GB2087570A - Fluid flow sensors - Google Patents

Abstract

A fluid flow sensor comprises a flange 1 defining an orifice 3, a flap 11 mounted on a shaft 13 and means for connecting or associating the flap with a fluid flow alarm or indicating device, wherein the flap has a smaller surface area than that of the orifice and is biassed towards its rest position magnetically. Flow in either direction can be sensed. The alarm or indicating device may include a microswitch or inductive proximity switch. <IMAGE>

Description

SPECIFICATION Fluid flow or level sensitive devices This invention concerns fluid flow or fluid level sensitive devices, particularly to such devices arranged to give an alarm or indication when a flow of liquid through a conduit system ceases or commences, or falls or rises to a predetermined level, and incorporating a flap arranged to be displaced by fluid flow and operatively connected to an alarm, control or indicating device.

Such a device is known from British Patent Specification No. 1 303891, in which device the flap is mounted on a shaft rotatably mounted in bearings in a flange member defining a circular flow orifice, the shaft being offset with respect to a diameter of the orifice and the flap in its rest position extending across the flow orifice and engaging a seating or sealing face at part of its periphery. To enable the flap to pivot and rotate the shaft in response to fluid flow through the orifice the flap is formed of a plurality of separate parts hinged together so that the flap can partially fold or collapse as it moves off the seating.The flap is formed of two metal side wings hinged at right angles to the axis of the shaft, to the side edges of a metal central portion, and a restoring spring extending between the two wings across the central portion of the flap ensures that the wings resume a position in which they are coplanar with the central portion as the flap moves to its rest position on the seating but allows the wings to fold as the flap moves away from such reset position. The flap is biassed towards its rest position by means of a counter balance weight-fixed on the shaft. The counter balance weight may be an arm which also affords a visual indication of the flap position.One end of the shaft rotates in a bearing in a blind bore in the inner wall of the flow orifice and the opposite end of the shaft extends through a bearing and seal unit in a bore through the flange to cooperate with a switch mechanism mounted outside the flange.

Problems can arise with such devices due to wear of the bearing at the inner end of the shaft and due to a tendency for the side wings to impede free movement of the flap by frictional engagement with the wall of the orifice.

In order to eliminate or alleviate these problems it was proposed in British Patent Specification No.

1518790 to extend the blind bore so that it became a through bore and to mount the bearing in such bore in such a manner that it could be removed and replaced from the outside of the device without having to dismantle the device from the system in which it was located.

It was further proposed to overcome the problem of the side wings impeding free movement of the flap by coating the wall surfaces of the orifice, at least where engaged by the wings, and/or the wings themselves with a low friction coating, such as PTFE.

However, these proposals have not been entirely successful in eliminating problems associated with such fluid flow or fluid level sensitive devices, particularly relating to friction between the flap and the orifice wall and sticking of the flap in an open position.

Furthermore, having a three part flap is not entirely satisfactory from a manufacturing or operational point of view.

An object of this invention is to provide fluid flow or fluid level sensitive devices wherein the above problems are reduced or eliminated.

According to one aspect this invention provides a fluid flow or fluid level sensitive device comprising a part adapted to define a fluid flow orifice and having a flap-valve-like member positioned in said orifice and movable in accordance with fluid flow therethrough, and means for connecting or associating said member with a fluid flow or fluid level alarm or indicating device, wherein said flap-valve-like member has a smaller surface area than that of the orifice.

The afore-described known devices are only really suitable for monitoring fluid flow in one direction, the flap-valve-like member only being movable through 900. However, in the device of this invention the flap, mainly by virtue of its smaller size, can move through 1800 and so monitor fluid flow in both directions through the orifice.

Since all that is required is an indication of fluid flow or level, the flap does not need to fill the orifice completely to fulfill its purpose. The flap member may have a part of its free end angled out of line with the orifice. Normally the flap member will be associated with means biassing it into its rest position i.e. into the same plane as the orifice.

According to another aspect of the invention there is provided a fluid flow or fluid level sensitive device comprising a part adapted to define a fluid flow orifice and having a flap-valve-like member positioned in said orifice and movable in accordance with fluid flow therethrough, and means associating said member with a fluid flow or fluid level alarm or indicating device, wherein said flap member is biassed towards its reset position magnetically.

Conveniently the orifice is defined by a flange and the flap will usually be mounted on a shaft which passes through a cross bore at right angles to and at one side of the centre of the orifice. One end of the shaft may then be associated with the magnetic means for biassing the flap towards its rest position.

In a preferred embodiment, the shaft has fixed thereon a pair of magnets offset relative to each other and which are between a pair of fixed magnets. Thus one fixed magnet will have its south pole facing the north poles of the shaft magnets and the other its north pole facing the south poles of the shaft magnets. The positioning of the magnets will be arranged so that their reactions will tend to return the flap to its rest position.

Preferably to give a signal indication of the position of the flap, the shaft has a cam associated with it adapted to open or close contacts of a microswitch in accordance with the position of the flap, the microswitch being connected to an alarm or indicator which may show either that fluid is flowing through the apparatus or that fluid flow has stopped. Usually the microswitch will be activated when the flap is in its rest position so as to indicate an alarm state, i.e. when fluid flow has stopped.

In devices where the flap is of smaller surface area than that of the orifice, the resultant freeing of the flap allows a greater number of flap movements. This greater number of flap movements causes a corresponding increase in the number of operations of the microswitch which as a result has a shorter life expectancy. For example a microswitch in a fluid flow alarm device may have to be replaced every two or three voyages.

Thus it is preferred that an alarm state position of the flap activates an alarm or indicator without physical contact between the shaft or a body on the shaft and a switch for opening or closing the alarm or indicator circuit.

This may be achieved by a so-called proximity switch, for example an inductive type, wherein an electromagnetic field is generated by the switch and can be disturbed or affected by the movement or presence of a body in the field. Such a body may be of mild steel.

In a preferred embodiment, the body may be a mild steel body on the shaft which when the flap should indicate an alarm state, e.g. no flow of liquid, is in a position to disturb the electromagnetic field generated by the switch.

This disturbance causes the switch to open or close an alarm or indicator circuit.

Any suitable alarm or indicating device may be associated with the devices of the invention so that either fluid flow or fluid level can be monitored. One particular use of the device of the invention is as a piston coolant flow alarm so as to indicate harmful stoppage of the coolant flow.

This invention will now be further described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a plan view of a first embodiment of a fluid flow sensitive device; Figure 2 is a front view of the device of Figure 1 showing switchbox detail; Figure 3 is a section of part of the device of Figures 1 and 2 taken at right angles to Figure 2.

Figure 4 shows an alternative switchbox arrangement; and Figure 5 is a section along line AA of Figure 4.

Referring to Figures 1 to 3 the device comprises a single flange or thin ring 1 having circumferentially spaced holes 2 by which it is bolted between flanges of two aligned pipes so as to be in the path of flow of fluid through said pipes.

Positioned in orifice 3 is a flap-like member 11 hingedly supported in and by the flange 1 on a shaft 13 to which the flap is fixed by means of screws or the like 12. The flap 11 is generally rectangular and of smaller surface area than the orifice so as to prevent striking thereof due to friction. As shown, the flap has its free end angled relative to the flange.

The shaft 1 3 also has associated with it a cam or the like 1 6 adapted to open and close contacts of a microswitch 1 7 in accordance with the position of the flap 1 The cam 16 and microswitch 1 7 are housed in switch box 1 5.

The shaft 1 3 extends through a cross bore which runs completely through the flange 1 at right angles to the axis of the flange and offset from the centre of the central orifice 3.

The cross bore is counter bored at opposite ends where it emerges from the outer face of the flange to provide a shouldered recess at each end for receiving a sealing and bearing unit. At one end the shaft 1 3 projects from the cross bore and passes into the switch box 1 5. The switch box is secured to the flange 1 by distance pieces 9 and 10.

The sealing and bearing unit at the switch box end of the shaft comprises a bearing housing 6 to fit the shouldered recess. Within the housing 6 are provided a bearing 5 and a packing ring 1 4. On the shaft between the housing 6 and the switch box 1 5 are provided a gland 7 and a water thrower 8.

At the opposite end of the shaft, the sealing and bearing unit comprises a bearing housing 23 to fit the shouldered recess. Within the housing is a bearing 5 and the housing is sealed by a blank 4.

In order to return the flap to its rest position i.e.

in line with the flange the shaft also has mounted on its end within the switch box 1 5 a pair of generally rectangular magnets 1 8a, b having rounded ends, the magnets 1 8a, b being offset relative to each other. Slightly spaced from the ends of the magnets 1 8a, b being offset relative to each other. Slightly spaced from the ends of the magnets 1 8a, b are fixed magnets 1 9. One fixed magnet 1 9 may have its south pole facing the shaft magnets 18 and the other fixed magnet 1 9 will have its north pole facing the shaft magnets.

The shaft magnets 18 will in turn have their south poles facing the north pole fixed magnet and so their north poles facing the south pole fixed magnet. The magnets 18, 19 are arranged so that their reactions will bias the flap towards its rest position.

The switch box 1 5 also includes a terminal block 22 and a cable gland 23 so that the microswitch 1 7 can be connected to some form of alarm or indicator so as to show either that fluid is flowing through the device or that fluid flow has stopped. Preferably the microswitch will be activated when the flap is in its rest position so as to indicate an alarm state, i.e. when fluid flow has stopped.

Referring to Figures 4 and 5 like parts to those of the embodiment of Figures 1 to 3 have been given the same reference numerals and for simplicity will not be described in detail except when in relation to differences between the embodiments.

The shaft 1 3 has associated with it a mild steel body 116 which when opposite inductive type proximity switch 1 17 interferes with the electromagnetic field generated by the switch 117.

The body 116 and the proximity switch 117 are housed in switch box 1 5.

The switch box 1 5 also includes a terminal block 22 and a cable gland 23 so that the proximity switch 1 17 can be connected to some form of alarm or indicator so as to show either that fluid is flowing through the device or that fluid flow has stopped. Preferably the proximity switch will be activated when the flap is in its rest position so as to indicate an alarm state, i.e. when fluid flow has stopped. Also indicated in the switch box 1 5 are relay 24, capacitor 25 and resistance 26 which are present for compatability with a particular ships alarm system. Obviously appropriate circuitry to be compatible with a particular alarm system will be chosen.

Where used in this specification the term "fluid" is intended to include air and other gases and liquids.

Claims (11)

1. A fluid flow or fluid level sensitive device comprising a part adapted to define a fluid flow orifice and having a flap-valve-like member positioned in said orifice and movable in accordance with fluid flow therethrough, and means associating said member with a fluid flow or fluid level alarm or indicating device, wherein said flap member is biased towards its rest position magnetically.

2. A device as claimed in claim 1 wherein the flap member is mounted on a shaft and the magnetic means for biassing the flap towards its rest position is associated with one end of the shaft.

3. A device as claimed in claim 2 wherein the shaft has fixed thereon a pair of magnets offset relative to each other and which are between a pair of fixed magnets.

4. A device as claimed in claim 1, 2 or 3 wherein the flap member is mounted on a shaft which has a cam associated therewith adapted to open or close contacts of a microswitch in accordance with the position of the flap member the microswitch being connected to the alarm or indicating device.

5. A device as claimed in any one of claims 1 to 4 wherein the flap member is mounted on a shaft and an alarm state position of the flap activates the alarm or indicating device without physical contact between the shaft and a switch for opening or closing the alarm or indicating device circuit.

6. A device as claimed in claim 5 wherein an alarm state position of the flap activates a proximity switch.

7. A device as claimed in claim 6 wherein the proximity switch is an inductive type.

8. A fluid flow or fluid level sensitive device comprising a part adapted to define a fluid flow orifice and having a flap-valve-like member positioned in said orifice and movable in accordance with fluid flow therethrough, and means for connecting or associating said member with a fluid flow or fluid level alarm or indicating device wherein said flap-valve-like member has a smaller surface area than that of the orifice.

9. A device as claimed in claim 8 wherein the flap member has a part of its free end angled out of line with the orifice.

10. A device as claimed in claim 8 or 9 wherein the flap member is associated with means biassing it into its rest position.

11. A fluid flow or fluid level sensitive device substantially as hereinbefore described with reference to and as illustrated in Figure 1 with Figures 2 and 3 or with Figures 4 and 5 of the accompanying drawings.