GB2344154A

GB2344154A - Closure means for flow switch

Info

Publication number: GB2344154A
Application number: GB9928058A
Authority: GB
Inventors: Michael Page; Francis Peter Mcverry
Original assignee: Concentric Controls Ltd
Current assignee: Concentric Controls Ltd
Priority date: 1998-11-26
Filing date: 1999-11-26
Publication date: 2000-05-31
Anticipated expiration: 2019-11-26
Also published as: GB2344154B; GB9825773D0; GB9928058D0

Abstract

A flow switch comprises a flow passage 10 with two or more parts 12, 14 wherein one part 12 is smaller in cross-section than the others, a plug 34 with a seal 38 for stopping the flow passage, means 26 for biasing the plug 34 towards its closed position and further means 46 enabling the plug to close against a flow of fluid allowing greater sensitivity. The enabling means preferably comprises small V or U shaped slots 46 in the seal 38 of the plug. The part 14 against which the plug 34 seals is preferably shallowly tapered and frusto-conical. The seal 38 may be cup-shaped and made of resiliently deformable material. The biasing means 26 is preferably a spring. The plug 34 may contain magnetic material to enable a reed switch exterior of the flow passage to sense its movement and thus detect the rate/commencement of flow of fluid and/or the presence of leaks.

Description

swrrc This invention relates to flow switches which are used to indicate the flow of fluid in a passage, for example the flow of water in pipe.

An object of the invention is to provide a flow switch with good sensitivity. This means a switch capable of giving an indication when the actual flow rate is very small.

According to one aspect of the invention a flow switch comprises a flow passage having fm and second parts of diffemt cross sectional areas, a plug movable between a closed and open position in the first and second parts respectively, the plug having a seal for substantially preventing flow of fluid between the first and second parts when in the closed position, means for biasing the plug towards the closed position and means enabling movement of the plug towards the closed position against the action of a substantially incompressible fluid. The movement enabling means can comprise a fluid passageway through the seal to enable flow of some fluid between the first and second parts as the plug approaches the closed position. For example, the passageway can be a discontinuity or slot in a peripheral seal of the plug.

Preferably, the second part is tapered thereby to enable compression of the seal as the plug approaches the closed position. Preferably, this enables a narrowing of the passageway thereby successively to decrease the amount of fluid which can flow between the first and second parts as the plug approaches the closed position. Preferably the angle of taper is in the order of 1-10 and more preferably in the order of 5 . The second part can be fvsto-conical in shape.

Preferably the passageway comprises a third part adjacent the second part which has a larger cross sectional area than the second part. The third part can also be frusto-conical. A fourth part of the flow passage can also be provided having an even greater cross sectional area than the third part, which fourth part allows full flow of fluid even when the plug is contained in the fourth part.

Preferably, the plug comprises means to enable detection of movement of the plug such as magnetic material or a coil for example.

Preferably, the seal comprises resiliently deformable material. A peripheral slot in the seal can be formed to provide the fluid flow enabling means. Preferably the seal comprises a cup seal. Preferably the slot is V or U shaped. The maximum width of the slot might be in the order of 0.1 to 2 mm and preferably is in the order of 1 mm. Preferably the slot has a cross sectional area of approximately 0.4 rnrn2.

According to another aspect of the invention a flow switch comprises a flow passage having a first part of a first diameter, a second part which is frusto-conical with the smaller end of the frusto-cone of said first diameter and juxtaposed with said first part, the larger end of the frusto-cone opening to a third part which is of larger cross sectional area than said first part, a plug with a peripheral seal located in the flow passage, spring means urging the plug against flow towards the first part, and at least one discontinuity in the peripheral seal arrange so that in use spring driven movement of the plug which takes the seal along the length of the frusto-cone and said seal is progressively deformed by contact with the wall of the second part The invention is more particularly described, by way of example only, with reference to accompanying drawings, in which : Fig 1 is a schematic side elevation view of the such according to the invention in a closed position; Fig 2 is a view of the switch shown in Fig 1 when in a closed position ; Fig 3 is a front elevation view of plug 22 ; Figs 4a and 4b are views of the cup seal according to the invention; Fig 5 is a schematic sectional view of a notched seal according to the invention ; and Figs 6 and 7 are schematic side elevation views of a second embodiment of a switch according to the invention.

The flow passage 10 composes a first part 12 of constant uniform diameter which leads to a second flow passage part 14 which is slightly tapered, that is to say it is a frusto-cone with the smaller end coincident with the passage 12. The larger end of the frusto-cone opens to a larger frusto-cone part 14, which forms the third passage part. This part joins a chamber or fourth part 18.

The angle of taper of second part 14 can be in the order of 5 . Preferably the angle of taper of third part 16 is in the order of 45 . The length L of second part 14 can be in the order of 5 mm.

A fitting 20 at the down stream end of the chamber 18 provides an outlet passage 22 which conveniently is of the same diameter as the passage portion 10. The fitting 20 provides an end abutment 24 for a helically coiled compression spring 26. Fitting 20 comprises a third portion 28 for co-operating engagement with a threaded portion of passage 10 adjacent chamber 18. The fitting 20 comprises a slot for an o-ring seal 30 which abuts the body forming passage 10 thereby to provide a seal. A second outer threaded part 33 of fitting 20 is also provided to enable connection of the flow sensor or flow switch S according to the invention to an existing passageway. The Ieft hand side of sensor S as shown in figure 1 is similarly connectable to existing piping thereby enabling location of switch S in a suitable position.

The movable part of the switch comprises plug 34 which is formed with a peripheral groove 36 receiving a cup seal 38. The plug is unitary with a carrier 40 comprising, in this instance, four segments 42 which may serve to guide the carrier and plug in movement along the axis of the flow passage parts between the closed and open positions as illustrated. The use of a series of segments 42 and in particular the spaces or ports provided by the spaces between them ensures that the cross sectional area open for flow in the chamber 18 is equal to the cross sectional area of the passages 10 and 22, so that in an appropriate position of the plug and carrier (such as the fully opened position illustrated in figure 2) there is no impediment to flow through the switch.

The cup seal 38 is an annular component of somewhat v-shaped cross section at any point around its w and one of the limbs of the vee is notched at one point so as to makc the periphery of the seal discontinuous. The notch 46 shown in figure 4B has a V shaped cross section. The notch is approximately 1 mm wide by 1 mm deep. In another fom the notch can be semi-circular and for example formed by pressing a heated wire against seal 38 which can be formed of suitable plastic material.

The plug is movable when the pressure of the fluid in the passage 10 exceeds the loading provided by the spring 40. Such pressure displaces the plug from the closed position to the open position and that movement of the plug may be detected by an associated electrical device which provides the indication of fluid flow.

For example the plug may carry a magnetic material which can complete a flux path through the wall of the chamber. Alternative possibilities exist for converting the axial movement of the plug into the required indication. The preferred plug 44 comprises a suitable machineable material such as PTFE which can be loaded with magnetic material such as a disc of ferro-magnetic material. The disc can be encapsulated in the PTFE for example.

In use flow sensor S is located in a fluid pipe line in series with a stop valve for preventing fluid flow or other device having known flow characteristics. The displacement of plug 34 can thus be used to monitor the rate of flow of fluid through the flow sensor S and/or to act as a simple switching mechanism to detect commencement of flow. Accordingly, a leak can be detected if for example the stop valve is known to be in a closed position and thus flow should not be occurring. Alternatively, the flow sensor S can be used in combination with a timcr to enable leak detection for example if flow continues above a certain rate for a time greater than a predetermined period.

Flow sensor S operates by plug 34 adopting a closed position when there is no fluid flow. This is achieved using spring 26 which co-operates with carrier 40 and abutment 24 of fitting 20 thereby to push plug 34 and hence seal 38 into the smaller diameter passageway of first part 12. Suitable location of a magnetic sensor such as a reed switch adjacent plug 34 enables detection of axial movement of plug 34 away from passageway 12 into passage 18 and hence the open position shown in figure 2. This open position is effected due to the pressure of fluid in passageway 12 acting on plug 34 to force it through to passage 18. Hence seal 38 expands, due to its natural resilience, as it enters fiusto-conical region 14. Above a certain load or pressure of fluid in the passageway, plug 34 is forced into the open chamber 18 thereby allowing full flow of fluid through outlet 22. When the fluid pressure reduces or stops, spring 26 acts to push plug 34 back towards the closed position shown in figure 1. This movement towards the closed position is assiste by notch 46 which allows a small amount of fluid to pass over plug 34 in spite of the fact that spring 26 is effectively working against an incompressible fluid in first passageway part 12.

It has been found experimentally that the width of the notch is important to the sensitivity of the switch. The smaller the notch, the greater the sensitivity, that is to say the greater the possibility of the plug moving for a given (small) pressure differential. The angle of taper of the portion 12 is also important in relation to the sizc of the notch so that as the pressure begins to overcome the spring and move the plug the seal 38 will permit fluid flow past it after a relatively short axial movement. For example, a taper of 5 in second part 14 and a notch of cross section of approximately 0.4 mu'entables flow rate detection of approximately 0.2 litres per hour.

A further point of importance in the design is in allowing the seal to reestablish against a head of static fluid pressure in that fluid can be displaced by the plug as it travels to the closed position via the notch until the very last small extent receiving movement of the plug, Referring to Figs 6 and 7, there is shown a second embodiment of a switch or close sensor according to the invention wherein switch 110 comprises substantially the same parts as switch 10 shown in Figs 1-5, except that seal 38 is oriented in the opposite direction with respect to the direction of flow of fluid, accordingly, the tapered portion of seal 38 tapers backwardly thereby increasing in outer diameter in the axial direction towards the main body of plug 34. Accordingly, the direction of taper of seal 38 is in the same direction as the frusto-conical sections 14 and 16 of the second and third part of the passageway for fluid flow.

Claims

CLAIM ;- 1. A flow switch comprising a flow passage having first and second parts of different cross sectional areas, a plug movable between a closed and open position in the first and second parts respectively, the plug having a seal for substantially preventing flow of fluid between the first and second parts when in the closed position, means for biasing the plug towards the closed position and means enabling movement of the plug towards the closed position against the action of a substantially incompressible fluid.
2. A flow switch according to claim I wherein the movement enabling means comprises a fluid passageway through the seal to enable flow of some fluid between the first and second parts as the plug approaches the closed position.
3. A flow switch according to claim 2 wherein the passageway comprises a discontinuity around the scaling interface of seal of the plug.
4. A flow switch according to claim 1,2 or 3 wherein the second part is tapered thereby to enable compression of the seal as the plug approaches the closed position.
5. A flow switch according to claim 4 wherein the second part enables a narrowing of the passageway thereby successively to decrease the amount of fluid which can flow between the first and second parts as the plug approaches the closed position.
6. A flow switch according to claims 4 or 5 wherein the angle of taper is in the order of 1-10 and more preferably in the order of 5 .
7. A flow switch according to claims 4,5 or 6 wherein the second part is irusto-conical in shape.
8. A flow switch according to any preceding claim wherein the passageway comprises a third part adjacent the second part which has a larger cross sectional area than the second part,
9. A flow switch according to claim 8 wherein the third part is frusto-conical.
10. A flow switch according to claims 8 or 9 wherein comprising a fourth part of the flow passage provided having a greater cross sectional area than the third part.
11. A flow switch according to claim 10 wherein the fourth part allows full flow of fluid even when the plug is contained in the fourth part.
12. A flow switch according tG any preceding claim wherein the plug comprises means to enable detection of movement of the plug such as magnetic material or a coil for example.
13. A flow switch according to any preceding claim wherein the seal comprises resiliently deformable material.
14. A flow switch according to any preceding claim wherein the seal comprises a peripheral slot to provide the fluid flow enabling means.
15. A flow switch according to claim 14 wherein the slot is V or U shaped.
16. A flow switch according to claims 14 or 15 wherein the width of the slot is in the order of 0.1 to 2mm and preferably is in the order of 1mm.
17. A flow switch according to claims 14, 15 or 16 wherein the slot has a cross sectional area of approximately 0.4mm2.
18. A flow switch according to any preceding claims wherein the seal comprises a cup seal.
19. A flow switch comprising a flow passage having a first part of a first diameter, a second part which is frusto-conical with the smaller end of the Susto-cone of said first diameter and juxtaposed with said first part, the larger end of the fiusto-cone opening to a third part which is of larger cross sectional area than said first part, a plug with a peripheral seal located in the flow passage, spring means urging the plug against flow towards the first part, and at Ieast one discontinuity in the peripheral seal arranged so that in use spring driven movement of the plug which takes the seal along the length of the frusto-cone and said seal is progressively deformed by contact with the wall of the second part.
20. A seal for a flow switch comprising a sealing interface having a discontinuity.
21. A seal according to claim 20 wherein the discontinuity comprises a slot.
22. A seal according to claim 21 wherein the slot is V or U shaped.
23. A seal according to claims 21 or 22 wherein the width of the slot is in the order of 0. 1 to 2mm and preferably is in the order of lmm.
24. A seal according to claims 21,22 or 23 wherein the slot has a cross sectional area of approximately 0.4rnm2.
25. A seal according to any of claims 21 to 24 comprising a cup seal.