and the annular outflow has begun the pressures in volumes 2 and 3 will tend to equilibrate and the piston acceleration will tend to become substantially constant. Further movement of the sealing plug after that time will result in the aperature stop 22 entering the dumping aperture with the effect that the flow of gas between volumes 2 and 3 will be significantly reduced, resulting in a pressure rise in volume 2 due to the contracting volume and a restricted escape route for the gas. This pressure build up will cause a deceleration of the seal plug 10.

This deceleration will significantly reduce the impact velocity of the seal plug on the aperture stops 27 and so reduce the bounce of the plug which would tend to push the plug back into the outlet manifold partially closing off the opening with the effect of making the valve opening time appear to be longer than it actually is. As the deceleration continues at a point shortly before the sealing plug impacts on the stop 27 the aperture stop 22 will pass completely through the dumping aperture so permitting the dumping of any residual high pressure gas in volume 2 to prevent rebound due to a gas pressure build up.

A particular advantage of the present system is the ability to tune the valve for particular requirements. The main shaft 20 may be provided with a screw thread to permit adjustment of the positions of the sealing disc 1 9 and aperture stop 22.

A further advantage of the present embodiment is that the aperture stop 22 may be adjusted in length and so enable the amount of damping to be varied by controlling the rate of and extent of pressure build up in volume 2 during valve opening.

It would also be possible by use of closeable aperture 30 for volume 3 to be maintained at reduced pressure or even evacuated if it were desired to minimise volume 3, or achieve a faster opening time.

According to one embodiment of the present invention the valve has a sealing plug of approximately 0.35 m diameter and a travel of approximately 0.25 m. The length of the plug is arranged so that after approximately 5 cm of travel the seal between the plug and throat is broken, so that the actual opening time is approximately half the transit time of approximately 0.14 seconds. It has been found that during the opening sequence the plug accelerates to a maximum velocity of 4.5 ms 5 and impacts with a velocity of approximately 0.5 ms l The valve may satisfactorily be operated with pressure differentials of up to 12 atmospheres. It should be noted that the above figures are given only by way of example and valves according to this design are not limited to the sizes and pressures given in the above example.

A further method of varying the operating characteristics of the plug valve is to employ a gas which is a mixture of Helium and Air, the mixture will bring about a variation in the speed of sound and thence operating characteristics.

Claims (8)

1. A plug valve assembly having a hollow sealing plug assembly slideably mounted on a carrier and wherein the plug assembly is moveable into slideable sealing contact within a sealing neck, the sealing neck being between a pressure vessel and an outlet manifold, means for increasing the gas pressure within the sealing plug so as to urge the sealing plug into sealing relationship with the sealing neck, and valve means associated with the sealing plug for dumping high pressure gas contained in the plug through the carrier, whereby the pressure differential on the sealing plug is reversed and the sealing plug is urged away from the pressure vessel to thereby open the valve.

2. A plug valv.e assembly according to claim 1 in which the sealing plug slides axially in the neck of the valve.

3. A plug valve assembly according to claims 1 or 2 including the valve operating means contained in the hollow sealing plug comprises a pressurisable volume, valve means for enabling the volume to be pressurised, a closeable dumping aperture for dumping high pressure gas, the dumping aperture being sealable in the contact region of a slideable sealing ring and a slideable sealing disc, the sealing ring and sealing disc being moved apart to dump high pressure gas contained in the pressurisable volume and thereby open the valve.

4. A plug valve operating assembly according to any of claims 1-3 wherein the slideable sealing ring and slideable sealing disc are mounted coaxially.

5. A plug valve assembly wherein the slideable sealing ring and slideable sealing disc are urged into sealing relationship when the pressurisable volume is pressurised.

6. A plug valve according to any of the preceding claims having connected to the interior of the hollow sealing plug a shaft, a sealing disc mounted on the shaft, a sealing ring located in a first pressurisable volume the sealing ring and disc being urged into sealing relationship when the pressurisable volume is pressurised, the sealing ring being moveable by valve operating means into the first pressurisable volume, the sealing disc and sealing ring moving in opposite directions in the dumping aperture to provide a self servoing valve opening system.

7. A plug valve assembly according to any of the preceding claims in which the valve operating means contained in a hollow sealing plug comprises a pressurisable volume, a second valve means for pressurising the volume, a dumping aperture for dumping high pressure gas from the pressurised volume to an unpressurised volume, the dumping aperture being sealable by a slideable sealing ring and a slideable sealing disc, the sealing ring and disc being moveable by pneumatically operated valve means.

8. A plug valve assembly substantially as hereinbefore described with reference to the accompanying drawings.