GB2042687A

GB2042687A - Steam Turbine Control Valve

Info

Publication number: GB2042687A
Application number: GB8002283A
Authority: GB
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1979-02-16
Filing date: 1980-01-23
Publication date: 1980-09-24
Also published as: GB2042687B

Abstract

Before the valve closure member 14 leaves its seat, inlet ports 37 in the member are uncovered by movement of a further member 30 having a lost- motion connection with the closure member. Flow through the ports 37 passes out through further ports 38 to the valve outlet 12. Thus the pressure difference is reduced across the closure member so that when the closure member leaves the seat, flow adheres to the curved wall 13 of the seat whereby jet-flow interaction and noise are eliminated. <IMAGE>

Description

SPECIFICATION Fluid-flow Control Valve This invention relates to steam turbine control valves.

Fluid-flow control valves, especially those which produce a throttling or pressure-reducing effect, constitute a major noise source in the chemical industry and in other systems where the flow of high-pressure fluid is controlled at various stages by valves. This noise generates acoustical waves which produce vibrations in the valve body and associated pipework which is such that it may cause damage to equipment, associated support structures and may also be injurious to human hearing.

In steam turbine installations governing valve noise is dominant at partial-load valve opening conditions where the pressure ratio is high and mass flow-rate is low.

In the past many proposals have been made to reduce the effect of valve noise, for example, down-stream silencing of the associated pipework, and although such proposals may reduce the noise downstream they make no reduction in the noise emanating from the valve.

Proposals for reducing the noise emanating from the valve are disclosed in British Patents 278,451 and 1,248,370 as well as in United States Patents 3,776,278, 3,857,542 and 4,066,100. These disclose the use of "strainers" and "mufflers". "Strainers" usually take the form of one or more thin perforated plates or rings positioned in the valve seating region and have the effect of breaking down large-scale turbulence in the fluid-flow path at the expense of increasing small-scale turbulence. "Mufflers" usually consist of an arrangement of small-bore passages in the valve plug which break-down the flow of fluid into a series of small jets. These passages have sometimes beem employed to promote a more desirable flow condition but they do cause cross-jet turbulence down-stream of the valve seat which provide a further cause of noise.

Both "strainers" and "mufflers" have the effect of producing a greater pressure drop than may be acceptable at large valve openings.

The object of this invention is to provide a fluid-flow control valve whereby noise and subsequently vibration may be considerably reduced below that of prior art valves.

According to the present invention a steam turbine control valve comprises a hollow valve member movable within a hollow valve body which has an inlet port, and outlet port and a generally convex valve seat for co-operation with the valve member to block the flow of fluid past the valve member when the latter is seated, the valve member having a plurality of inlet ports upstream of the seat which are progressively openable by movement of a further member relative to the valve member while the latter is seated and the valve member also having a plurality of outlet ports which open into the outlet port.

Preferably the valve member has a cavity defined in part by a flat bottom wall through which the outlet ports pass.

The inlet ports in one embodiment may be located in a cylindrical wall of the valve member and said further member is slidable within the valve member.

Preferably, there is a lost-motion connection between the two members and a spring which acts on the further member and on the valve member in a sense corresponding to movement towards the seat.

Preferably, a pressure-balancing passage passes through the valve member to reduce the force required for valve operation.

A valve will now be described, by way of example to illustrate the invention with reference to the accompanying drawings in which: Figure 1 is a cross-sectional elevation of a steam turbine governing valve in its closed position.

Figure 2 is a cross-sectional elevation of the valve shown in Figure 1 in a partially-open position.

Figure 3 is a cross-sectional elevation of the valve shown in Figures 1 and 2 in its fully-open position.

The valve comprises a hollow body 10 having a steam-inlet port 11 and a steam-outlet port 1 2 and formed to provide a circular convex valve seat 1 3. The seat 1 3 co-operates with a convex region 1 8a of a rim 18 formed on a valve member 14.

The valve member 14 is a hollow cylindrical member with a flat bottom wall 15 joined to a side wall 19, which is slidable within a guide portion 29 of a closure 28. An annular flared concave wall section 1 7 merges with the convex region 18a. The rim 1 8 merges with the upper side wall 19. The wall 1 5 has a cylindrical lower external shape at 16. The valve member 14 has a pressure-balancing through passage 21 within a tubular inner formation 22 which has an external annular shoulder 23. The passage 21 leads to orifices 27 through a top wall of the formation 22.

The upper end 24 of the formation 22 provides an external cylindrical guide surface for an inner sleeve member 30 having an inwardly projecting annular shoulder 31. The shoulders 23 and 31 form a lost-motion connection between the valve member 14 and the sleeve member 31.

An operating stem 40 is screwed into an end wall 32 of the sleeve member 30. Orifices 33 extend through the wall 32 from the interior of the sleeve so as to provide with the passage 21 pressure balancing of the valve member 14. A compression spring 34 within the sleeve member 30 acts on it and on the valve member 14 in the sense of closing movement towards the seat 1 3.

The valve member 14 has an inner cavity 36 and a circumferential band of inlet ports 37 and the wall 1 9 and outlet ports 38 in the bottom wall 15.

The closure 28 is secured in a fluid-tight manner to the body 10 and the guide 29 extends through a bore 41 in the body 10. The closure 28 is secured by bolts 42, two only of which are shown. The bolts 42 also secure to the closure 28 ,a housing 43, which includes an upstanding chamber 44. The stem 40 extends through the end wall of the chamber 44 and is screwed at one end to the sleeve member 30 and at the other end to a collar 45. A valve operating lever 47 is connected at a pivot 49 to a link 46 and thence to the collar 45 and is mounted on a pivot 48. The valve member 14 is biased to the closed position by a compression spring 51, which is held between the collar 45 and cap 52, which is secured to the housing 43 by nuts and bolts 53, 54 two only of which are shown.

The passage 21 and the ports 27 and 33 provide pressure balancing to reduce the force required to be exerted on the stem 40 via the link 46 and the lever 47 to open and close the valve.

Operation Initially the valve member 1 4 is fully seated as shown in Figure 1, so that there is no fluid-flow between thg inlet port 11 and the outlet port 12.

The sequence of operation will be fully described below with reference to Figures 1,2 and 3.

In the closed position shown in Figure 1 high pressure fluid exists in the inlet 11 and in the the valve body 10 but flow to the outlet port 12 is blocked. The inlet ports 37 are closed by the sleeve member 30.

The valve is operated to allow the flow of highpressure fluid flow by an operating mechanism, not shown, which is attached by a pivot 50, to the lever 47 and which acts in the direction of the arrow x. This moves the link 46 upwards to compress the spring 51. The sleeve 30 is pulled upwardly by the stem 40 and progressively uncovers the inlet ports 37. This allows a controlled amount of high-pressure fluid to enter the cavity 36 and to flow through the outlet ports 38 into the outlet port 12. As the sleeve member 30 lifts, the spring 34 continues to push the valve member 14 into sealing engagement with the seat 13.

The sleeve member 30 continues to rise (with no movement of the valve member 14) until the shoulder 31 engages the shoulder 23, as shown in Figure 2. All lost motion has then occurred and the valve member 14 and the sleeve member 30 then rise together. The spring 34 maintains the shoulders 31 and 23 in the positive engagement.

As the valve member 14 continues to rise, the rim 18 leaves the seat 1 3 and the high pressure fluid flows past the seat 13 and is directed by the wall section 1 7 and the cylindrical shape at 1 6 to flow in an annular flow path. The dimensions of the parts are such as to ensure that, during valve opening the fluid flow adheres to the wall of seat 13 to produce an annular flow path.

The raising of the down-stream pressure by means of the initial fluid flow through the ports 37, the cavity 36 and the ports 38 assists in maintaining the annular flow. The transition from the fully-blocked to the partly-opened position is accomplished with a considerable reduction of noise and vibration.

As the valve member 14 is further lifted progressively toward the position shown in Figure 3, the valve becomes fully open and the flow remains in an annular path in the outlet port 12.

The inlet ports 37 are then progressively closed by the valve guide portion 29 until they are closed off completely and all the fluid flows unimpaired past the valve member 14 in the final fullyopened position as shown in Figure 3.

The very low pressure ratio now existing across the valve at full-lift ensures that the fluid-flow has insufficient energy to detach itself from the wall of outlet port 1 2 so that jet-flow interaction at the centre of the outlet port is minimal and noise and vibration are relatively slight.

A fluid damping arrangement, not shown, may be provided between the sleeve member 30 and valve member 14 in order to prevent flowinduced vibrations of either or both members under certain conditions of fluid-flow. The diameter of the ports 27 may be optimised for this purpose.

Claims

1. A steam turbine control valve comprising a hollow valve member movable within a hollow valve body which has an inlet port, an outlet port and a generally convex valve seat for co-operation with the valve member to block the flow of fluid past the valve member when the latter is seated, the valve member having a plurality of inlet ports up-stream of the seat which are progressively openable by movement of a further member relative to the valve member while the latter is seated and the valve member also having a plurality of outlet ports which open into the outlet port.

2. A valve according to claim 1, in which the valve member has a cavity defined in part by a flat bottom wall through which the outlet ports pass.

3. A valve according to claim 1 or claim 2, in which the inlet ports in one embodiment may be located in a cylindrical wall of the valve member and said further member is slidable within the valve member.

4. A valve according to any proceding claim, in which a pressure-balancing passage passes through the valve member to reduce the force required for valve operation.

5. A valve according to any preceding claim, in which a fluid damping arrangement is provided between the sleeve member and the valve member to prevent flow induced vibrations of either or both members.

6. A steam turbine control valve according to claim 1, substantially as hereinbefore described with reference to the accompanying drawings.