GB2310538A

GB2310538A - Fluid flow detection device

Info

Publication number: GB2310538A
Application number: GB9702723A
Authority: GB
Inventors: Mark Hayles
Original assignee: Elfab Ltd
Current assignee: Elfab Ltd
Priority date: 1996-02-20
Filing date: 1997-02-11
Publication date: 1997-08-27
Also published as: GB9603489D0; GB9702723D0

Abstract

A fluid flow detection device, particularly for detecting fluid flow resulting from rupture of pressure sensitive devices such as bursting discs, is located in a pipeline (2,4) and comprises a switching mechanism having two non contacting components one (22) of which is secured in the pipeline, and the other (16) of which is mounted within the pipeline (2,4) remote from the first component (22) to be movable in dependence upon the rate of fluid flow within the pipeline (2,4). When this rate of flow exceeds a predetermined value, the other component (16) of the switching mechanism is moved from a normal rest position to a displaced position to alter the condition of an electric circuit associated with the switching mechanism.

Description

FLUID FLOW DETECTION DEVICE This invention relates to fluid flow detection devices, and has particular, though not exclusive, application to the detection of fluid flow resulting from the rupture of bursting discs and similar pressure-sensitive devices protecting pressurised containers, pipelines and the like.

Bursting discs rupture when the pressure in the associated container exceeds a predetermined maximum value, whereby the container is vented to atmosphere though the ruptured disc.

Such rupture occurs under extreme conditions, and it is desirable that a visual and/or audible indication is given that such conditions exist.

Heretofore it has been relatively conventional practice to provide a U-shaped length of electrically conductive material on a bursting disc so arranged that, when the disc bursts, the conductive material is broken and the condition of an electric circuit associated with the conductive material is altered to actuate a warning mechanism, thereby indicating fluid flow through the disc.

It is necessary for such conductive material to extend from the edge of the disc at least to the centre of the disc, and preferably beyond, and then back to the edge of the disc to ensure effective operation thereof.

Consequently this material is of substantial surface area, and, being relatively fragile, there is a strong susceptibility for non-operational failure i.e. the material breaks other than on rupture of the disc, and therefore gives a false indication of the condition of the associated equipment.

It would be desirable to be able to provide a device capable of detecting a change in the rate of fluid flow that is less prone to damage and more reliable than known arrangements.

According to the present invention there is provided a fluid flow detection device for location in a pipeline, the device comprising a non-contact electric switching mechanism one component of which is secured within the pipeline, and the other component of which is mounted within the pipeline remote from the first component to be movable in dependence upon the rate of fluid flow within the pipeline, the arrangement being such that, when the rate of fluid flow within the pipeline exceeds a predetermined value, the other component of the switching mechanism is moved from a normal rest position to a displaced position whereby the condition of an electric circuit associated with said switching mechanism is altered.

Although such a device has a variety of applications, a preferred application is in the detection of rupture of a bursting disc. More particularly, the device is located immediately downstream of the bursting disc, and, under normal operating conditions, the other component of the switching mechanism remains in its normal rest position. On rupture of the disc, the force of the fluid released thereby causes displacement of the other component from its rest position to a displaced position, and a consequential alteration in the condition of the associated electric circuit.

The device is physically independent of the bursting disc, and, as it incorporates a non-contact electric switching mechanism, it does not require a change in its mechanical integrity to indicate the change in the surrounding conditions.

In a preferred embodiment of the invention, the two components of the non-contact electric switching mechanism comprise a magnetically-operated electric switch, conveniently a reed switch, and a magnet.

The electric switch may be fixedly mounted within the pipeline, with the magnet movably mounted within said pipeline.

Alternatively, the magnet may be fixedly mounted within the pipeline, with the electric switch movably mounted within said pipeline.

Preferably the device includes a flexible carrier member one end of which is fixed relative to the pipeline and at or adjacent the other, free end of which is mounted the movable component of the switching mechanism.

Conveniently the carrier member, in use, extends substantially diametrically of the pipeline, the free end thereof lying closely adjacent, but spaced from, said pipeline.

In a preferred arrangement, the carrier member includes a hinge region therein about which the other, free end portion of the carrier member pivots on the application of a force thereto.

A detection device may be arranged to be used on a number of occasions, in which case the displaced carrier member is returned to its normal position after one use and prior to the next use.

Alternatively a device may be arranged for a single use. In such a situation, the hinge region of the carrier member may be arranged to shear on the application to the carrier member of a force exceeding a predetermined value, in which case retaining means, conveniently a length of wire, extends between the portions of the carrier member to each side of said hinge region to restrain movement of the other, free end portion subsequent to shearing of the hinge region.

The device may comprise a mounting ring, adapted to be clamped between adjacent lengths of the pipeline, the one end of the carrier member being secured to said mounting ring at a first region thereof, and the fixed component of the switching mechanism being secured to said mounting ring, at a second region thereof diametrically opposite said first region.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which: Fig. 1 is a front view of a device according to the invention; Fig. 2 is a side view, partly in vertical section, of the device of Fig. 1 located in a pipeline, and Fig. 3 is detail A of Fig. 2.

Referring to the drawings, the illustrated fluid flow detection device is shown clamped between the flanges of two lengths of pipe 2,4 to determine fluid flow along the associated pipeline in the direction of arrow X.

The device includes a mounting ring indicated generally at 6 and including a pair of annular ring portions 8,10 of an electrically insulating material between which is sandwiched a further annular ring portion 11 of a flexible material which may be metal or plastics.

Integrally formed with the ring portion 11 is a carrier member 12 which extends substantially diametrically of the mounting ring 6 with its free end adjacent to but spaced from the mounting ring 6 at the opposite side of said mounting ring to the other fixed end of the carrier member 12.

The carrier member 12 is of generally thin, platelike form and has a notch 14 formed in, across the width of, the downstream face thereof adjacent its fixed end to define a hinge (best seen in Fig. 3) between the fixed end portion of the carrier member 12 and the free end portion of said member 12.

A magnet 16 is fixedly mounted on the carrier member 12 adjacent its free end, the carrier member 12 and magnet 16 being encased in a protective plastics coating 18.

The fixed end portion and the free end portion of the carrier member 12 to each side of the notch 14 are interconnected by a length of wire 20 for reasons which will become apparent.

An electric, magnetically-operated reed switch 22 is fixedly secured to the mounting ring 6 adjacent the free end of the carrier member 12 to be electrically isolated from the carrier member 12 and located in the bore of the pipeline adjacent the defining interior wall thereof. The switch 22 is encased in a protective sheath and is spaced from the magnet 16 by a distance "d" with the carrier member 12 in its normal rest position shown in the drawings. A two core shielded electric cable 24 supplies the switch 22. The magnet 16 and the reed switch 22 thus form two components of a non-contact electric switching mechanism which can be used to detect fluid flow in the pipeline as detailed below.

The mounting ring 6 and associated components are clamped between the flanges of the pipe lengths 2,4.

The arrangement so far described is such that, with the carrier member 12 in its normal rest position extending diametrically of the pipeline, the magnet 16 is positioned to determine the electrical condition of the reed switch 22, and therefore of an electric circuit associated with said switch. This condition may be, for example, closed circuit.

When fluid flows in the direction of arrow X along the pipeline, the force applied thereby on the upstream surface of the carrier member 12 is such as to cause initial distortion of the flat central regions of the carrier member 12 whereby the free end portion thereof is moved away from its normal rest position, this distortion being accompanied by angular displacement of the free end portion of the carrier member 12 about the hinge defined by the notch 14. It will thus be appreciated that the magnet 16 carried by the member 12 is moved away from the reed switch 22 until it is no longer influential upon the condition of the switch 22.

This may occur, for example, on pivoting movement of the carrier member 12 through a minimum angle of typically 150 as indicated by the dotted lines 26,28 showing the starting plane and the displaced plane respectively of the carrier member 12. At this point, the condition of the electric circuit associated with the switch 22 is altered, for example opened, and an audible and/or visual indication of this altered condition is actuated.

Thus, it will be appreciated that the described device can, for example, be located downstream of a bursting disc in such a manner that, under normal operating conditions on the disc, there is no fluid flow in the pipeline, and the carrier member 12 remains in its normal rest position.

On rupture of the disc, however, fluid flows along the pipeline, and the force thereof applied to the carrier member 12 results in actuation of the switching mechanism as detailed above thereby indicating that burst has occurred.

The initial distortion of the planar condition of the carrier member 12 caused by the impact upon the central region thereof of fluid flowing centrally of the pipeline ensures that, if the carrier member is displaced so violently that it bounces back off the interior wall of the pipeline towards its normal rest position, it cannot return to a position in which the magnet 16 influences the condition of the switch 22.

The described device has the considerable advantages of incorporating a fully enclosed electric circuit electrically isolated from all surrounding equipment and arranged for non-contact actuation by relative movement between the magnet 16 and the switch 22. Thus there is no change in the mechanical integrity of the components of the switching mechanism despite the change in electrical condition of the associated circuit, this change in electrical status being effected by removal of the magnetic field of the magnet 16 from the vicinity of the switch 22.

The described device has a multitude of applications other than to give an indication that a bursting disc has ruptured. It can be used in a broad range of piped fluid systems to indicate a finite change in the rate of fluid flow such as may be required to ensure the overall safety/integrity of the systems and processes with which it is associated.

The device can be constructed on a modular basis which uniquely allows it to be matched with specific operational requirements. It has application in chemically, thermally and mechanically aggressive environments, or any combination thereof, and can be used in conjunction with liquid, vapour, steam, gas or complex mixtures of these.

The described device can be tuned for installation in systems which require the detection of fluid flow rates of a very low or very high magnitude.

The mechanism of the carrier member 12 in particular can be varied to suit required circumstances. The surface area of the free end portion of the carrier member 12 can be altered to increase or decrease the forces applied thereto by a given rate of fluid flow, while the angle of displacement of the carrier member 12 to effect activation of the switching mechanism can be chosen as required, or calibrated to give an indication of specific rates of fluid flow.

The device may be arranged for multiple operation - i.e. the planar condition of the carrier member can be restored and the free end portion of the carrier member 12, subsequent to pivoting movement to a displaced position on the application thereto of a force to be detected, can be returned to its normal rest position.

Alternatively, the device may be arranged to provide for detection of a single event - i.e. once the free end portion of the carrier member 12 pivots beyond a predetermined minimum angle, associated with changing the status of the associated circuit, about the hinge defined by the notch 14, said portion cannot be returned to its normal rest position.

The free end portion of the carrier member 12 may be arranged to pivot through 900 from its rest position under the conditions to be detected to extend substantially axially of the pipeline in its displaced position. The hinge defined by the notch 14 may be located other than as illustrated and may be arranged to shear under the conditions to be detected, the wire 20 preventing the sheared-off portion of the carrier member 12 from flowing along the pipeline and possibly damaging associated equipment.

In single use applications of the device, the switch 22 may be mounted on the downstream face of the free end portion of the carrier member adjacent the free end thereof, and the magnet 16 fixed to the pipeline adjacent the switch 22, the switch moving with the carrier member and being urged into forcible engagement with the pipeline on pivoting movement thereof through 900 whereby the switch is smashed on impact.

Although the non-contact switching mechanism has been described as of a magnetic nature, it may be of, for example, an optical nature in operation.

Other modifications and variations from the described arrangements will be apparent to those skilled in the art, as will be the variety of applications of the device of the invention - the basic concept being to detect a change in rate of fluid flow using a non-contact electric switching mechanism.

Claims

1. A fluid flow detection device for location in a pipeline, the device comprising a non-contact electric switching mechanism one component of which is secured within the pipeline, and the other component of which is mounted within the pipeline remote from the first component to be movable in dependence upon the rate of fluid flow within the pipeline, the arrangement being such that, when the rate of fluid flow within the pipeline exceeds a predetermined value, the other component of the switching mechanism is moved from a normal rest position to a displaced position whereby the condition of an electric circuit associated with said switching mechanism is altered.

2. A device as claimed in claim 1 in which the two components of the non-contact electric switching mechanism comprise a magnetically-operated electric switch and a magnet.

3. A device as claimed in claim 2 in which the electric switch is a reed switch.

4. A device as claimed in claim 2 or claim 3 in which the electric switch is fixedly mounted within the pipeline, with the magnet movably mounted within said pipeline.

5. A device as claimed in claim 2 or claim 3 in which the magnet is fixedly mounted within the pipeline, with the electric switch movably mounted within said pipeline.

6. A device as claimed in any one of claims 1 to 5 and including a flexible carrier member one end of which is fixed relative to the pipeline and at or adjacent the other, free end of which is mounted the movable component of the switching mechanism.

7. A device as claimed in claim 6 in which the carrier member, in use, extends substantially diametrically of the pipeline, the free end thereof lying closely adjacent, but spaced from, said pipeline.

8. A device as claimed in claim 6 or claim 7 in which the carrier member includes a hinge region therein about which the other, free end portion of the carrier member pivots on the application of a force thereto.

9. A device as claimed in claim 8 in which the hinge region of the carrier member is arranged to shear on the application to the carrier member of a force exceeding a predetermined value, retaining means extending between the portions of the carrier member to each side of said hinge region to restrain movement of the other, free end portion subsequent to shearing of the hinge region.

10. A device as claimed in any one of claims 6 to 9 and comprising a mounting ring, adapted to be clamped between adjacent lengths of the pipeline, the one end of the carrier member being secured to said mounting ring at a first region thereof, and the fixed component of the switching mechanism being secured to said mounting ring, at a second region thereof diametrically opposite said first region.

11. A fluid flow detection device substantially as described with reference to and as illustrated by the accompanying drawings.