GB2104293A - Pressure detector - Google Patents

Abstract

A fluid pressure detector switch having a pair of electrical contacts (5a, 5b) with electrical conductors (3, 11) extending therefrom, an inner sealable container (1) having a wall portion which is deformable to operate the switch and which restores when the pressure is removed, and an outer sealable container (6) within which the inner sealable container (1) is positioned so that the electrical conductors (3, 11) extend from the switch contacts (5a, 5b) to a region external of the outer container (6), whereby in use of the detector switch both containers (1, 6) can be sealed so that a predetermined pressure differential normally obtains therebetween and so that a change of fluid pressure in the outer container (6) results in deformation of the wall portion of the inner container (1) and consequential operation of the switch contacts (5a, 5b) which is detectable externally of the detector across the said conductors (3, 11). <IMAGE>

Description

SPECIFICATION Pressure detector This invention relates to fluid pressure detectors usable more especially although not exclusively for the detection of mechanical stress.

Accordingly, this invention provides a fluid pressure detector comprising an electrical switch having a pair of electrical contacts with electrical conductors extending therefrom, an inner sealable container having a wall portion which is deformable to operate the switch and which restores when the pressure is removed, and an outer sealable container within which the inner sealable container is positioned so that the electrical conductors extend from the switch contacts to a region external of the outer container, whereby in use of the detector both containers can be sealed so that a predetermined pressure differential normally obtains therebetween and so that a change of fluid pressure in the outer container results in deformation of the wall portion of the inner container and consequential operation of the switch which is detectable externally of the detector across the said conductors.

The inner container may have an elastic wall deformable to bring together the pair of electrical contacts of the switch.

The inner container may comprise a rubber tube.

The inner container may have coupled to it an inlet/outlet tube which extends through a wall of the outer container and by means of which pressure in the inner container can be pre-set prior to closure of the inlet/outlet tube to seal the inner container.

The detector may include a further inlet/ outlet tube which communicates with the outer container and which facilitates setting of the pressure therein.

The two inlet/outlet tubes may be fabricated of electrically conductive material such as copper or some other metal and may comprise the said conductors.

The outer container may include a neck portion which is externally screw threaded at one end and which includes a passageway which communicates with the interior of the said outer container.

The detector may comprise a protective sleeve within which the two containers are housed.

The protective sleeve and/or the outer container may be fabricated of a rigid plastics material or of glass.

In accordance with one embodiment of the invention the inner and outer containers may be depressurised so that the interior of both containers are normally at substantially the same reduced pressure whereby no deformation of the said wall normally takes place, and whereby consequent upon return of the outer container to atmospheric pressure the wall of the inner container deforms thereby operating the switch to facilitate detection of the pressure increase.

The detector may be utilized to detect stress and for this purpose may be positioned and arranged such that stressful conditions are effective to produce a pressure differential between the pressures which obtain in the inner and outer containers respectively.

Thus it may be arranged that the stressful conditions are effective to cause air at atmospheric pressure to leak into the outer container whereby a pressure differential between the inner and outer containers is produced effective to operate the switch.

Embodiments of the invention will now be described solely by way of example with reference to the accompanying drawings in which: Figure 1 is a sectional view of a first pressure detector comprising a switch which is not operated; Figure 2 is a sectional view of the detector shown in Fig. 1 but in which the switch is in an operated condition; Figure 3 is a sectional view of a second pressure detector comprising a switch which is not operated; and Figure 4 is a sectional view of the detector shown in Fig. 3 but in which the switch is in an operated condition.

Referring now to Figs. 1 and 2, a first pressure detector comprises an inner container 1, made of rubber which is deformable but elastic so that it restores after deformation to its original shape, the container 1 being generally tubular and sealed at one end by means of a rubber stopper 2. The other end of the container 1 is tightly fitted to a metal tube 3 which is hermetically sealed at its end 4 remote from the inner container 1. Contained within the inner container 1 is a switch 5 comprising a pair of contacts 5a and 5b.

The rubber inner container 1 is contained within an outer container 6 defined by a rigid plastics tube, the end 4 of the metal tube 3 being arranged to extend through an end wall 6a of the outer container 6. The outer conainer 6 is tightly fitted to a neck part 7a, of a body portion 7 carrying on an end thereof remote from the neck 7a, a screw thread 8 and being bored to provide a passageway 9, which communicates with the interior of the outer container 6. Formed in the body portion 7 is side passage 10 which communicates with the passageway 9 and with a metal inlet/outlet tube 11. The metal tubes 3 and 11 are electrically connected to the contacts 5a and 5b by means of conductors 1 2 and 13 and the metal tube 11 at its end 1 5 is hermetically sealed.The inner container 1 and the outer container 6, are embraced by a protective rigid plastics sleeve 16, through which the ends 4 and 1 5 of the metal tubes 3 and 11 project.

In use of the detector, the screw threaded end 8 of the body 7 is screwed into the complementary threads of a bore in material in which stress is to be detected. The inner container 1 is then evacuated from the end 4 of the tube 3, so that the walls of the con tainer 1 are deformed inwardly and so that initially the contacts 5a and 5b are closed as shown in Fig. 2. The end 4 of the tube 3 is then hermetically sealed to preserve the va cuum, or partial vacuum, produced inside the inner container 1. By connecting a vacuum pump to the end 1 5 of the tube 11, the inside of the outer container 6 is then depressurised, so that the pressure therein corresponds to the reduced pressure within the inner container 1.The end 1 5 of the tube 11 is then hermetically sealed and since the pressures in the inner container and outer container are at this time substantially the same, the elastic rubber inner container 1 restores to its original shape as shown in Fig. 1 and the contacts 5a and 5b of the switch 5 spring apart. Any desired electrical circuit can then be connected between the metal tubes 3 and 11 and a desired alarm system. If due to stress, cracks develdop in the material within which the neck portion 8 is screwed, then the outer container will be depressurised and consequently the inner container will deform again due to the air pressure, and the contacts 5a and 5b of the swtiches will be brought together.The alarm system, which may be audio and/or visual, will then operate.

Referring now to Figs. 3 and 4, there is shown a second pressure detector in which similar parts as in Figs. 1 and 2 have been given the same reference numbers. The construction and operation of these parts will not again be given.

In Figs. 3 and 4, the tube 11 is provided in the chamber that surrounds the container 1.

The body portion 7 and its neck 7a then form the outer sealable container.

The body portion 7 and its neck 7a are made of metal and, because the rigid plastics tube 6 is omitted, the walls 7b of the body portion 7 and its neck 7a defining the chamber surrounding the tubes 1 and 11 are coated with an electrical insulation material.

The insulation material prevents short circuiting if, by accident, any part of the electrical circuit touches the wails 7b.

It is to be appreciated that the embodiments of the invention described above have been given by way of example only and that modifications may be effected. Thus, for example, in a further embodiment of the invention, not shown in the drawings, in order to detect movement between two bridge members, a glass end piece may be secured to the screw threaded end 8, and the glass end piece may be placed between the two bridge members. Consequent upon movement of one or other member towards the other, the glass end piece will be broken and the detector will be operated. Thus it will be appreciated that the detectors may be used for detecting stress in oil rig legs, in aircraft structures, bridges, pressure vessels, vacuum vessels and the like.

The detectors may be used beneath the sea, on land and/or in space and they may be primed with various inert gases as well as with atmospheric gases, although it will be appreciated that in accordance with a principal embodiment of the invention the two containers of the detector would normally be completely or almost completely evacuated.

Thus it will be appreciated that the detectors may be used to detect the in-rush of air in any airtight cavity.

Claims (10)

1. A fluid pressure detector comprising an electrical switch having a pair of electrical contacts with electrical conductors extending therefrom, an inner sealable container having a wall portion which is deformable to operate the switch and which restores when the pressure is removed, and an outer sealable container within which the inner sealable container is positioned so that the electrical conductors extend from the switch contacts to a region external of the outer container, whereby in use of the detector both containers can be sealed so that a predetermined pressure differential normally obtaines therebetween and so that a change of fluid pressure in the outer container results in deformation of the wall portion of the inner container and consequential operation of the switch which is detectable externally of the detector across the said conductors.

2. A fluid pressure detector according to claim 1 in which the inner container has an elastic wall deformable to bring together the pair of electrical contacts of the switch.

3. A fluid pressure detector according to claim 2 in which the inner container comprises a rubber tube.

4. A fluid pressure detector according to any one of the preceding claims in which the inner container has coupled to it an inlet/outlet tube which extends through a wall of the outer container and by means of which pressure in the inner container can be pre-set prior to closure of the inlet/outlet tube to seal the inner container.

5. A fluid pressure detector according to claim 4 and including a further inlet/outlet tube which communicates with the outer container and which facilitates setting of the pressure therein.

6. A fluid pressure detector according to claim 5 in which the two inlet/outlet tubes are fabricated of electrically conductive material and they comprise the said conductors.

7. A fluid pressure according to any one of the precding claims in which the outer container includes a neck portion which is externally screw threaded at one end and which includes a passageway which communicates with the interior of the said outer container.

8. A fluid pressure detector according to any one of the preceding claims and including a protective sleeve within which the two containers are housed.

9. A fluid pressure detector according to claim 8 in which the protective sleeve and/or the outer container are fabricated of a rigid plastics material or of glass.

10. A fluid pressure detector substantially as herein described with reference to the accompanying drawings.