WO1993001606A1

WO1993001606A1 - Fluid flow sensing switch

Info

Publication number: WO1993001606A1
Application number: PCT/AU1992/000321
Authority: WO
Inventors: Kerry James Field
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-07-05
Filing date: 1992-06-30
Publication date: 1993-01-21
Anticipated expiration: 1994-01-05

Abstract

A corrosion resistant fluid flow switch for insertion in a fluid flow channel or line. The flow switch comprises a housing, at least one switch assembly connected to a power source and located therein, a paddle arm (6) electrically and mechanically isolated from the switch and pivotally attached within or to said housing thereby forming two free ends with one of said ends engaging with the fluid in which the fluid flow switch is at least partially inserted. The other end has at least one magnet (7) embedded in the paddle arm which, in conjunction with at least one other opposing biasing magnet (21) located within or on the housing, biases according to the polarity of the magnets the paddle arm (6) towards a natural repose position wherein the switch assembly is either open or closed according to a predetermined configuration of the switch assembly and paddle arm, wherein, when fluid flows in one direction resisting the bias, the switch assembly adopts either an open or closed condition commensurate with the predetermined configuration and when fluid flow in that direction stops or flows in the opposite direction, the paddle arm (6) returns to its position of natural repose thereby closing or opening the switch assembly.

Description

FLUID FLOW SENSING SWITCH

This invention relates to improvements in fluid flow sensing switches. More particularly, the invention relates to a fluid flow switch comprising an actuating paddle arm which is corrosion resistant and operable by a magnet or magnets encased in the paddle arm acting in conjunction with a switch.

Devices for switching on and off electrical circuits, and remotely controlling electrical equipment, when fluid either flows, or ceases to flow in a pipe or conduit, or open channel, are collectively known as flow switches. These switches according to the prior art usually comprise a housing, a switch assembly and a paddle of sheet metal or plastic positioned so fluid flow impinges on the paddle face and causes it to deflect. A switch which may be mechanically or magnetically actuated is controlled by the deflection of the paddle, and thus a switch output is obtained.

The paddle deflection which is responsive to fluid flow usually occurs against a spring bias, or counter weight, so that when flow ceases the paddle returns to its undeflected state or state of natural repose under the action of the spring bias or weight. In order to adjust the sensitivity of flow switches an external method of pre-loading the spring is employed. This usually consists of an adjusting screw with suitable sealing, positioned to compress the pre-load spring. Where corrosive or aggresive fluids are to be sensed, conventional paddle flow switches tend to be unsuitable, due to corrosion of the metal components and potential leakage of fluids through spring seals, bellows or adjusting screws.

One example of a prior art flow switch involves the use of magnets attached to the top end of a paddle arm such that the magnet actuates a reed switch. Previously, the types of magnets which has been used comprised aluminium, nickle and cobalt. The prior art flow switches have adopted the use of a metal bellows to which the top end of the paddle arm is attached. The bellows rocks when the arm is moved and trips a micro switch included in a flow switch housing. A sensitivity adjustment is provided in this type of flow switch by means of a spring loaded screw in the housing which retards the rocking of the bellows and provides a sensitivity adjustment. One problem that exists with the bellows type flow switches is that the sensitivity of the switch is directly related to the mechanical strength of the bellows. As the bellows wears out, the sensitivity of the switch decreases thereby reducing its efficiency and effectiveness. If the bellows is made from very thin metal the switch can have a high degree of sensitivity but a very low pressure rating. On the other hand, if the bellows is strong, the switch is less sensitive but has a high pressure rating. As an example of this the typical switch may be rated at 10 bars but will be irreversibly damaged by fluid pressures over 20 bars.

The prior art switches have generally been made of metal, for instance, the flow switch may have a bronze body and stainless steel paddle arm. The flow switches have also adopted conventional micro switches or reed switches.

One of the major disadvantages of the prior art flow switches is their inability to resist the effects of corrosion. The bellows type switches suffer from the insensitivity problems referred to earlier and in addition suffer from the effects of corrosion when the air bubble which initially protects the mechanical switching mechanisms when the flow switch is placed in situ, degrade and allow the fluid in which the paddle arm sits to contact the operating mechanisms thereby leading to corrosion of the mechanisms and in the case of switches which utilise magnets, corrosion of the magnets. This dramatically reduces the efficiency of the switch and ultimately results in a necessity for replacement.

The present invention seeks to overcome the prior art disadvantages by providing a flow switch wherein the paddle arm is made of a plastics material and carries within the paddle a magnet isolated from contact with the fluid in which the paddle is located. This type of switch avoids the disadvantages associated with corrosion of mechanical components and resultant insensitivity. The present invention provides finer control of the switching threshold compared to the spring bias switches, zero friction associated with the adjusting mechanism across the entire adjustment range, elimination of spring fatigue or corrosion and an elimination of change in switch sensitivity over the life of the switch as well as a higher pressure rating.

In its broadest form the present invention comprises; a corrosion resistant fluid flow switch for insertion in a fluid flow channel or line, said flow switch comprising; a housing, at least one switch assembly connected to a power source and located therein, a paddle arm electrically and mechanically isolated from the switch and pivotally attached within or to said housing thereby forming two free ends, one of said ends engaging with the fluid in which the fluid flow switch is inserted; and at the other end at least one magnet embedded in the paddle arm which, in conjunction with at least one other opposing biasing magnet located within or on the housing, biases the paddle towards a natural repose position wherein the switch assembly is either open or closed according to the predetermined configuration of the switch assembly and the paddle arm; wherein, when fluid flows in one direction resisting the bias, the switch assembly adopts either an open or closed condition commensurate with said predetermined configuration and when fluid flow in that direction stops or flows in the opposite direction, the paddle arm returns to its position of natural repose thereby closing or opening the switch assembly.

In another broad form the invention comprises: a corrosion resistant fluid flow switch for insertion in a fluid flow channel or line; said flow switch comprising; a housing, at least one switch assembly located within the housing and connected between a power source and an appliance, a paddle arm electrically and mechanically isolated from the switch and pivotally attached within or to said housing thereby forming two free ends with one of said ends engaging with the fluid in which the fluid flow switch is inserted and at the other end at least one magnet embedded in the paddle arm which, in conjunction with first and second biasing magnets, the first located on the housing and the second magnet spaced apart from the first magnet and located on a biased switching arm bias the paddle towards a natural repose position wherein the switch assembly is either open or closed according to the predetermined configuration of the switch assembly and paddle arm; wherein, when fluid flows in one direction resisting the bias, the switch assembly adopts either an open or closed condition commensurate with said predetermined configuration and when fluid flow in that direction stops or flows in the opposite direction, the paddle arm returns to its position of natural repose thereby closing or opening the switch assembly.

In a preferred embodiment the fluid flow switch comprises in the housing one or more biasing magnets which is/are adjustable relative to the magnet or magnets in the paddle arm so as to alter switch sensitivity according to requirements. According to the preferred embodiment the housing is substantially T shaped with the outstanding leg of the T comprising a hollow cavity into which the paddle arm locates. The paddle arm has an integral pivot which locates in recesses in the housing from within the housing cavity. The magnets used in the paddle arm and housing may comprise Neodymium, Iron, Boron increasing magnetic power to simulate spring strength operation.

The paddle arm is electrically and mechanically isolated from the flow switch, and also from the biasing magnet. This prevents fluid within which the fluid flow switch is located coming in contact with any metallic part which could be susceptacle to corrosion.

The present invention will now be described in more detail according to a preferred but non limiting embodiment and with reference to the accompanying illustrations wherein: Figure 1: presents a long sectional view of the flow switch according to a preferred embodiment of the invention. Figure 2: represents a side elevational view of the flow switch according to the embodiment of figure 1. Figure 3: represents a sectioned side elevation of the flow switch of the embodiment of figure 1. Figure 4: represents a partly disassembled version of the preferred embodiment of figure 1 showing the bearing screw released. Figure 5: shows an alternative embodiment of the invention.

Referring to figure 1 there is shown a sectional view of a flow switch 1 according to a preferred embodiment of the invention. Flow switch 1 comprises a body 2 which is preferrably injection molded from a chemically inert thermo plastic material such as polypropolene. Housing 2 is formed substantially in the shape of a T comprising two principle sections, a main housing 3 and a connecting leg 4. Connecting leg 4 comprises a cavity 5 within which paddle arm 6 fits. The paddle arm comprises a substantially elongated member having one end adapted to engage with the fluid in which the fluid flow switch is to be used and the other end comprising at least one magnet. End 8 of the paddle arm 6 comprises a substantially planar paddle member 9 which presents a face to the direction of fluid flow and which enables the paddle arm to pivot about bearing pin 10. Preferrably, bearing pin 10 is molded as an integral part of the paddle arm 6. Preferably, the paddle arm is injection molded from a suitable chemically resistant and resilient thermo plastic such as polycarbonate. The bearing pin 10 is held in position by means of eccentric bearing screw 11. The bearing screw 11 is screwed into connecting leg 4 of the body 1. Bearing screw 11 is sealed by an 0-ring 12 which nests in a recess (not shown) in the body of the connecting leg 4. Bearing pin 10 locates in recess 13 in connecting leg 4. When the paddle arm 6 is screwed into position by means of bearing screw 11 the paddle arm is free to pivot within the confines of cavity 5 about the axis of bearing pin 10. It is important that there be no additional play in the paddle arm other than the allowable rotation about the axis of the bearing pin 10. Magnet 7 of paddle arm 6 is embedded in the material of the paddle such that it is totally covered by the plastics material. Thus, there is no metallic contact between air and/or fluid in which the flow switch is placed. Magnets may be cylindrical or a planar disc as shown or alternatively, they may be a number of different shapes and comprise Neodymium, Iron and Boron. As an alternative to molding in of the magnet it is possible to insert the magnet/s in the body of the paddle and then place a cover over the magnet opening. Housing 3 comprises therein a circuit board assembly 14 with screw means 15 anchoring the circuit board to the base 16 of the housing 3. Associated with the circuitry is a reed switch 17 which is outstanding from the circuit board so that it presents in the direction of the magnetised upper end of the paddle arm. Figure 2 shows an external side view of the flow switch depicted in figure 1. Connecting leg 4 is adapted with threaded shank 18 to facilitate connection with a fluid flow pipe not shown.

Referring to figure 3 there is shown a sectional view of the flow switch of figures 1 and 2 rotated through 90 degrees. Connecting leg 4 also has a part 19 which is threaded internally and forms a blind bore which terminates in the body of the connecting leg 4 before it would otherwise enters cavity 5. Within the port 19 is an adjusting screw 20 which is fitted with a magnet 21 at the extremity of shank 22. Magnet 21 is orientated so that its pole face matches the pole face of magnet 7 which is molded into the paddle arm 6. According to one embodiment the polarity of the respective magnets 21 and 7 are such that magnet 21 tends to repel magnet 7 away from it such that the natural repose position of the paddle arm 6 is rotated away from magnet 21 to the limits of its travel by the interaction of the two magnets. In an alternative embodiment and with reverse polarity of the magnets 21 and 7, a natural repose position of the paddle arm 6 can be as shown in figure 3. According to this methodology the paddle arm 6 can be preloaded away or preloaded toward the adjusting magnet 21 by effecting an appropriate adjustment to the polarity. For convenience, the screw 22 is provided with a screw driver slot 23 so as to enable the adjustable biasing of magnet 21 and movement thereof inward or outward relative to the position of magnet 7 in the paddle arm 6 in order to increase or decrease the magnetic preload on the paddle arm 6 .

This adjustment capability provides a range of sensitivities for the reed switch 17. The use of this methodology achieves what the mechanical action achieved in the prior art devices effected by an adjustable spring sensitivity mechanism but with an elimination of the disadvantages of the spring and without any mechanical intrusion into the wet cavity of the flow switch. By a combination of the magnetic repulsion, paddle preload and the integral thermo plastic pivot bearings, the flow switch may be produced in which there are no metal components exposed to the fluid being sensed. This represents an advantage over the conventional metal or metal/plastic flow switches.

The flow switch 1 described uses a magnetically coupled reed switch 17 to achieve an electric output. Magnet 7 in the paddle arm 6 has sufficient pole strength to actuate reed switch 17. The reed switch 17 may be used directly as the electrical output device or it may be used to gate into conduction a solid state switch such as a triac, to control a relay. As shown in figures 1 to 4 the housing 3 is sealed against connecting leg 4 by means of sealing rings 24. Housing 3 houses the circuit board 14 which acts as the reed switch 17 and also a cable termination block 25. Cable termination block 25 enables connection of an electrical appliance to the switch which is to be actuated according to the operation of the flow switch depending upon how it is set relative to fluid flow.

In a preferred embodiment a heat sink 26 is optionally included in the housing to support a triac 27. Housing 3 is positioned by means of screws 15. Beneath the heads of the screws 15 are 0 ring seals 28. A cable gland 29 is shown screwed to the housing 3. When the housing 3 is constructed and anchored in this way, the electrics inside are rendered waterproof and electrically safe.

In use, the flow switch body 1 is connected by a threaded portion 18 into a T in a pipe line. Paddle arm 6 would normally be cut or profiled so that when the flow switch was installed in the pipe system, the paddle 9 protrudes into the flow stream but does not contact any part of the pipe including the pipe walls. Prior to setting of the flow switch into position in a fluid flow line an operator first must decide on the directional polarity of the magnets so as to decide on the repose position of the paddle arm 6. Which ever biasing arrangement is decided, that is, whether the magnets are repelling or attracting, the flow switch is inserted such that the fluid flow in order to actuate the paddle arm 6 passes in a direction which tends to resist the biasing forces exerted by the magnets. When fluid flow impinges on the paddle 9 paddle arm 6 deflects and rotates about the axis of pivot 10. When the magnet 7 is moved such the influence of the magnetic field impinges on the reed switch 17, the switch is turned to the on position. At the same time and according to the embodiment shown in figure 3, a strong attraction exists between the magnets 21 and 7 due to their close proximity. The fluid flow has the tendancy to resist this attracting bias moving the magnets away from each other and magnet 7 closer to the reed switch 17. When flow ceases, the magnet is attracted back to its position of natural repose of attraction between magnets 21 and 7. In the alternative embodiment and where there is reverse polarity, magnets 21 and 7 are repelled such that the natural repose position of the paddle arm 6 is such that the magnets are at maximum separation. According to this embodiment, when fluid flows, the tendancy is for the magnets 21 and 7 to be forced towards each other against the action of the repulsive bias. In this embodiment, when flow ceases or is reduced to a very low rate, the repulsion between the magnets 21 and 7 causes the paddle arm 6 to again be pushed away and out of proximity of the reed switch 17 thereby causing the reed switch to revert to the off condition.

Various alternative arrangements of the magnetic isolating adjusting system are available and clearly apparent from the described embodiment. The magnets 21 and 7 for instance, may be arranged to attract or repeal each other depending on the orientation of the magnetic poles and the nature of the switch requirements according to the fluid flow required. The position shape and numbers of magnets may be varied in the paddle arm and housing. The effective action of the magnets simulates the mechanical action of the prior art devices by simulating a biasing effect. The adjusting biasing magnet 21 may be replaced by a piece of ferrous material such as iron and provided magnet 7 has sufficient strength, it will be attracted to the metal. The net effect of this is an arrangement which performs the same function as that achieved in the use of a tension spring arrangement.

As with the magnets, the electrical function of the flow switch may be reversed to provide an on condition when there is no flow acting against the paddle arm 6 and an off condition when flow impinges on the arm 6. This reverse function is achieved by turning the entire electrical board assembly around and due to the reed switch 17 being positioned out of centre with respect to the paddle arm 6 and out of center of opposite hand effect is achieved which reverses the output of the switch.

Referring to figure 4 there is shown a sectional view of a flow switch according to the preferred embodiment of figure 1 this time showing bearing pin 11 released. Paddle arm 6 is displaced sideways to a point where the bearing pin 11 on the side of the paddle arm has disengaged from bearing hole 30. In this position the paddle arm may be removed without withdrawing it axially. As can be seen from figure 4, a trench 31 is provided within the body of connecting leg 4 to allow the off side bearing boss to clear the body cavity and thus be withdrawn or reassembled. The paddle arm depicted in figures 1 to 4 is intended for use in applications which require the flow switch to be fitted into pipes in which liquids may be flowing. It is nevertheless possible for the flow switch to be utilised for indicating flow conditions of other fluids such as gases. Furthermore, it is practical to employ the flow switch to monitor liquid flow in open channels to detect flows of vapours. Referring to figure 5 there is shown a flow switch according to an alternative embodiment wherein there are three magnets used.

Figure 5 depicts a flow switch actuated by a paddle arm 32, as previously described, to which a micro switch 33 is fitted. The micro switch 33 is fixed to a backing plate 34 which is held in position against the flow switch body 35 by the two fixing studs 36. The micro switch 33 is provided with an arm 37, of preferably non ferrous material, such as brass or stainless steel. The arm 37 is free to pivot about a bearing pin 38. Close to the free end of the arm 37, a magnet 39 is suitably fixed. This magnet is oriented so its face pole repels against the paddle magnet 40, when the paddle arm 32 is in close proximity thereto.

A small compression spring 41 is provided to balance the weight of the arm 37 and magnet 39, and to act as a mechanical dampener to unwanted movement of the arm 37. The repulsive force developed between the magnets 40 and 39 when in close proximity is sufficient to cause the arm 37 to be lifted, depressing the micro switch button 43. This action causes the micro switch to change electrical state. That is, a closed circuit may be obtained between the micro switch electrical terminals, 44 normally open, and 45 common. An open circuit is obtained between terminals 45 common, and 46 normally closed.

With a correctly installed flow switch, in operation, cessation of flow allows the repulsive magnetic force between the magnets 40 and 42 to cause the top end of the paddle arm 32 to be pushed in a clockwise direction away from the magnet 42. Additionally the movement of the arm 32 relaxes the repulsion between magnets 40 and 39. The free end of the micro switch arm 37 moves slightly downward, releasing the pressure on button 43 and allowing the micro switch to reverse its electrical state. The micro switch is of a single pole double throw type, and a normally on and normally off circuit may be obtained by the provision of common, normally open and normally closed terminals on the micro switch. These are depicted as NO, C, NC, in Figure 5 and on the micro switch.

It is entirely practical to employ other types of micro switches in the previously described method. For example micro switches which are arranged to operate two circuits simultaneously. In addition to electrical micro switches, pneumatic pilot valves may be actuated by the flow switch. Magnetic repulsion may be utilised, in a like manner to the method previously described for electrical switches.

It will be recognised by the persons skilled in the art that numerous variations and modifications can be made to the invention as broadly described herein including but not limiting to altering the shape and configuration of the paddle arm to achieve an increase or decrease in sensitivity relative to the density and/or velocity of the fluid being monitored, altering the size and length of the paddle arm, adjusting the polarity of the magnets and but not limited to reversing the action of the switch, and changing the numbers of magnets used in the paddle arm and/or housing without departing from the overall spirit and scope of the invention as broadly described herein.

Claims

CLAIMS: 1. A corrosion resistant fluid flow switch for insertion in a fluid flow channel or line, said flow switch comprising; a housing, at least one switch assembly connected to a power source and located therein, a paddle arm electrically and mechanically isolated from the switch and pivotally attached within or to said housing thereby forming two free ends with one of said ends engaging with the fluid in which the fluid flow switch is at least partially inserted; and the other end having at least one magnet embedded in the paddle arm which, in conjunction with at least one other opposing biasing magnet located within or on the housing, biases according to the polarity of the magnets the paddle arm towards a natural repose position wherein the switch assembly is either open or closed according to a predetermined configuration of the switch assembly and paddle arm, wherein, when fluid flows in one direction resisting the bias, the switch assembly adopts either an open or closed condition commensurate with said predetermined configuration and when fluid flow in that direction stops or flows in the opposite direction, the paddle arm returns to its position of natural repose thereby closing or opening the switch assembly.

2. A fluid flow switch according to claim 1 wherein the biasing magnet/s is/are adjustable relative to the magnet/s in the paddle to enable adjustment of the degree of biasing force created by said magnets thereby adjusting switch sensitivity.

3. A fluid flow switch according to claim 2 wherein part of the paddle is located within the housing in a wet cavity which is in communication with the fluid; and wherein the paddle is not in direct electric or mechanical contact with either the switch or the said at least one biasing magnet/s.

4. A fluid flow switch according to claim 3 wherein magnetic forces from the magnet/s in the paddle arm operate the switch when the magnet/s move to a location which influences the switch.

5. A fluid flow switch according to claim 4 wherein the pivot for the paddle arm is moulded integrally therewith. the pivot locating in recesses within the cavity of the housing.

6. A fluid flow switch according to claim 5 wherein the switch assembly comprises two reed switches operable by the magnet/s such that the first reed switch is closed when the second reed switch is open or the first reed switch is open when the second reed switch is closed according to whether the paddle arm is in its natural position of repose or in a position away from its natural repose.

7. A fluid flow switch according to claim 6 wherein the body of the housing is substantially T shaped with the vertical leg of the T being threaded to facilitate fixation to pipework or to a structure through which or near which fluid flows.

8. A fluid flow switch according to claim 7 wherein the housing and paddle are made from the same plastics material.

9. A fluid flow switch according to claim 8 wherein the paddle arm is, planar, rectangular, triangular or cylindrical along at least a part of its length.

10. A fluid flow switch according to claim 9 wherein the flow switch is mounted either vertically or horizontally to said pipework or structure.

11. A fluid flow switch according to claim 10 wherein the flow switch is rated to withstand pressures up to and greater than 70 bars.

12. A fluid flow switch according to claim 11 wherein the fluid is a liquid.

13. A fluid flo switch according to claim 12 wherein the plastics material is a chemically inert thermoplastic material.

14. A fluid flow switch according to claim 13 wherein the housing and paddle arm are made of polypropolene.

15. A fluid flow switch according to claim 13 wherein the paddle is made of an injection moulded polycarbonate.

16. A fluid flow switch according to claim 15 wherein the housing comprises therein relay circuitry on a circuit board electrically linking the switch to a power source and an electrical apparatus.

17. A fluid flow switch according to claim 16 wherein each of said reed switch/es is/are outstanding from the circuit board so that it/they comes into the influence of the magnetic field of the magnet/s in the paddle arm.

18. A fluid flow switch according to claim 17 wherein one of the adjustable biasing magnets is adjusted by turning a threaded screw to which the biasing magnet is indirectly or directly attached to thereby alter the biasing force.

19. A fluid flow switch according to claim 18 wherein the paddle arm pivot is located in position by means of a bearing screw.

20. A corrosion resistant fluid flow switch for insertion in a fluid flow channel or line; said flow switch comprising; a housing, at least one switch assembly located within the housing and connected between a power source and an appliance, a paddle arm electrically and mechanically isolated from the switch and pivotally attached within or to said housing thereby forming two free ends with one of said ends engaging with the fluid in which the fluid flow switch is at least partially inserted and at the other end at least one magnet embedded in the paddle arm which, in conjunction with first and second biasing magnets, the first located on the housing and the second magnet spaced apart from the first magnet and located on a biased switching arm, bias the paddle towards a natural repose position wherein the switch assembly is either open or closed according to the predetermined configuration of the switch assembly and paddle arm, wherein, when fluid flows in one direction resisting the bias, the switch assembly adopts either an open or closed condition commensurate with said predetermined configuration and when fluid flow in that direction stops or flows in the opposite direction, the paddle arm returns to its position of natural repose thereby closing or opening the switch assembly.

21. A fluid flow switch according to claim 20 wherein one or both of the first and second magnets are adjustable to enable adjustment of the degree of biasing force created by said first and second magnets on the magnet/s in the paddle arm thereby adjusting switch sensitivity.

22. A fluid flow switch according to claim 21 wherein the second magnet is adjustable along the length of the switching arm in order to adjust switch sensitivity.

23. A fluid flow switch according to claim 22 wherein part of the paddle is located within the housing in a wet cavity which is in communication with the fluid; and wherein the paddle is not in direct electric or mechanical contact with either the switch or the said biasing magnet/s.

24. A fluid flow switch according to claim 23 wherein magnetic forces from the magnet/s in the paddle arm operate the switch when the magnet/s move to a location which influences the switch.

25. A fluid flow switch according to claim 24 wherein the pivot for the paddle arm is moulded integrally with the paddle, the pivot locating in recesses within the cavity of the housing.

26. A fluid flow switch according to claim 25 wherein the body of the housing is substantially T shaped with the vertical leg of the T being threaded to facilitate fixation to pipework or to a structure through which or near which fluid flows.

27. A fluid flow switch according to claim 26 wherein the housing and the paddle arm are made of a plastics material.

28. A fluid flow switch according to claim 27 wherein the housing and paddle are made from the same material.

29. A fluid flow switch according to claim 28 wherein the paddle arm is a chemically inert thermoplastic material.

30. A fluid flow switch according to claim 28 wherein the housing and paddle arm are made of polypropolene.

31. A fluid flow switch according to claim 30 wherein the flow switch is mounted either vertically or horizontally to said pipework or structure.

32. A fluid flow switch according to claim 31 wherein the flow switch is rated to withstand pressures up to and greater than 70 bars.

33. A fluid flow switch according to claim 32 wherein the fluid is a liquid.

34. A fluid flow switch according to claim 33 wherein the paddle is made of an injection moulded polycarbonate.

35. A fluid flow switch according to claim 34 wherein the housing comprises therein relay circuitry on a circuit board electrically linking the switch to a power source and an electrical apparatus.

36. A fluid flow switch according to claim 35 wherein one of adjustable biasing magnets is adjusted by turning a threaded screw to which the biasing magnet is indirectly or directly attached to thereby alter the biasing force.

37. A fluid flow switch according to claim 36 wherein the paddle arm pivot is located in position by means of a bearing screw.

38. A fluid flow switch according to claim 37 wherein the paddle arm is, planar, rectangular, triangular or cylindrical along at least a part of its length.

39. A fluid flow switch according to any one of the foregoing claims wherein the permanent magnets are composed of the elements Neodymium, Iron and Boron.