GB2186664A

GB2186664A - Valve

Info

Publication number: GB2186664A
Application number: GB08700369A
Authority: GB
Inventors: Alan David Hall
Original assignee: Goodwin R International Ltd
Current assignee: Goodwin R International Ltd
Priority date: 1986-01-10
Filing date: 1987-01-08
Publication date: 1987-08-19
Also published as: GB8600538D0; GB8700369D0; GB2186664B

Abstract

In an axial fluid flow control valve having a valve casing 10 with an inlet and an outlet at opposite axial ends, an inner housing 18 mounted within the casing, a flow path between the inlet and outlet passing around the exterior of the housing, a valve element 15 movably supported within the housing and closing the housing and movable to and from a position in which it engages a valve seat 14 around one of the inlet or outlet to close the flow path, the casing and housing being unitary, the valve element 15 has at least one balancing passage 24 therethrough so that the pressure on the interior of the housing may be balanced with the pressure at the side of the valve element remote from the interior of the housing, and an actuator for the valve element comprises a transverse rotatable shaft 19 passing through the casing and housing and a crank 27 mounted on the shaft and connected to the valve element. A pilot valve (30 Fig. 3) may be mounted with lost motion within the valve element 15 or transverse secondary flow paths (40 Fig. 4) may be provided through the valve element 15 to provide a throttled valve, these paths being closed when the element 15 is fully withdrawn into the housing. <IMAGE>

Description

SPECIFICATION Reciprocating piston type valve This invention relates to an axial reciprocating piston type valve for controlling fluid flow.

There are two main types of fluid flow control valve, namely shut-off valves which are only intended to be open or closed, but which are not required to perform any accurate control over the rate of fluid flow, and flow control valves which can be operated to provide accurate control over the rate of flow.

Examples of existing designs of such valves include gate valves, slide valves, ball valves and butterfly valves, and all of these valves suffer from the disadvantage that a valve closure element therein is exposed to a much greater pressure on its upstream face than on its downstream face, so that a substantial actuating force has to be exerted in order to effect opening and closing of the valve. Furthermore, the closure elements present a substantial obstacle to fluid flow through the valve, when in partly-open positions, such as to impede generally streamline flow through the valve and to create turbulence with resultant pressure loss and reduction in the potential rate of flow through the valve.This results in the necessity to provide higher output pumps in a pipe system provided with the valve, and also means that valve sizes must be larger than would be necessary if more streamlined flow conditions through the valve could be obtained.

In addition, very substantial erosive forces are generated, caused by the increased throttling speed of the fluid, and these occur across the same section of the closure elements and the related valve seat when the elements approach the fully closed position leading to wear.

According to the invention there is provided an axial fluid flow control valve having a valve casing with an inlet and an outlet at opposite axial ends, an inner housing mounted within the casing, a flow path between the inlet and outlet passing around the exterior of the housing, a valve element movably supported within the housing and closing the housing and movable to and from a position in which it engages a valve seat around one of the inlet or outlet to close the flow path, the casing and housing being unitary, the valve element having at least one balancing passage therethrough so that the pressure on the interior of the housing is balanced with the pressure at the side of the valve element remote from the interior of the housing, and an actuator for the valve element comprising a transverse rotatable shaft passing through the casing and housing and a crank mounted on the shaft and connected to the valve element.

The valve of the invention has many advantages. The fact that the casing and housing and unitary leads to great strength and leaktightness so that the valve can be specified for extreme situations. That it is an axial valve means that pressure drop when fully open is minimised. Having the valve element balanced means it is easy to operate and in particular to operate accurately to control flow rate. Further, it is in many embodiments bidirectional, and the construction is such that there need be only one dynamic seal.

Preferably, there is a seal between the housing and the valve element which includes piston rings mounted on the valve element.

There may also be a metal to metal seal where the valve element contacts the valve seat. Due to this, the valve is largely fire proof, in that while it may also have soft seals, particularly between valve element and housing, these have the back up of metalmetal seals which will survive high temperature exposure. There may be a replacable valve seat element surrounding the said one of the inlet or outlet.

Preferably, full travel of the valve element is accomplished with not more than 1200 rotation of the rotatable shaft. Most preferably 90" rotation causes full travel. This feature allows very rapid operation.

In some embodiments the valve element has a pilot valve slidable within it to and from a position in which it closes the at least one balancing passage, and the valve element includes side ports to communicate the interior of the housing with the other of the inlet or outlet so that, when the pilot valve opens the balancing passage, the interior of the piston is accessible from the inlet and the outlet.

Further embodiments may include one or more secondary flow paths between the inlet and outlet through the valve element, said flow path(s) being opened upon opening movement of the valve element before it comes away from the valve seat.

With this feature, the valve can operate as a shut-off valve, by virtue of the engagement and disengagement of the valve element with the valve seat, and can also operate as a flow control valve by controlled opening movement of the piston relative to the valve seat so as to bring the transverse flow passage into controlled communication with the passage through the valve between inlet and outlet.

A nose portion of the valve element can include a plurality of transverse through-passages which are axially spaced from each other, so that progressive withdrawal of the valve element from the valve seat will be accompanied by increase in the number of passages which are effective. The through-passages conveniently may comprise radial ports which extend inwardly from the outer circumference of the nose portion of the valve element to a common central port formed in the nose portion and also, preferably, communicating with the interior of the housing. In one mode of operation of the valve, the part where the valve seat is provided forms the outlet of the valve. However, the valve may be reversible in operation, and still function satisfactorily as a shut-off valve and a flow control valve, by arranging for the housing port section to form the inlet of the valve.

The provision of the transverse rotatable actuator shaft means that any axial thrust which may be applied to the piston by fluid supplied to and/or passing through the valve will apply a transverse force to the shaft, rather than an axial (blow-out) force along the length of the shaft, thereby minimising the risk of the actuator shaft being dislodged forcibly from its mounting in the housing in any pressure overload situation which might develop. To further safeguard the actuator shaft against dislodgement, an overload or blow-out preventer may be mounted in the housing to engage a captive portion of the actuator shaft.

In order that the invention may be more clearly understood, the following description is given by way of example only with reference to the accompanying drawings in which: Figures 1 and 2 are respectively a longitudinal and a transverse sectional view of a valve of the invention in closed position.

Figure 3 is of a modified valve of the invention having a piston valve and shown in longitudinal cross section and Figure 4 is a longitudinal cross section of another valve of the invention.

Referring now to Figures 1 and 2 of the drawings, there is shown a first embodiment of axial reciprocating piston type valve according to the invention which comprises a valve casing 10, a fluid inlet 11 and a fluid outlet 12 with a generally axial fluid flow path 13 between them. The inlet and outlet can, in most instances, be interchanged to be at the other end of the casing. There is an annular valve seat 14 arranged between the inlet 11 and the outlet 12, a valve element or piston 15 movable axially between open and closed positions with respect to the valve seat 14, and a valve actuator, designated generally by reference numeral 16, which is coupled with the valve piston 15 to control the movement of the latter.

The annular valve seat 14 is provided on a housing port section 1 7 which can function as the fluid inlet or the fluid outlet as required.

Within the casing 10 and unitary therewith is a internal housing 18 within which the piston 15 is slidably movably and into which the actuator 16 extends to move the piston. The actuator has a rotatable shaft 19 which passes through bosses inter-connecting the casing and housing and extends to the exterior of the housing where it may be attached to a gear box not shown operable by a hand wheel. The housing 18 is also attached to the interior of the casing 10 by means of a streamlined part 20 spaced to the right of the bosses as shown in Figure 1 and thus increasing the security of positioning of the housing 18 in the casing 10. The fluid flow path 13 is therefore divided by the member 20 and also the bosses for the rotatable shaft 19 as shown in Figure 2.Other arrangements for securing the housing integrally within the casing may be employed for instance the fluid flow path 13 may be divided into a further number of passages.

As shown in Figure 1, at the outlet 12 there is an annular port section 17 having a metal seal surface at its inner end where it will be contacted by the rim of the piston 15.

This section 17 is replacable. Inwards of the section is a further annular part 21 having a soft seal indicated at 22 engagable with the piston 15 when that is in the closed position.

There is also a soft seal between parts 21 and 1 7 and another one between the exterior of the section 1 7 and the interior of the casing 10. The presence of the metal to metal contact ensures that this part of the valve is fire proof.

The piston 15 is formed in three parts, including a main part 23 with a projected nose having a plurality of passages 24 extending therethrough. This part 23 is hollow and is threadedly attached to a rear part 25 between which is clamped a ring 26 with soft seals between it and the parts 23 and 25. On the exterior of the ring 26 are sprung seals slidingly engaging the interior of the housing 1 8. In each of the parts 23 and 25 are grooves each containing two piston rings so that there is also a metal to metal sliding seal between the piston 15 and the interior of the housing 18 so that again this arrangement is fire proof.

Parts 23, 26 and 25 are hollow so that ports 24 communicate the pressure at the right, at the outlet 12, with the interior of the housing 18.

Splined on the rotatable shaft 19 is a link 27 connected by a toggle 28 to the part 25 of the piston 15. Preferably a turn of 90" or at most 1200 of the shaft 1 9 is sufficient to cause maximum stroke of the piston 15 between the fully closed position in which it is shown in Figure 1 and the fully open position in which it is withdrawn into the housing 18, except for its projecting nose which is so shaped as to allow relatively turbulent free flow of fluid through the valve when open.

As shown in Figure 2 the splined shaft 19 extends into a sleeve bearing 29 for a short distance at one end, and into a second sleeve bearing 30 as it passes completely through the casing 10 to the exterior. The shaft is wider where it is within the housing 1 8 than the bore outwards through the casing, so that blow out of the shaft is virtually impossible.

Assembly has been via a wider bore in the other direction, which is closed by a cap 31.

A seal arrangement at 32 including at least three seals is provided where the shaft passes out of the casing 10.

In use of this valve, if the inlet 11 is at high pressure and the outlet 12 at low pressure the interior of the housing 18 is, due to the ports 24, balanced at the same low pressure as the outlet 12. Accordingly only little force is needed to move the piston 15 as far as possible or as required from the fully closed position. Once it is slightly open change in pressure on the down stream face of the piston 15 will be reflected in a change in pressure in the inside. Because of the same effective areas being available on both sides of the piston there will still be very light operation allowing exact positioning of the piston 15.

The valve is bidirectional so that if the end part 12 becomes the high pressure inlet the same balancing obtains, with the difference that in this case the high pressure is found within the housing 1 8 and thus that may find its way to the seal 32 which is designed fully to withstand this pressure. In both situations the arrangement of sliding dynamic seals on the parts 23, 25 and 16 of the piston 15 can withstand the pressure difference between the two sides of the valve. This is why the piston rings are provided as well as the soft seals which comprise spring energised polytetrafluoroethylene seals.

The fact that the splined shaft is transverse means that space is saved, the chances of shaft blow out are virtually eliminated and the number of dynamic seals is also reduced. The splined connection between the shaft 19 and the part 27 ensures that there is no backlash allowing accurate modulation. Supporting the shaft on both sides reduces its potential for deflection.

Figure 3 shows a modified valve according to the invention, in partial form, with like parts being given like reference numerals. Compared with the embodiment of Figures 1 and 2 the differences lie in the piston 1 5 which in this construction has a pilot piston in it at 30.

This is slidable within a boss 31 mounted on the interior of a main part 32 of the piston through which the passages 24 extend. The main part 32 also has transverse bores 33 by which the interior of the housing 1 8 is connected to the pressure at the left end 11 of the chamber. The pilot piston 30 is movable with limited lost motion within the piston 15, being stopped on the right when it engages a seat whereupon it closes the passage 24, and being stopped on the left by abutting a ring 34 bolted to the left end of the main part 32 of the piston. The main part 32 of the piston has sliding seals with the interior of the housing 18. The drive arrangement operates on the pilot piston in the same way as in the other embodiment it operates on the piston as such.

In operation of this embodiment the high pressure is at the left end so that 11 is the inlet and 12 is the outlet. This means that the interior of the housing is connected via the openings 33 to the high pressure and so the sliding seals between the piston 15 and the interior of the housing 18 are not subject to a pressure differential. Relatively small force is needed to move the pilot piston 30 somewhat to the left as shown whereupon high pressure can vent through the passages 24 and increase the pressure on the downstream side at 12. Once the pilot piston has moved to the left as shown by the amount of lost motion to contact the ring 34 pressure has built up on the side 12 and it is a relatively easy matter to move the main part 32 of the piston so as to open it and open the metal to metal seals between that and the ring 21.

This embodiment is unidirectional, and if high pressure were applied to the end marked 12 the piston would not be balanced. The apertures 23 become covered by the wall of the housing 18 when the piston withdraws to the left. Again the seating ring 21 is replacable. A projection on the pilot valve engages a bore in the end of part 32 for guidance.

This embodiment is suitable for high and low temperature operation because no soft seals are needed and so fire proofness is particulary good. However it lacks the facility of closely controlled closing because of the lost motion connection between the pilot valve 30 and the rest of the piston 15.

In the embodiment of Figure 4 like parts are again given like reference numerals. There is a slightly different connecting arrangement between the rotatable shaft which is of square cross section and the crank 27. The connector 28 is also shown on a different shape. In this case the passages between the side 12 and the interior of the housing 18 are represented as a single passage inclined to the axis from a recess 24 in the end of the piston.

Extending radially outwardly from the recess 24 are a plurality of passages 40 terminating against a seal face 41 on the interior of the part 17. The purpose of these is as follows.

The piston is balanced, whichever side is at higher pressure, and can be withdrawn from the closed position shown by an accurately controlled amount and if desired one or more or all three of the transverse passages 40 can be uncovered from contact with the sealed surface 41 whereupon a small flow path exists beteen up stream and down stream sides of the valve even though the valve has not come fully away from the valve seat. Thus this embodiment can take up partly open positions in which there is a throttling effect to control the rate of flow, or a fully open position in which the piston is entirely received in the housing 18.

In the valve, less turbulence is generated as compared with existing designs, by virtue of the generally axial fluid flow through the valve, and the manner by which the piston engages and disengages the valve seat. Further, the arrangement is such that the piston presents less resistance to steamline through-flow of fluid than the closure members of existing designs of valve.

Claims

1. An axial fluid flow control valve having a valve casing with an inlet and an outlet at opposite axial ends, an inner housing mounted within the casing, a flow path between the inlet and outlet passing around the exterior of the housing, a valve element movably supported within the housing and closing the housing and movable to and from a position in which it engages a valve seat around one of the inlet or outlet to close the flow path, the casing and housing being unitary the valve element having at least one balancing passage therethrough so that the pressure on the interior of the housing is balanced with the pressure at the side of the valve element remote from the interior of the housing, and an actuator for the valve element comprising a transverse rotatable shaft passing through the casing and housing and a crank mounted on the shaft and connected to the valve element.

2. A valve according to Claim 1 wherein there is a seal between the housing and the valve element which includes piston rings mounted on the valve element.

3. A valve according to Claim 1 or 2 wherein there is a metal to metal seal where the valve element contacts the valve seat.

4. A valve according to Claim 3 including a replacable valve seat element surrounding the said one of the inlet or outlet.

5. A valve according to claim 1, 2, 3 or 4 wherein full travel of the valve element is accomplished with not more than 120 rotation of the rotatable shaft.

6. A valve according to any preceding claim including a splined connection between the rotatable shaft and the crank.

7. A valve according to any preceding claim wherein the part of the shaft within the housing is wider than the bore through which the shaft passes to the exterior of the casing so as to prevent blow-out through said bore.

8. A valve according to any preceding claim wherein the valve element has a pilot valve slidable within it to and from a position in which it closes the at least one balancing passage, and the valve element includes side ports to communicate the interior of the housing with the other of the inlet or outlet so that, when the pilot valve opens the balancing passage, the interior of the piston is accessible from the inlet and the outlet.

9. A valve according to claim 8 wherein the pilot valve is connected to the crank and has a lost motion connection with the piston.

10. A valve according to any one of Claim 1 to 7 including one or more secondary flow paths between the inlet and outlet through the valve element, said flow path(s) being opened upon opening movement of the valve element before it comes away from the valve seat.

11. A valve according to Claim 10 wherein the secondary flow paths are closed when the valve element is moved fully away from the seat into the housing.

12. An axial fluid flow valve constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

13. A valve according to claim 12 modified substantially as hereinbefore described with reference to and as illustrated in Figure 3 of the accompanying drawings

14. A valve according to Claim 12 modified substantially as hereinbefore described with reference to and as illustrated in Figure 4 of the accompanying drawings.