GB2079409A

GB2079409A - Control valves for hot fluids

Info

Publication number: GB2079409A
Application number: GB8120627A
Authority: GB
Original assignee: Spirax Sarco Ltd
Current assignee: Spirax Sarco Ltd
Priority date: 1980-07-07
Filing date: 1981-07-03
Publication date: 1982-01-20
Also published as: GB2079409B

Abstract

A hot fluid flow control valve having a valve member (12) that is carried by an element (10) that flexes for moving the valve member to open or close the valve; the flexible element being subjected to vapour pressure of control fluid (11) that is heated by the controlled fluid, such that whilst the flow line fluid is at or below a predetermined temperature said vapour pressure is at a value determined by the temperature of the flow line fluid such that the valve is in one of an open or a closed state. For operating the valve, the vapour pressure is raised to flex the element (10) to move the valve member (12) to the other of said open or said closed state. In one form, for raising the vapour pressure, an electrical coil (16) is energised to heat a portion (11A) of the control fluid that is in its liquid state. In another form vapour pressure increase is achieved by physically displacing control fluid in its liquid state to a zone adjacent the flow line fluid so that the temperature of the displaced fluid is increased e.g. by use of an electric coil to move a core to displace fluid from a reservoir. <IMAGE>

Description

SPECIFICATION Control valves for hot fluids This invention relates to control valves for hot fluids.

Where a valve is to be used to control flow of a hot fluid, for example process steam, the high temperatures to which the valve is subjected impose restraints on, for example, solenoid valves.

According to the present invention there is provided a hot fluid flow control valve having a valve member that is carried by an element that flexes for moving the valve member to open or close the valve; the flexible element being subjected to vapour pressure of control fluid that is heated by the fluid, flow of which is to be controlled by the valve, such that whilst the flow line fluid is at or below a predetermined temperature said vapour pressure is at a value determined by the temperature of the flow line fluid such that the valve is in one of an open or a closed state; means being provided for raising said vapour pressure above said value thereby to flex the element to move the valve member to the other of said open or said closed state.In one particularform an electrical heating element is provided for increasing the vapour pressure by heating a portion of the control fluid that is in liquid state. In another form increase in vapour pressure is brought about by moving a displacement member of an electromagnetic assembly to displace control fluid in its liquid state from a zone remote from the flow line fluid to a zone close to the flow line fluid so that the temperature of the displaced control fluid is increased. Such a valve has a minimum of moving parts and moreover, since change in vapour pressure is utilised to effect controlled valve opening or closing, the mechanism for bringing about this change can be located remote from the flow line fluid which is at high temperature. Accordingly the number of valve parts subjected to the detrimental effects of high temperature is minimal.

Advantageously it can be arranged that if the valve is not operated by actuation of the mechanism for bringing about vapour pressure change, then operation is brought about automatically by increase in the vapour pressure caused by increase in the temperature of the flow line fluid to a temperature sufficiently above the predetermined temperature.

Four a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 is a diagrammatic illustration of a valve, shown open, and Figure 1A is an illustration of a modified form of the detail ringed at A in Figure 1.

Referring first to Figurel,the valve shown therein includes a casing 1 having an inlet port 2 and an outlet port 3 by which the valve can be connected in a fluid flow line such as a steam flow line, the port 3 being at the upper end of a hollow spigot 4 upstanding within the casing 1 from the base of the casing 1 and terminating, at the port 3, in a valve seat 5. Mounted on top of the casing lisa thermosyphon assembly 6 that consists of a lower chamber 7, an upright pipe 8 and an upper chamber 9. In the lower chamber 7 there is supported a bellows 10 such that the interior of the bellows is closed from the interior of the lower chamber 7, pipe 8 and upper chamber 9 but is open to the interior of the casing 1.Within the assembly 6 there is volatile fluid which collects as a small volume of volatile liquid 11 in the lower chamber 9, above which there is the vapour of the fluid, the volatile fluid in both liquid and vapour state being outside the bellows 10. A valve member 12 carried by the wall of the bellows 10 remote from the valve seat 5 passes through an aperture 13 in the opposite wall of the bellows 1,which aperture is sealed to the thermosyphon assembly 6 where the assembly supports the bellows.

The chamber 9 at the top of the pipe 8, and hence remote from the bellows 10, is a condenser chamber from which condenser fins 14 project and in the base of which there is an annular reservoir 15. This reservoir 15 is provided with a heating coil 16 and contains a small additional volume of the volatile fluid collected as liquid 11A.

In use of this valve at low ambient temperatures at which the valve pressure within the thermosyphon assembly 6 is low, the bellows 10 is in its relaxed condition in which the valve member 12 is clear of the seat 5 and the valve 10 is open (Figure 1). The main volume of volatile fluid that is in liquid state, that is the liquid 11 collected in the lower chamber 7, will be heated and vapourised by hot fluid flowing in the flow line controlled by the valve, this hot fluid entering the bellows 12 through the aperture 13, but provided the temperature of the hot fluid is at or below a predetermined value insufficient pressure builds up within the thermosyphon to close the valve.From this condition the valve can be closed by energising the heating coil 16 to heat up and vapourise the additional volume of volatile fluid in liquid state, that is the liquid 11A, that is in the resevoir 15 at the top of the thermosyphon assembly 6, and thereby the vapour pressure is increased sufficiently to move the upper wall of the bellows 10 down to cause the valve member 12 to seat on the seat 5 and close the valve.

To open the valve the heating coil 16 is deenergised. Volatile fluid condenses on the walls of the upper chamber 9 and runs down these walls to collect again as liquid 1 in the reservoir 15 whilst the vapour pressure drops. This vapour pressure drop allows the bellows to expand and the valve opens.

In Figure 1, 17 is a stop limiting movement of the upper bellows wall in the directon away from the valve seat 5.

It is to be noted that the major part of the heat that is required to raise the vapour pressure sufficiently to close the valve is obtained from the hot fluid, flow of which is to be controlled. Only a relatively small amount of extra heat has to be provided, by energising the heating coil 16, when it is desired to close the valve. Thus the current required to energise.the heating coil 16 to close the valve is small.

Furthermore, the heating coil 46 and components associated therewith such as a switch are located remote from the hot flow line fluid and only the lower part of the thermosyphon assembly 6, and the bellows 10 and its valve member 12, have to be close to the hot fluid line fluid.

It will be recognised that in the valve just described the bellows 10 with the volatile fluid associated therewith is a so-called "balance pressure bellows element". By combining this component with the thermosyphon assembly 6 there is obtained a valve that is not only well suited for use in controlling flow of hot fluids as it utilises the heat of the flow line fluid in its operation and therefore the further energy that has to be provided to actuate the valve is minimised, but furthermore the number of moving components is minimal, as is the number of components subjected to the detrimental effects of the high temperature of the hot fluid.

In the modification of Figure 1A, the heating coil of Figure 1 is replaced by a displacement member 18 of an electromagnetic assembly, and the reservoir 15 is enlarged such that it can contain the whole of the volatile fluid in its liquid state. Energisation of a coil 19 of this electromagnetic assembly moves the displacement member 18 from a position clear of the annular reservoir 15 (full lines in Figure 1A) into the reservoir (dotted lines) thereby to displace liquid from the reservoir. The liquid thus displaced to the zone of the bellows 10 is heated by the fluid in the flow line and the vapour pressure in the thermosyphon assembly 6 increases so that the valve closes. By moving the member 18 out of the annular reservoir 15 again, condensed liquid again collects therein, the vapour pressure drops and the valve opens.

In the above there has been described operation of the valve effected by actuation of the heating coil 16 (Figure 1) or of the electromagnetic assembly 18/19 (Figure 1A) when the temperature of the flow line fluid being controlled is no higher than a predetermined value. It can be further arranged that should the valve not be so operated, and should the flow line fluid temperature rise sufficiently far above this predetermined value, then the resultant further increase in vapour pressure is sufficient to bring about automatic operation of the valve without actuation of the coil 16 or electromagnetic assembly 18i19.

Furthermore it can be arranged that the valve is normally closed and is opened by sufficient increase in vapour pressure within the pipe 8.

Claims

1. A hot fluid flow control valve having a valve member that is carried by an element that flexes for moving the valve member to open or close the valve; the flexible element being subjected to vapour pressure of control fluid that is heated by the fluid, flow of which is to be controlled by the valve, such that whilst the flow line fluid is at or below a predetermined temperature said vapour pressure is at a value determined by the temperature of the flow line fluid such that the valve is in one of an open or a closed state; means being provided for raising said vapour pressure above said value thereof thereby to flex the element to move the valve member to the other of said open or said closed state.

2. A valve as claimed in claim 1, wherein the flexible element is a balanced pressure bellows element one side of which is exposed to the vapour pressure of the control fluid an the other side of which is exposed to the flow line fluid pressure.

3. A valve as claimed in claim 2, wherein said means is a thermosyphon assembly in which a pipe containing the control fluid is disposed on said one' side of the bellows element so as to be upright in use.

4. A valve as claimed in claim 3, wherein displaced from the foot of the pipe is a condenser chamber that includes a reservoir that has a capacity such as to collect some but not all of the control fluid that is in liquid state when the vapour pressure is at said value, and wherein there is provided means for heating the control fluid in liquid state collected in this reservoir thereby to increase the vapour pressure above said value.

5. Avalve as claimed in claim 4, wherein the heating means is an electrical heating element in the reservoir.

6. A valve as claimed in claim 3, wherein displaced from the foot of the pipe is a condenser chamber that includes a reservoir that has a capacity such as to collect all the control fluid that is in liquid state when the vapour pressure is at said value, and wherein means is provided for displacing liquid from this reservoir so that the displaced liquid can pass to the foot of the pipe to bevapourised by heat from the flow line fluid.

7. A valve as claimed in claim 6, wherein the displacing means is a displacement member of an electromagnetic assembly.

8. A hot fluid flow control valve substantially as hereinbefore described with reference to Figure 1 or Figure 1A of the accompanying drawing.