WO2001069197A1

WO2001069197A1 - Measuring with a flow restrictor the pressure at which a pneumatic device (piston, valve) starts to move

Info

Publication number: WO2001069197A1
Application number: PCT/GB2001/000692
Authority: WO
Inventors: Colin RENDLE
Original assignee: Furness Controls Limited
Priority date: 2000-03-14
Filing date: 2001-02-19
Publication date: 2001-09-20
Also published as: GB0006060D0; GB2361771A; AU3389401A

Abstract

A test system for measuring the pressure applied to a pneumatic apparatus including a moveable part (13) at the time at which the moveable part begins to move, which system comprises a means to apply air from pressure air supply (17) via a flow restrictor (16), and a pressure transducer (19) connectable to measure the pressure of air supplied to the pneumatic apparatus.

Description

MEASURING WITH A FLOW RESTRICTOR THE PRESSURE AT WHICH A PNEUMATIC DEVICE ( PISTON , VALVE ) STARTS TO MOVE

BACKGROUND OF THE INVENTION

The present invention relates to apparatus and method for measuring the pressure at which a pneumatic device starts to move

During the manufacture of pneumatic devices which have one or more moveable parts, it is necessary to perform various tests These tests include a test to determine the actual pressure required to start moving the or one of the moveable parts Examples of such devices include, amongst others, the piston in a piston/cylinder assembly, the moving part of a pneumatically operated valve and the opening or closing of a relief valve

Hitherto, the measurement of the pneumatic pressure required to start moving a moveable part of a pneumatic device has been done manually This manually operated test may be accomplished by observation or by touch on the moveable part if that part is visible or can be touched whilst the pressure is changed In fact the human finger, for example, is quite sensitive to movement and so movement of the moveable part can be readily detected by, say, a human finger if the part is accessible The pressure is then noted at which the moveable part starts to move

The obvious way to automate this process would be to provide some kind of mechanism for measuring movement of the moveable part, in other words to replace the finger or eye This involves providing a means of determining the start of movement either by contact or non-contact sensor on the moveable part One difficulty in providing a suitable sensor for this task lies in the fact that the test item, such as a piston/cylinder assembly, may be anything from one centimetre in diameter and a few centimetres long to thirty or more centimetres diameter and several metres long The initial movement of the moveable part, therefore, may be very slow in the case of a large cylinder or very rapid in the case of a small cylinder (although it is not of course always so restricted)

Furthermore, measuring movement of the moveable part of the pneumatic device would normally mean that something has to be attached to the moveable part and this is invasive It would be preferable to provide an arrangement in which no modification or amendment to the pneumatic device is required

The present invention removes the need for either a contact or non-contact sensor on the moveable part

SUMMARY OF THE INVENTION

According to a first aspect the present invention provides a test system for measuring the pressure applied to a pneumatic device including a moveable part at which the moveable part begins to move, which comprises a pressure air supply which may be a fixed pressure air supply, a flow restrictor, and a pressure transducer connectable to measure the pressure of air supplied to the pneumatic assembly

The pressure transducer may provide means to display or indicate when there is a discontinuous change of pressure The pressure transducer may be connected to a logic system to measure rate of change of pressure and to measure deviations in the rate of change of pressure

According to a second aspect, the present invention provides a test system for measuring the pressure applied to a pneumatic apparatus including a moveable part at the time at which the moveable part begins to move, which system comprises means for providing air at a pressure which steadily changes with time, and a pressure transducer connectable to measure the pressure of air supplied to the pneumatic apparatus According to a third aspect, the present invention provides a method for measuring the pressure applied to a pneumatic apparatus including a moveable part at the time at which the moveable part begins to move, comprising: applying air at a steadily changing pressure and measuring the pressure of air supplied to the pneumatic apparatus.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the invention will now be described by way of example only and with reference to the accompanying drawing which shows a pneumatic apparatus including a moveable part and a test system for measuring the pressure applied to that moveable part at the point when the moveable part begins to move.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing, there is shown a pneumatic apparatus 10 in the form of a piston 11/cylinder 12 assembly, the piston 11 being mounted to a rod 13. Pressure air is supplied to the cylinder 12 via a line 14.

In a prior arrangement, the pressure air is pumped via line 14 into the cylinder 12, and a finger is applied to the rod 13 to determine when the rod 13 begins to move. At that point the pressure may be measured by means of a normal pressure transducer.

In the present arrangement, however, the line 14 is connected to a flow restrictor 16 which in turn is connected to high pressure air reservoir 17, the air being pressurised by means of a pump 18. A pressure transducer 19 is connected to the line 14 between the cylinder 12 and the flow restrictor 16, and the pressure transducer is connected to a logic system 21. A control stop valve 22 is provided in the line 14 between the flow restrictor 16 and the high pressure air reservoir 17. At the start of the test the pressure in the cylinder 12 is normally but not necessarily the ambient pressure. When the control stop valve 22 is opened, it allows pressurised air from the reservoir 17 to pass to the flow restrictor. The air flows through the restrictor 16 and the pressure starts to change in the cylinder 12. This pressure change is measured by the pressure transducer 19. The pressure rises steadily in the cylinder

12 until the moveable part, for example the piston 11, starts to move. At this point the pressure no longer changes steadily as before. It may continue to change at a different rate, it may remain constant or it may even change in the opposite direction. In whichever case the logic system 21 connected to the transducer 19 recognises the deviation in the rate of change of the pressure and records the pressure at which this change occurred. This is the pressure which the test is designed to determine, ie the pressure at which the moveable part (piston 11) of the pneumatic apparatus 10 begins to move. This pressure may be referred to as the 'lift-off pressure of the moving part of the pneumatic apparatus.

This system is capable of determining this 'lift-off pressure for any pneumatic device where a moving part starts to move at a certain pressure.

Whilst we have described above the apparatus operating with an increasing pressure and a reservoir 17 of pressurised air, in some circumstances the system may work in the opposite direction, that is, the reservoir 17 may be below ambient pressure, typically a vacuum, and the cylinder 12 may, in operation, have a reduced pressure applied to it. In that case of course the pressure will be negative with respect to the starting pressure. The pressure may be either positive or negative with respect to the starting pressure in the device.

The invention is not restricted to the foregoing example.

Claims

1. A test system for measuring the pressure applied to a pneumatic apparatus including a moveable part at the time at which the moveable part begins to move, which system comprises a means to apply air from pressure air supply via a flow restrictor, and a pressure transducer connectable to measure the pressure of air supplied to the pneumatic apparatus.

2. A test system as claimed in claim 1 wherein the pressure transducer includes means to display or indicate when there is a discontinuous change of pressure.

3. A test system as claimed in claim 2 in which the pressure transducer includes a logic system to measure rate of change of pressure and to measure deviations in the rate of change of pressure.

4. A test system as claimed in any of claims 1 to 3 in which said pressure air supply comprises a supply of air at greater than ambient pressure.

5. A test system as claimed in any of claims 1 to 3 in which said pressure air supply comprises a supply of air at less than ambient pressure.

6. A test system for measuring the pressure applied to a pneumatic apparatus including a moveable part at the time at which the moveable part begins to move, which system comprises: means for providing air at a pressure which steadily changes with time, and a pressure transducer connectable to measure the pressure of air supplied to the neumatic apparatus.

7. A method for measuring the pressure applied to a pneumatic apparatus including a moveable part at the time at which the moveable part begins to move, comprising: applying air at a steadily changing pressure and measuring the pressure of air supplied to the pneumatic apparatus.

8. A method as claimed in claim 7 including measuring a discontinuous change in the air pressure.

9. A method as claimed in claim 7 or 8 including steadily increasing the pressure of air.

10. A method as claimed in claim 7 or 8 including steadily decreasing the pressure of air.