GB2198239A

GB2198239A - Monitoring fluid pressure in a flexible pipe

Info

Publication number: GB2198239A
Application number: GB08628703A
Authority: GB
Inventors: John Ernest Elsom Sharpe
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1986-11-27
Filing date: 1986-11-27
Publication date: 1988-06-08
Also published as: ES2008358A6; WO1988004042A1; GB8628703D0

Abstract

In order to measure fluid pressure in a flexible pipe (20), the pipe is squashed between two jaws (12, 14) joined by a bridge (16). The compression of the pipe between the jaws causes a strain to be set up in the bridge which can be measured by a strain gauge (28, 30) connected to the bridge. As the internal pressure in the pipe changes, so the strain detected by the strain gauge will change and this produces an output representative of the pressure variations in the pipe. The temperature of the pipe contents can also be monitored by temperature readings taken from the pipe exterior.

Description

Monitoring Fluid Pressure in a Flexible Pipe This invention relates to the monitoring of the state of a fluid in a flexible pipe by a non-invasive technique. The parameters to be monitored include the fluid pressure, and the pipe may be, for example a radiator hose of a motor car through which cooling fluid flows. The invention relates in particular to a monitoring method and to a device which assists such monitoring.

cording to first aspect of the invention, there is provided a method of monitoring fluid pressure in a flexible pipe, wherein the pipe is mounted between two opposei jaws so that the pipe diameter is distorted, the jawC being connected to one another by a bridge so that the bridge is placed in strain when the distorted pipe is positioned between the jaws, and the incremental strain produced in the bridge by changes in the internal pressure in the pipe is observed.

This method allows a non-invasive monitoring to take place without any difficulty in setting up of equipment.

The method may N also be adapted to monitor fluid temperature by detecting temperature variations exhibited at the exterior pipe surface.

Strain produced in the bridge may be detected on a shear diaphragm incorporated in the bridge and on which strain gauges are mounted.

According to a second aspect of the invention, there is provided a device for monitoring fluid pressure in a flexible pipe, t-he device comprising two opposed jaws between which the pipe can be placed, a shear bridge connecting the jaws and a strain gauge associated with the bridge, wherein the spacing between the jaws is less than the normal diameter of the pipe such that the pipe has to be quashed to fit between the jaws whereby changes in pressure in a fluid passing through the pipe cause the force exerted by the pipe on the jaws to be varied thus producing a variation in.the strain existing in the bridge which strain is measured by the strain gauge to give a reading representatlve of fluid pressure iI1 the pipe.

The jaws may be connected to one another by two bridges or, preferably, by one bridge. When there is only one bridge, ,ioining adjacent ends of the two jaws, the other ends of the jaws can provide a gap into which the pipe can be introduced. Thus the device can be made without any r. < rt. Tl.e jw & e pruferaLly parallel.

It is also possible for the device to be used to monitor the temperature of the fluid in the pipe. h thermocouple or thermistor or other temperature sensitive probe can be mounted on one or other of the jaws in an insulated pocket sn es to be in t]lermel contact with the exterior pipe surface. In an alternative embodiment, the strain gauges themselves may sense temperature changes.

The bridge nay haNe locally thinned portions which concentrate the strain into a shear diaphragm located in a bore extending through the bridge, with the axis of the tore at right angles to the extent of the jaws. The diameter and position of the bore are such that the locally thinned portions are diametrically opposite regions which have equal thicknesses and are also thinner than any other part of the wall, so that the greatest strain is directed through these regions. The bore is she as being cylindrical, but could however be of any regular shape.

The shear diaphragm is preferably circular and is located in the bore with its plane at right angles to the bore axis. Strain gauges can be mounted on both sides of the diaphragm. There may be, on each side, one, two or four sucli gauges. If there are two gauges, they will measure strain at 45 to the load axis and at right angles to one another. The diaphragm can be formed out of the material of the block, by counterboring the bore from opposite sides of the bridge. Alternatively, a separate diaphragm can be bonded in place.

The jaws and the bridge can be made in a single piece of material, but it may be more practical to make one Jaw and the bridge out of a first piece of material and the other jaw out of a second piece of material. It is important that the jaw material should be at least stiffer than the flexible pipe, 50 that pressure changes in the flexible ripe are transmitted thrc.uEh the jaws to the bridge rGt]-ler than being absorbed in distortion of the jaws.Where temperature is also to be monitored, it is Important that the material of the jaw carring the probe allows heat conduction to the probe, but is otherwise thermally insulating.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a device in accordance with the invention; Figure 2 is a side view of the device of Figure 1; Figure 3 is a section through the device on the line III-III from Figure 2; Figure 4 is a side view of a second embodiment of a device according to the invention; and Figure 5 is a side view of a third embodiment Ci a device according to the invention.

Figure 1 shows a one-piece device 10 with an upper jaw 12 and a lower jaw 14. The jaws are connected by a bridge 16.

A cylindrical bore 18 is formed in the bridge and a shear diaphragm 52 which responds t.o changes in the strain experienced by the bridge is located in the bore.

In use, a flexible pipe 20, shown by dotted lines in Figure 1, is introduced between the jaws, and the ends of the jaws are tapered to help the pipe to be positioned.

Tflc gap between the jaws is related to the diameter of the pipe such that the pipe has to be squashed to fit between the jaws. Pest results are obtained if the pipe i5 squashed a substantial amount and takes up an oval shape as shown in Figure 1. However useful readings can still be obtained with much smaller amounts of squashing, so that one device can be used to take readings from pipe of different nominal diameters.

The upper jaw 12 is connected to the bridge 16 through a connection region 22, and the bore 18 is positioned and dimensioned so as to leave two narrow wall regions 24 and 26 above and below the diaphragm. 32.

Tie presence of a pipe 20 between the jaws introduces a strain mto tic device and tends to push the jaws apart.

This strain is transferred to the wall regions 24 and 26 which are the thinnest parts of the bridge joining the jaws and from these wall regions to the diaphragm 32. As the internal fluid pressure inside the pipe 20 changes, so the force exerted by the pipe on the jaws changes, and the strain appearing in diaphragm 32 changes.

The strain in the diaphragm 32 is measured by strain gauges 28 and 30 mounted on the diaphragm, as can be seen in Figures 2 and 3. The two strain gauges are mounted with their effective directions at right angles to one another and at t5 to the wall regions 24 and 2G, ie at 45" to the load axis. The strain gauges will be connected , through wires 34 which pass out of the bore 18 through access holes 36, to conventional circuitry which enables a reading of the applied strain to be displayed. The reading can be zeroed when the device is first applied to a pipe, and any movement from the zero setting will then correspond to a change in the internal pressure in the pipe.For a particular pipe in a particular system, it may be possible to calibrate the strain gauge readings so as to give a direct reading of the actual fluid pressure in the pipe. In most Instances however, all that will be needed is comparative reading, > ie that the pressure has increased or decreased relative to a datum point.

The paths along which pressure is applied through the wall regions 24 and 26 to the diaphragm 32 are shown in Figure 2 tiy heavy, chain-dotted lines. The ends of the bore 18 can be filled, after the strain gauges have been mounted on the diaphragm 32, with a flexible filler material which will prevent damage to the gauges but which will not affect the mechanical properties of the bridge. Silicone rubber would be suitable.

In addition to monitoring the pressure in the pipe 20, the device can be used to additionally monitor the temperature of the fluid in the pipe. This is done by introducing a thermocouple, thermistor or other temperature sensitive probe through an insulated pocket in one of the jaws so that it is in heat-conducting contact with the exterior wall surface of the pipe. The upper jaw has a bore 38 into which the thermocouple is inserted. The inside face of the upper jaw should have a thermally conductive surface between the thermocouple tip and the place where it will be in contact with the tube wall.The thermocouple can, like the strain gauge outputs, be connected into a conventional evaluation circuit which allows variations in temperature to be monitored - Figure 3 shows with dotted lines an indication of a thermally insulating coating 39 on the two jaws 12 and 14 Figure 4 shows an alternative construction where the two jaws are made separately and are then rigidly connected together. This can have two main advantages. Firstly it considerably eases manufacture. Secondly it allows the two jaws to be rade from different materials.The upper jaw 12a can be made of an insulating material, so that heat is not conducted away Iron. the thermocc)uI)le in the bort- 38a, but it will be necesary to have a conducting plate 40 on the inner lace of the jaw so that a pipe can be positioned anywherein in the jaw gap and still be in thernal contact with the thermoccuple.

The two jaws 12a and 14a are connected by two bolts 42 which securely and rigidly fix the jaws together. The embodiment shown in Figure 4 also has a recess 44 for accommodating the evaluation circuitry which processes the strain gauge signals.

The embodiment shown in Figure 5 has a first jaw 50 and a second jaw 52 pivoted to the first jaw by a hinge 54. In use, a pipe in which the pressure is to be monitored is introduced between the two jaws and the top jaw is then lowered so that the pipe is squahed between the jaws. A nut 56 is then tightened onto a stud 58. Changes in fluid pressure in the pipe will produce changes in the strains experienced in two bridges 60 and 62 at opposite ends of the jaws, and these strain changes will be evaluated in the same way as described for the earlier embodiments.

In practice, the pipe can be positioned anywhere between the jaws; it makes no difference whether the pipe is nearer to the bridge or further from it, the readings produced will be the same as it is a force which is being measured.

In one practical device based on the embodiment shown in Figure 1, an output from the strain gauges of 2OmV was equivalent to a pressure change in the pipe of 1 atmophere, and a device with a jaw gap of 15 mm was capable of monitoring pressures in pipes of from 25 to 40 diameter.

The device described can find many applications. One such application is in testing the cooling system of a motor vehicle, and in particular operation of the thermostat.

Devices as described can be fitted on appropriate uses on all sides of the therr.icstGt and the er,gine can thrn be run to cycle the cooling system. A predeterminable sequence of pressure changes in the hoses will be noticed if the thermostat is operating correctl and is opening and closing at the right times. If this sequence does not occur, then the cooling system is faulty due, for example, to an inoperative thermostat, an airlock or a blockage in the system.

It is an important feature of the system that it can be directly connected to existing engine diagnostic equipment.

Another possible modification to the device can make it possible to measure temperatures through the same strain gauge which measures pressure changes. Strain gauge operation is temperature dependent. If all the components between the pipe and the strain gauge are thermally conductive, then the temperature at which the strain gauge operates will follow the exterior temperature of the pipe, which itself follows the internal pipe temperature.

If the strain gauge characteristics are known, it may be possible to obtain both pressure and temperature outputs from the gauges.

Claims

1. A method of monitoring fluid pressure in a flexible

pipe, wherein the pipe is mounted between two opposed jaws so that the pipe diameter is distorted, the jaws being connected to one another by a bridge so that the bridge is placed in strain when the distorted pipe is positioned between the jaws, and the incremental strain produced in the bridge by changes in the internal pressure in the pipe is observed.

2. h device for monitoring fluid pressure in a flexible pipe, the device cor.;pri.t.ing two posed jaws between which the pipe can be placed, a bridge connecting the jaws and a strain gauge associated with the bridge, wherein the spacing between t.he ,jaws i 5 less than the normal diameter of the pipe such that the pipe has to be squashed to fit between the jaws whereby changes in pressure in a fluid passing through the pipe cause the force exerted by the pipe on the jaws to be varied thus producing a variation in the strain existing in tha bridge which strain is detected by the strain gauge to give a reading representative of fluid pressure in the pipe.

3. A device as claimed in Claim 2, wherein the jaws are connected to one another by two bridges such that the jaws span a gap between the bridges.

4. h device as claimed in Claim 2, wherein the jaws are connected to one another by one bridge which joins adjacent ends of the two jaws, with the other ends of the jaws defining a gap into which the pipe can be introduced.

5. A device as claimed in any one of Claims 2 to 4, wherein the jaws are parallel.

6. h device as claimed in any one of Claims 2 to 5, including means for monitoring the temperature of the fluid in the pipe.

7. A device as claimed in Claim 6, wherein the temperature monotoring means is a temperature sensitive probe mounted on one or other of the jaws so as to be in thelrnl contact with tie exterior pipe surface.

8. A device as claimed in Claim 6, wherein the temperature monitoring means are the strain gauges t ec.

9. A device as claimed in any one of Claims 2 to 8, wherein the bridge has locally thinned portions where the strain can be measured.

10. A device as claimed in Claim 9, wherein a cylindrical bore is driven through the bridge with the axis of the bore at right angles to the extent of the jaws and the diameter and position of the bore such that the wall surrounding the bore has two diametrically opposite regions which have equal thicknesses and are also thinner than any other part of the wall, so that the greatest strain can be measured there.

11. A device as claimed in Claim 10, wherein a diaphragm is located in the bore with its plane at right angles to the bore axis and a strain gauge is mounted on the diaphragm.

12. A device as claimed in Claim 11, wherein strain gauges are mounted on both sides of the diaphragm, there being two strain gauges on each side arranged to measure strain at 45" to the load axis and at right angles to one another.

13. A device as claimed in Claim 11 or Claim 12, wherein the diaphragm is formed out of the material of the block, by counterboring the bore from opposite sides of the diaph-aEr:l.

14. h device as claimed in Claim 11 or Claim 12, wherein a separate diaphragm is bonded in place in the bore.

15. A device as claimed in any one of Claims 2 to 14, wherein the jaws and the bridge are made in a single piece of material.

16. A device as claimed in any one of Claims 2 to 14, -wherein one jaw and the bridge are made together out of a first piece of material and the other jaw out of a second piece of material.

17. h method of monitoring fluid pressure in a flexible pipe substantially as herein described with reference to the accompanying drawings.

18. A device for monitoring fluid pressure in a flexible pipe substantially as herein described with reference to any one embodiment shown in the accompanying drawings.