GB2112114A

GB2112114A - Valve for cooling apparatus

Info

Publication number: GB2112114A
Application number: GB08235314A
Authority: GB
Inventors: Dennis Slow
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1981-12-21
Filing date: 1982-12-15
Publication date: 1983-07-13

Abstract

A valve includes a valve body 1, having an outlet orifice 6, a needle 3 mounted at the end of a bellows arrangement 4 which expand and contract to move the needle 3 to vary the effective aperture of orifice 6 as a function of temperature. A support plate 9 acts as a guide for needle 3, preventing lateral movement due to applied shock. <IMAGE>

Description

SPECIFICATION Improvements in or relating to valve arrangements This invention relates to improvements in valve arrangements and particularly to valves in cooling apparatus utilised for the cooling of a detector sensitive to electromagnetic radiation and especially to such radiation in the infra-red wave band.

In such coolers a source of gas under pressure is connected to and passed through a coil of tubing which surrounds a member forming a support for a chamber upon which the detector is mounted, said member and chamber being cooled as a result of the JOULE-THOMPSON effect. The open end of said tubing is restricted by a needle valve under control of a bellows whereby the flow of liquified gas issuing from the end of the tubing is controlled whereby the level of resulting liquid in the chamber is held substantially constant.

In present cooler assemblies the valve body is rigidly mounted upon a member attached to the casing surrounding the assembly and the needle is supported at the end of a bellows arrangement.

The needle of the valve is not laterally constrained except when the pointed end is in contact with the orifice. Such a condition may exist when the cooler is in store or when it is not in the operative condition. In use, the needle is moved back and forth with respect to the valve body to vary the effective aperture of the valve by virtue of thermal expansion or contraction of the bellows, so that the temperature in the chamber is maintained at a constant degree.

It has been found that with this present arrangement, any shock loads in handling the cooler assembly or of the body of the unit in which said cooler is located, results in the end of the needle valve breaking off.

While it may be thought advantageous to increase the valve seat angle, thereby to increase the conical cross-sectional area of the valve, with such an existing design this results in the acceptable lateral displacement under shock being reduced and the needle then leaves the orifice on opening and impinges upon the orifice side on closure.

Such an increase in angle may also result in any lateral displacement due to shock being translated into a greater axial displacement by virtue of the conical surface riding up over a lip of the orifice.

According to one aspect of this invention, there is provided a valve arrangement including a valve body having an orifice through which fluid may flow, a valve member having a main body portion of generally elongate form and an end portion of generally conical form, said valve member being movable longitudinally with respect to said orifice to effect control of the fluid flow therethrough, and valve member support means arranged adjacent said orifice ot prevent lateral movement of the valve member.

Preferably, said valve member support means includes an aperture arranged coaxially with the orifice and arranged slidably to receive at least part of the main body portion of the valve member, one of the valve support means and the yalve member including passage means through which fluid may flow after leaving the orifice.

Figure 1 a shows in diagrammatic form a part section of a cooling device which includes an existing form of valve arrangement; Figure 1 b shows in diagrammatic form a part section of a cooling device which includes a valve arrangement constructed in accordance with this invention.

Figures 2a and 2b show enlarged views of parts of one embodiment of a valve arrangement constructed in accordance with this invention, Figure 2a being a view upon Arrows A and A' of Figures 1 b and 2h, respectively, and Figure 3 shows enlarged views of a second embodiment of valve arrangement constructed in accordance with this invention.

In Figure 1 a housing 1 is supplied with air under pressure through Port 2, a needle 3 being mounted at the end of a bellows arrangement 4 which expand and contract under the influence of the temperature in compartment 5 to move the needle 3 back and forth and thus vary the effective area of the orifice 6 and in this manner to regulate the flow of air out of said housing via orifice 6 into compartment 5. The arrangement is such that in the static condition the needle valve allows a very restricted flow path through orifice 6. As the air issues through orifice 6, it expands and, due to the JOUSE-THOMPSON effect, the temperature thereof is reduced.This cold air is recircled by means not shown to further cool the incoming air with the result that liquid air eventually forms in compartment 5 and serves to cool a radiation sensitive detector 7 which is secured to the insulating wall 8 of the device.

It is arranged that the flow path through orifice 6 is regulated by the effect of temperature effectively causing relative displacement of needle 3 and housing 1, whereby the detector is supplied with a sufficient quantity of liquid air consistent with minimum air consumption.

However, the arrangement shown in Figure 1 a suffers from the disadvantage that due to the very small diameter of the needle (.018") lateral shock gives rise to fracture of the needle cone.

If the needle cone angle is made smaller, this increases the lateral stability though the strength is decreased. At the other extreme, if the cone angle is maximised then the needle valve may be forced out of the orifice.

Referring to Figure ib, these problems are overcome by introducing a support plate 9 to act as a guide. One form of such support plate is shown in Figures 2a and 2b, said plate being located in position by use of a dummy needle and when in position then secured to the valve housing by LOCTITE IS 1 2 adhesive.

The plate 9 includes a central bore 10 which slidably receives the needle 3, and three passageways 11 communicating with the bore 10 which allow fluid passing through the orifice to flow into compartment 5. Instead of providing a separate support plate 9, the nozzle orifice and central bore 10 may be formed in a single block using a Slocombe type drill.

In a second embodiment shown in Figure 3, the valve orifice and central bore 10 are formed in a single blosk and the needle 3 is provided with three passageways in the form of flats 12 ground on its sides. In this second embodiment, it may be necessary to use a larger diameter needle 3 to compensate for the flats 1 2.

Tests to discover the effect of lateral displacement showed that the modification provides adequate protection up to 200G and demonstrated that a range of cone angles could be accommodated.

Claims

1. A valve arrangement including a valve body having an orifice through which fluid may flow, a valve member having a main body portion of generally elongate form and an end portion of generally conical form, said valve member being movable longitudinally with respect to said orifice to effect control of the fluid flow therethrough, and valve member support means arranged adjacent said orifice to prevent lateral movement of the valve member.

2. A valve arrangement according to Claim 1, wherein said valve member support means includes a bore arranged co-axially with the orifice and arranged slidably to receive at least part of the main body portion of the valve member, one of the valve support means and the valve member including passage means through which fluid may flow after leaving the orifice.

3. A valve arrangement according to Claim 2, wherein the bore of the valve member support means is generally cylindrical, and the main body ,portion of the valve is generally cylindrical but with one or more longitudinally extending flats provided on its surface to provide said passage means.

4. A valve arrangement according to Claim 2, wherein the bore of the valve member support means is generally cylindrical but which one or more longitudinally extending channels provided therein to define said passage means and the main body portion is generally cylindrical.

5. A valve arrangement according to any of the preceding Claims wherein the valve member is mounted with respect to the valve body by means of a support member adapted to expand and contract to effect longitudinal movement of the valve member under the influence of the temperature of the fluid issuing through the orifice.

6. A valve arrangement, substantially as hereinbefore described with reference to and as illustrated in, any of Figures 1 b to 3 of the accompanying drawings.