GB2224844A - Pressure gauge testing - Google Patents

Abstract

A pressure gauge testing device, e.g. for checking that a mechanical pressure indicator of a fire extinguisher is not stuck in place, comprises a piston (4) with an axial bore 7 a cylinder (5) and a seal (11). The testing device is applied to the gauge (2) and air forced from the device into the gauge. If the gauge is not stuck, the pointer will move towards zero when the compressed air is applied and then revert to its original position when the externally applied pressure is removed. <IMAGE>

Description

PRESSURE GAUGE TESTING This invention relates to a pressure gauge testing device, and it relates in particular to such a device as may be used for checking that a mechanical indicator member, forming part of a gauge attached to and indicating the pressure of the contents of a reservoir, is not stuck in place.

In circumstances for example where a gauge, perianently attached to apparatus including a reservoir containing pressurised fluid, is intended to convey a reliable indication as to the pressure of said fluid and hence the operational condition of the apparatus, and where the gauge relies upon a mechanical movement, for example of a pointer relative to a scale, to indicate the aforesaid pressure, it is important to check from time to time that the pointer has not become stuck in place, thus indicating an acceptable pressure whereas in fact the pressure lay have fallen to an unacceptable level. This is particularly the case with apparatus that may be used to save lives, andlor protect valuable property, such as a fire extinguisher.Indeed, it is a requirement of the British Standard covering the servicing of such extinguishers that the annual service of such apparatus must include a check upon the freedom of movement of such mechanical indicators.

It has been proposed that the freedom of movement be checked by applying an external pressure to the gauge components, tending to balance the pressure applied to those components by the fluid in the reservoir. To this end, compressed air is introduced into the gauge through a vent hole formed in the glass or other transparent material covering the gauge. If the gauge is not stuck, the pointer will move towards zero when the compressed air is applied and then revert to its original position when the externally applied pressure is removed.

Prior techniques for applying the aforementioned external pressure have involved clamping an adaptor to the gauge and introducing compressed air through the vent hole. The compressed air is supplied either from a foot pump or a gas bottle, giving rise to the difficulties that the equipment is quite expensive and bulky for an engineer to transport.

This invention aims at providing a pressure gauge testing device which operates on the principle described hereinbefore and which overcomes, or at least reduces, the aforementioned difficulties.

According to the invention there is provided a pressure gauge testing device comprising a rod member and a sleeve member disposed for relative axial movement therealong and closed at one end, one end of the rod member being disposed within said sleeve member and forming with said one end of said sleeve member a cavity the volume of which can be changed by sliding said sleeve member relative to said rod member, said rod member being formed with an axially directed aperture passing completely therethrough, comnunicating between said cavity and an opening at the end of said rod member remote from said sleeve member, a first annular seal member surrounding said opening and a second annular seal member disposed between said rod member and said sleeve member to render said compartment substantially airtight except through said aperture, the diameter of said first seal being less than that of said second seal and the reduction of the volume of said cavity by axial sliding motion of said sleeve member along said rod member towards the end thereof bearing said first annual seal being capable of forcing air out of said opening in said rod member and into a gauge to be tested.

In order that the invention may be clearly understood and readily carried into effect, one embodiment thereof will now be described with reference to the accompanying drawings of which: Figure 1 shows a device in accordance with one example of the invention being employed to check a gauge attached to a fire extinguisher, Figure 2 shows, partly in side elevation and partly in section, the device of Figure 1, and Figure 3 shows a schematic axial cross-section through a device in accordance with one example of the invention, illustrating how the device is rendered self-sealing to a surface of the gauge under test.

Referring now to the drawings, similar components in all of which are identified by common reference numbers, Figure 1 shows a device 1, in accordance with one example of the invention, being used to check a gauge 2 of a fire-extinguisher 3 for freedom of mechanical movement.

The device 1 comprises two basic components, an inner insert, or rod member 4, which remains static in use during pressure testing, and an outer sleeve or cylinder member 5, closed at one end 6, which can slide axially relative to the member 4. The rod member 4 has an axial bore 7 passing completely through it and opening at one end into a chamber 8 within the cylinder member 5. Bore 7 is also open at its other end, forming an air outlet 9 for the device, through which air can be injected into the vent hole 10 (Figure 3) in the glass or other transparent covering of the gauge 2.

The air outlet 9 is surrounded by a first annular seal 11, of relatively small diameter, which is intended to provide an air-tight seal between the device and the glass or other transparent covering of the gauge 2 and to encircle the vent hole 10. Seal 11 is made of a suitable resilient material and is affixed to the rod member 4.

A second annular seal 12, of relatively large diameter, is disposed between the sleeve member 5 and the rod member 4. The seal 12 is captive in an annular groove 13 near the open end 14 of the sleeve member 5, and the end of rod member 4 which communicates with chamber 8 is formed with a retaining configuration 15 consisting of a groove 15a and a ridge 15b which are suitably configured and dimensioned to form a detent, preventing the rod member 4 from accidentally falling out of or being withdrawn from the sleeve member 5.

That part of the rod member 4 which protudes from the sleeve member when the device is compressed is formed with a groove 16 having a lip 17 of significant dimensions which enables the rod member 4 to be readily withdrawn by hand to an extended position in which the detent formed by the elements 15a and 15b interlocks with seal 12.

In use, the device 1 is extended and then applied by hand to the gauge 2 so that the seal 11 surrounds the vent hole 10.

The sleeve member 5 is then pushed by hand towards the gauge so that it slides along the rod member 4. This reduces the size of the chamber 8, forcing the air therefrom along the bore 7 and out of the outlet 9, thus through the vent hole 10 into the gauge to tend to balance the force applied to the gauge 2 from within the extinguisher 3. The pointer of the gauge, if it is working properly, will deflect towards zero and then reassume its original position when the device 1 is removed.

Whilst in operation, the device 1 effectively seals itself to the gauge by virtue of its construction and in particular the relative diameters of the two annular seals 11 and 12. The forces holding the seal 11 to the gauge being given approximately by the force applied minus the force attempting to separate the seal and the gauge. Hence the force holding the seal to the gauge is given by the expression: S = F - F x (Diameter of seal 11)2 (Diameter of seal 12)2 where F is the force used to slide member 5 along rod 4.

Thus it can be observed that the holding force would be zero if the diameters of the two seals were equal and would be negative, i.e. a force disturbing contact between the device 1 and the gauge 2 if the diameter of seal 11 were to exceed that of seal 12.

For reasons including that, due for example to manufacturing tolerances in the seals andlor the components to which they relate, it is considered prudent to ensure that the inner diameter of seal 12 exceeds significantly the outer diameter of seal 11. In one practical example, these diameters were 24.6In and 12mm respectively. In the example, the inner - diameter of seal 11 was 8mm.

The sleeve member 5 typically is of length 65-n (excluding the axial extent of the domed end closure at 6) and has an inner diameter of 25-n and an outer diameter of 31mm. It is typically, though not of course necessarily, made of aluminium.

The rod member 4 is typically made of plastics material such as Black Nylon 6 and, in one example, it is of overall length 77In. The diameter of bore 7 is 2.5mm and the outside diameter of rod member 4 is 24.9mm.

Claims (6)

1. A pressure gauge testing device comprising a rod member and a sleeve member disposed for relative axial movement therealong and closed at one end, one end of the rod member being disposed within said sleeve member and forming with said one end of said sleeve member a cavity the volume of which can be changed by sliding said sleeve member relative to said rod member, said rod member being formed with an axially directed aperture passing completely therethrough, communicating between said cavity and an opening at the end of said rod member remote from said sleeve member, a first annular seal member surrounding said opening and a second annular seal member disposed between said rod member and said sleeve member to render said compartment substantially airtight except through said aperture, the diameter of said first seal being less than that of said second seal and the reduction of the volume of said cavity by axial eliding motion of said sleeve member along said rod member towards the end thereof bearing said first annual seal being capable of forcing air out of said opening in said rod member and into a gauge to be tested.

2. A pressure gauge testing device according to Claim 1 wherein the rod member has means such that when the device is compressed, a part of the rod member protrudes such that the rod member may be readily withdrawn to an extended position.

3. A pressure gauge testing device according to Claims 1 or 2 wherein the end of the rod member which communicates with the chamber is formed with a retaining configuration such that the rod member cannot be withdrawn from the sleeve member.

4. A pressure gauge testing device as claimed in Claims 1 to 3 wherein the rod member is made of a plastics material.

5. A pressure gauge testing device according to Claims 1 to 3 wherein the sleeve member is made of aluminium.

6. A pressure gauge testing device substantially as hereinbefore described by reference to the accompanying drawings.