GB2123529A - A pressure regulator - Google Patents

Abstract

A device for regulating the pressure of a gas in a glove box comprises a resiliently biassed pressure sensitive diaphragm 22 and a spool valve operable by deflection of the diaphragm. The diaphragm is arranged to be exposed on one side to atmospheric pressure and on the other side to the pressure of the gas in the glove box, and the spool valve 10 is used to control simultaneously the rates at which gas is pumped in and out of the glove box. The valve spool 44 has two axially spaced circumferential grooves 86, 88 which provide communication between conduits 80, 81 and 82, 83 respectively, the flow control along each path being effected by means of apertures 90, 91, 92, 93 in a sleeve 40 within which the spool slides. <IMAGE>

Description

SPECIFICATION A pressure regulator The invention relates to devices for regulating the pressure of a gas inside a containment, for example a glove box. A glove box is a chamber within which work can be carried out on materials such as viruses, toxic chemicals, or radioactive materials, holes being provided through a side of the chamber each sealed by a rubber glove so as to enable an operator to insert his hands into the chamber inside the gloves to work on the materials.

It is usual to pump a gas continuously into and out of the glove box, while maintaining the pressure inside the glove box slightly below atmospheric pressure, so that any leakage, if it were to occur, would cause gas to flow into the glove box from the surroundings, inhibiting release of the materials from the glove box. Conventional pressure regulators are relatively bulky and inconvenient to replace or service.

The invention therefore provides a device for regulating the pressure of a gas in a glove box, comprising a resiliently biassed pressure sensitive diaphragm arranged to be exposed on one side to the pressure of the gas in the glove box and on the other side to atmospheric pressure and a spool valve means comprising a spool slidable in a cylindrical valve chamber and operable by deflection of the diaphragm, the valve chamber defining two axially displaced pairs of adjacent ports, the first pair being adapted to communicate with the glove box and with a gas supply means respectively, and the second pair being adapted to communicate with the glove box and a gas extract means respectively, and the spool having two circumferential grooves in the surface thereof cooperating with the pairs of adjacent ports, thereby in operation controlling simultaneous gas flows into and out of the glove box.

The resilient biassing may be provided by spring means in the spool valve means remote from the diaphragm, and the resilient biassing force may be adjustable so as to set a required value of pressure inside the glove box. Desirably, means are provided to damp the motion of the spool in the spool valve means.

The invention will now be further described by way of example only and with reference to the accompanying drawings in which: Figure 1 shows a side view in medial section of a pressure regulating device; Figure 2 shows a sectional view along the line Il-Il of Figure 1; and Figure 3 shows a side view in medial section of an alternative pressure regulating device.

In the above Figures, like parts have like numerals.

Referring to Figure 1, a pressure regulating device for a glove box comprises a spool valve means in the form of a valve assembly 10 and a pressure chamber 1 2. The pressure chamber 12 comprises a circular dish 1 4 with a peripheral flange 1 6 at its open end, and a circular protective cover 1 8 with a peripheral flange 20. A circular flexible membrane 22 of neoprene rubber is clamped between the flange 1 6 and the flange 20.

A hole 24 through the centre of the cover 1 8 ensures that the side of the membrane 22 nearer to the cover 1 8 is exposed to atmospheric pressure, and a pipe 26 extending from a port 28 in the dish 14 to the glove box (not shown) ensures that the other side of the membrane 22 is at the same pressure as gas in the glove box.

The valve assembly 10 includes a stainless steel tube 40, one end of which passes through a circular hole 42 in the dish 14. A valve rod 44 of molybdenum disulphide loaded nylon fits slidably inside the tube 40, one end of the valve rod 44 being clamped to the membrane 22 by two circular pressure plates 46 and 48 on either side of the membrane 22, and by a screw 50 through the centre of the pressure plates 46 and 48 and the membrane 22.

The other end 45 of the valve rod 44 is chamfered, and abuts a molybdenum disulphideloaded nylon follower plug 52 biassed into contact with the valve rod 44 by a helical compression spring 54 between the follower plug 52 and a seal plug 56. An O-ring seal 58 locates in a groove 60 around the outside of the seal plug 56. The position of the seal plug 56 in the tube 40 may be adjusted by means of a set screw 62 and lock nut 64, the set screw 62 abutting the seal plug 56 and passing through a threaded hole 66 in a square aluminium end plate 68.

The valve assembly 10 also includes five injection-moulded unplasticised polyvinyl chloride blocks 70, 71, 72, 73 and 74, square in crosssection, and clamped together by long bolts 76 extending between the end plate 68, through the blocks 70 to 74 and the dish 14 and engaging an aluminium end member 78 in the dish 14, the blocks 70 to 74 defining a circular bore 38 to accommodate the tube 40. The end member 78 abuts the base of the dish 14 and has a stepped bore 36 to locate the tube 40 and to allow the valve rod 44 to pass through. An O-ring seal 95 locates in a groove 96 on one face of each block 70 to 74 and of the end member 78, and an O-ring seal 97 locates in a chamfered end 98 of the bore 38 abutting both the tube 40 and the end plate 68.

At two places along its length the valve rod 44 is reduced in diameter to form two wide circumferential grooves 86 and 88. When the valve rod 44 is in the position shown, then each groove 86, 88 communicates with two axially displaced sets of holes 90 and 91, and 92 and 93 respectively, through the wall of the tube 40. The edges of the grooves 86 and 88 are shaped so that movement of the valve rod 44 to obstruct the sets of holes 90 and 92, or 91 and 93, causes a sharp cut-off to the flow of gas therethrough. As shown in Figure 2 the set of holes 93 consists of three equi-spaced circumferential slits, as do the sets of holes 90, 91 and 92.Each of the four blocks 70, 71,72 and 73 is partially relieved to form an annular chamber 100,101,102 and 103 respectively around the tube 40, each chamber 100, 101, 102 and 103 communicating with a respective set of holes 90, 91, 92 and 93 and also communicating with a respective tube 80, 81, 82 and 83. Each tube 80 to 83 has a respective enlarged end 110,111,112 or 113, locating in a respective close-fitting hole 120, 121, 122 or 123 in the respective block 70 to 73.

The tubes 80 and 83 are connected to the glove box, the tube 81 is connected to a gas supply (not shown), and the tube 82 is connected to an extract pump (not shown).

In operation of the pressure regulating device when the pressure in the glove box is at a desired value (typically about 30 mm of water (300 Pa) below atmospheric pressure), the valve rod 44 will be as shown in Figure 1. Gas will flow from the supply through the tube 81, the chamber 101, the set of holes 91, the groove 86, the set of holes 90, the chamber 100 and the tube 80 into the glove box, while at the same time and at the same rate gas will flow out of the glove box through the tube 83, the chamber 103, the set of holes 93, the groove 88, the set of holes 92, the chamber 102 and the tube 82 to the extract pump. The position of the valve rod 44 is determined by the balance between the force on the pressure plate 46 due to the difference in pressure between the two sides of the membrane 22, and the resilient force due to compression of the helical spring 54.Hence if the pressure in the glove box drops below the desired value then the force on the pressure plate 46 will increase and the valve rod 44 will move so as to compress the spring 54 more. This will change the position of the groove 86 with respect to the sets of holes 90 and 91 so as to increase the rate of gas flow into the glove box, and will change the position of the groove 88 with respect to the sets of holes 92 and 93 so as to decrease the rate at which gas is extracted from the glove box. The pressure in the glove box will thus be raised back to the desired value. On the other hand, if the pressure in the glove box rises above the desired value, the force on the valve rod 44 due to the spring 54 will exceed the force on the pressure plate 46, and so the valve rod 44 will move so as to reduce the compression of the spring 54.This will increase the flow rate of gas out of the glove box through the groove 88 and the sets of holes 93 and 92, while decreasing the rate at which gas is supplied to the glove box through the groove 86 and the sets of holes 91 and 90, so decreasing the gas pressure in the glove box to the desired value.

Thus the pressure regulating device controls the pressure in the glove box. The rates of flow of gas through the pressure regulating device with the glove box pressure at the desired value may be adjusted by external valves (not shown), and typically might be between 1 and 100 litres/min.

The desired value may be changed by adjusting the set screw 62 so as to change the position of the seal plug 56, so changing the degree to which the spring 54 is compressed when equilibrium is reached between the rates at which gas is supplied to the glove box and extracted from it.

The motion of the valve rod 44 as described above is damped by means of a narrow groove 105 (shown enlarged in Figure 2 for clarity) along the surface of the valve rod 44 between the groove 88 and the chamfered end 45 of the valve rod 44. Because the follower plug 52 does not have a gas-tight seal around its edge, the narrow groove 105 enables gas to flow between the groove 88 and the space defined by the tube 40, the follower plug 52 and the seal plug 56, as the valve rod 44 moves in the tube 40. The restriction to gas flow imposed by the narrow groove 105 provides significant damping to the valve rod 44.

Alternatively, the damping of the motion of the valve rod 44 may be brought about by providing a relatively small hole 24 in the cover 1 8 (i.e.

smaller than that shown in Figure 1), the groove 105 being dispensed with.

Although the blocks 70, 71,72, 73 and 74 have been described as being clamped together with O-rings 95 between them, it will be understood that other methods of construction may be adopted. For example in Figure 3 is shown an alternative pressure regulating device similar to that shown in Figure 1, comprising a valve assembly 1 50 and a pressure chamber 12. The pressure chamber 12 differs from that of Figure 1 in having a smaller hole 24 through a protective cover 1 8. The valve assembly 1 50 incorporates a valve rod 160 of molybdenum disulphide-loaded nylon which fits slidably inside a tube 40 and is clamped at one end to a membrane 22 within the pressure chamber 12.The valve rod 160 is reduced in diameter at an intermediate position along its length to form a circumferential groove 86, and is reduced in diameter along an end portion remote from the pressure chamber 12 so as to define a circumferential chamber 1 62 between the valve rod 1 60 and the tube 40. The groove 86 and the chamber 162 communicate, when the valve rod 1 60 is in the position shown, with two axially displaced sets of holes 90 and 91, and 92 and 93 respectively, through the wall of the tube 40.The tube 40 is accommodated within a bore 38 defined by five unplasticised polyvinyl chloride blocks 170, 171, 172, 173 and 174, circular in cross-section and solvent welded together, one end of the tube 40 being located by a circular end member 178 within the pressure chamber 12 and the other end of the tube 40 abutting a circular end plate 1 68. The end member 1 78 is attached by means of countersunk screws (not shown) engaging in threaded inserts (not shown) in the block 170, and the end plate 1 68 is attached by screws 176 engaging in threaded inserts (not shown) in the block 1 74. The end of the valve rod 1 60 remote from the pressure chamber 12 is located in a cylindrical recess 1 64 in a molybdenum disulphide-loaded nylon follower plug 1 66 biassed into contact with the valve rod 1 60 by a helical compression spring 54 between the follower plug 1 66 and a seal plug 56. In all other respects the pressure regulating device of Figure 3 is the same as that of Figure 1, and the two devices control the pressure in a glove box in the same manner.

It will be understood that the valve rod 1 60 and follower plug 1 66 of Figure 3 may be used in place of the valve rod 44 and follower plug 52 of Figure 1 and vice versa, the motion of the valve rod 1 60 being damped by the provision of a sufficiently small hole 24 in the cover 18. It will also be appreciated that there is always a certain degree of damping provided by friction between the valve rod 44 or 160 and the tube 40, and that in some circumstances this alone may damp the motion of the valve rod 44 or 1 60 adequately.

It will further be understood that alternative materials may be used in the pressure regulating devices of Figure 1 and Figure 3, for example the blocks 70-74 and 170-1 74 may comprise polymethylmethacrylate.

It will be appreciated that the response of the pressure regulating device to pressure changes in the glove box may be modified by replacing the circumferential slits, defining one of the sets of holes 90, 91, 92 or 93, by for example a circumferentially disposed set of circular holes, or by a plurality of sets of circumferentially disposed holes in which the holes of adjacent sets might be in staggered relationship, or by a set of two different diameter circular holes arranged alternately around the circumference and each having one edge tangential to a common plane perpendicular to the longitudinal axis of the tube 40.

Claims (9)

1. A glove box pressure regulator comprising a resiliently biassed pressure sensitive diaphragm arranged to be exposed on one side to the pressure of the gas in the glove box and on the other side to atmospheric pressure, and a spool valve means comprising a spool slidable in a cylindrical valve chamber and operable by deflection of the diaphragm, the valve chamber defining two axially displaced pairs of adjacent ports, the first pair being adapted to communicate with the glove box and with a gas supply means respectively, and the second pair being adapted to communicate with the glove box and with a gas extract means respectively, and the spool having two circumferential grooves in the surface thereof cooperating with the pairs of adjacent ports, thereby in operation controlling simultaneous gas flows into and out of the glove box.

2. A regulator as claimed in Claim 1 wherein the ports are defined by circumferential slits through the wall of the valve chamber.

3. A regulator as claimed in Claim 1 or Claim 2, wherein the spool valve means includes a spring means remote from the diaphragm to provide the resilient biassing force on the diaphragm.

4. A regulator as claimed in any one of the preceding claims, including means for adjusting the resilient biassing force.

5. A regulator as claimed in any one of the preceding claims, wherein the diaphragm comprises a rigid central portion and an annular flexible membrane portion attached to the central portion.

6. A regulator as claimed in any one of the preceding claims, including damping means to damp the motion of the spool.

7. A regulator as claimed in Claim 6 wherein the damping means comprises means to restrict air flow to that side of the diaphragm exposed to atmospheric pressure.

8. A regulator as claimed in Claim 6 wherein the damping means comprises a narrow axially extending duct in the spool valve means communicating with the end of the spool remote from the diaphragm.

9. A regulator substantially as hereinbefore described and with reference to Figures 1 and 2, or modified as described with reference to Figure 3, of the accompanying drawings.