GB2062812A - Valve testing - Google Patents

Abstract

Apparatus is provided for testing safety valves without interrupting normal operation of pressure systems or vessels in which they are fitted. A rigid framework (14) is located on the safety valve body (10) with access to the valve spindle (12). There is a coupling (16) between the valve spindle (12) and a connection from a force applying means (ram 22) fixed to the framework for operating the safety valve. That connection includes a stress/strain measuring device (20) from which a readout is recorded at (47) together with valve displacement from a motion transducer (30) and system/vessel pressure (from 40). A hydraulic power unit (26) includes pump, accumulator and flow and return valves, preferably also variable restriction means to control the speed of operation of the ram. Provision is also made for forced re-seating of a safety valve. <IMAGE>

Description

SPECIFICATION Valve testing The invention relates to apparatus for making checks on the functioning of valves, particularly safety valves, of pressurised systems or vessels without the complications at present involved.

Conventionally, safety valve testing, where not done by removal of the valve for bench testing, has been effected by gradually increasing the pressure within the system or vessel until either the safety valve was operated, normally movement of a poppet member against a prescribed spring force, or a maximum pressure was reached indicating failure of the safety valve.

Clearly, that must disrupt normal operation and subject the system or vessel to pressures substantially greater than normal. Other disadvantages include consequent stressing of the system or apparatus, loss of service, requirements for deliberately generating overpressures, and blocking off any other safety valves set for lower pressure operation.

Basically, it is desired herein to facilitate testing in a manner which makes no, or minimum, interference with normal service of the pressurised systems or vessels.

To this end we have devised an "on-load" type of test system wherein access is obtained to the splindle or other actuator of a valve to be tested and that spindle is then connected to a device hereof wherein load measuring means and load applying means are coupled to that spindle. In addition, it is preferred that such coupling is associated with an actuator for a displacement measuring means.

Problems arise in providing for accurate measurement of forces applied to the valve both by such test apparatus and by the system or vessel at the time concerned. Simple pressurefluid-operated piston-and-cylinder devices are not satisfactory as such devices themselves absorb some of the pressure applied and the true effective area of a piston may not be easy to ascertain.

As proposed herein, safety valve testing apparatus comprises a rigid framework for attachment to a safety valve to be tested and affording access to an actuator thereof, coupling means by which said actuator is movable, means fixed relative to said rigid framework for applying force to said coupling means via a connection therebetween, and means responsive to stress/strain in said connection for providing a signal that is a measure of force applied to said coupling means and hence to the valve actuator.

A strain gauge is suitable for said means responsive and a load cell actually interposed in the connection has proved to be particularly convenient and advantageous.

It will be appreciated that embodiments of this invention provide for direct measurement of force actually applied to the valve to be tested in a particularly reliable manner where the rigid framework ensures that the force applying means, the coupling means and the connection including the means responsive are all aligned one with another and coaxial with a valve spindle constituting said actuator.

In a preferred embodiment, of course, there is also a pressure transducer for monitoring pressure in the system or vessel with which the valve is associated. The load measuring means, displacement measuring means and pressure transducer are conveniently all electrically powered and supply their outputs to a three-pen recorder for simultaneous plotting in taking test results.

We have further found it advantageous when using an hydraulic ram to provide for adjustable restricter means so that speed of operation and/or closing of the safety valve can be controlled and adjusted to suit both of oil viscosity changes due to ambient conditions and of read out and/or recording of the desired data.

It sometimes happens that a safety valve will not readily reseat itself under its own bias, say where it is badly corroded or otherwise sticky or faulty but, nonetheless, will serve until replaced.

We thus propose further that provision is rnade for forced return of the valve by two-way pressurefluid ram operation, or by mechanical screw jacking, or by an electrically driven pressure fluid pump where conditions permit its use which will often not be the case for chemical plant.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: - Figure 1 is a diagrammatic view of a safety valve tester hereof; Figure 2 is an hydraulic circuit diagram of a power unit; Figure 3 is another hydraulic circuit diagram showing advantageous modifications; and Figures 4 and 5 show, diagrammatically, alternative provisions for forced return of the safety valve.

In the drawings, a valve 10 to be tested is shown with pressure lines into and out of it, and has a valve spindle 12 to which access is gained for testing hereof, usually simply by removing a valve cover.

A rigid rectangular frame 14 seats on the valve body to which it may be suitably secured as desired and permits access of the valve spindle 12 which is shown, at its end, with a top-hat coupling piece 1 6 attached thereto for testing. That coupling piece 16 is itself held firmly by a chuck 18 rigid, directly or indirectly, with a load cell 20 that is acted upon by an hydraulic ram 22 fixed in an upper cross-piece 24 of the frame 14.

The coupling piece 16 may have threaded engagement with the valve spindle for pushing or pulling operation depending on valve type. If only pulling is permitted, a claw-type coupling piece may be used.

The load cell 20 is conveniently of a strain gauge type using electrical resistance changes proportional to strain.

By means of the hydraulic ram 22 supplied from a hydraulic pump 26 over supply line 28 (or actuated in any other desired way) pressure can be applied to operate the valve 10 and then release gradually or as otherwise desired. In the process of that, information will be provided as to the pressure at which the valve 10 will operate, as to valve traval by means of a transducer 30 operated by an actuator 32 moving with the coupling piece 16, and as to the pressure at which the valve 10 actually closes down after being operated.

For convenience, transducer 30 is shown as a spring-loaded piston and cylinder device with the end of its piston rod operated by the part 32 moving with the coupling device 16. The body of transducer 30 is secured to the valve body in any convenient way, typically a permanent magnet 34.

Also shown in the drawing is a pressure transducer 40 in the valve feed line. Obviously any desired relationship is possible for the transducer 40 relative to the valve 10, the system or vessel associated with valve 12, and the apparatus hereof.

All of the load cell 20, the displacement transducer 30 and the pressure transducer are indicated as being electrically operated over line 42, and supply outputs over lines 44, 45 and 46 to a three-pen recorder 47. As shown, the supply 42 is indicated as being from the recorder 47, which may be battery powered.

The described system is particularly effective in testing valve operation with minimum disruption of normal operations as all that is required is access to the valve spindle and a cycle of test operation involving pressurising of, and then controlled depressurising of, the hydraulic ram 22. Then, simultaneous plots of loadings, displacement, and pressure will be obtained on the recorder 47, if desired for later detailed evaluation.

Clearly, the recorder 47 could, if desired, be replaced by a digital signal producing system so as to input directly to a computer. However, it is envisaged that the main use of this invention will be as a mobile test facility, when a permanent record from a pen recorder will normally be sufficient.

In order to avoid pulsing being recorded due to action of a pump such as 26, we actually prefer (Figure 2) to use an hydraulic powering pack 26A comprising a pump unit 48, with a return and supply reservoir 50, operating to supply an hydraulic accumulator 52 having a pressure gauge 54. Output 56 of the accumulator 52 is connected to line 28 via a valve 58 which is opened only at a prescribed value of the pressure gauge known to be adequate for operating the valve 10 to be tested.

When full displacement of the valve 1 0 has been achieved, valve 58 is shut off and valve 60 opened in line 62 returning to the reservoir 50 to plot such action as desired. Another valve 64 parallel to valve 58 is shown and serves for pressure relief purposes. That will normally be set to ensure that no valve to be tested can be damaged.

In Figure 3, similar references to those of Figure 2 are used where appropriate. It will be noted that the flow control valve 58 is associated with a specific check valve 66 before application of its output to hydraulic ram feed line 28. Downstream of the flow control valve 58, actually shown between that valve and check valve 66, is a variable orifice valve 68, usually a needle valve, to enable control of the speed of operation of the hydraulic ram for purposes aforesaid. Similarly, a variable orifice valve 70 is shown downstream of the return control valve 60. Lastly, Figure 3 shows the relief valve 64A connected across the check valve 66 and the return valves 60, 70 and a pressure gauge 72 connected thereto.

In Figure 4, a two-way hydraulic ram 22A has associated therewith a valve 74 for connecting hydraulic fluid line 28 alternatively to the underside at 76 or the other side 78 of the ram piston 80, the latter to enable forced closing of a safety valve operated by lifting of the piston 80.

Figure 5 shows an alternative forced closure arrangement using a mechanical jacking screw 82 in a cross member 84 on extensions 86, 88 of sides of the framework 14. A handwheel 90 is shown to operate the jack screw 82 which bears on an upper extension 92 of the piston of ram device 22. If preferred, cross member 84 or its equivalent bearing jack screw 82 could be secured by links 94, 96 to lugs 98, 100 on the ram 24, rather than on extensions 86, 88. In both cases, the jacking arrangement may be removable.

Provision of a forced valve return facility generally requires securement of the frame 14 relative to the valve being tested, say by suitable clamping means.

If it is desired, any slight tendency for misalignment of the items 20, 22 and 1 6 with the valve spindle 12 may be accommodated by a universal joint in the coupler 1 6. That coupler may take alternative forms suitable to particular applications, for example to be pinned, clamped or simply friction fitted to the valve spindle 1 2.

It will also be appreciated that the portable apparatus described for "on-load" testing could, where desired, also be used for bench testing purposes, say in accurately setting up a safety valve both as to release pressure, and its presetting or "blow down" pressure, the latter usually in conjunction with a compressed gas supply to the valve.

Claims (12)

1. Apparatus for making checks on the functioning of safety valves during normal operation of a system or vessel to which they are fitted, comprising a rigid framework for attachment to a valve to be tested and affording access to an actuator thereof, coupling means by which said actuator is movable, means fixed relative to said rigid framework for applying force to said coupling means via a connection therebetween, and means responsive to stress/strain in said connection for providing a signal that is a measure of force applied to said coupling means and hence to the valve actuator.

2. Apparatus according to claim 1, wherein the force applying means, the coupling means and the connection including said means responsive are all aligned one with another and (in operation) coaxially with a valve spindle constituting said actuator.

3. Apparatus according to claim 1 or claim 2, wherein the means responsive comprises a strain gauge.

4. Apparatus according to claim 1, 2 or 3, comprising displacement measuring means for providing an indication of movement of said actuator during testing of the valve.

5. Apparatus according to claim 4, wherein the displacement measuring means comprises a motion transducer securable relative to the valve, and a coupling connection to an apparatus part moved by the force applying means.

6. Apparatus according to any preceding claim, comprising a pressure transducer for providing a signal indicative of prevailing pressure on the safety valve from said system or vessel.

7. Apparatus according to claim 6 with claim 4, comprising a recorder for signals from said means responsive, said motion transducer, and said pressure transducer.

8. Apparatus according to any preceding claim, wherein the force applying means comprises an hydraulic ram connected to a power unit comprising a pump, an accumulator and valves for selecting between application of pressurised hydraulic fluid to operate the safety valve and return of hydraulic fluid.

9. Apparatus according to claim 8, wherein variable orifice flow restriction valves are associated with either or both of the valves controlling flow and return of hydraulic fluid.

10. Apparatus according to claim 8 or claim 9, comprising further valve means operative relative to alternative connections to the ram for two-way hydraulic operation thereof to enable forced reseating of a safety valve being tested.

11. Apparatus according to any one of claims 1 to 9, comprising a mechanical drive means for forced reseating of a safety valve being tested.

12. Apparatus according to claim 11, wherein the mechanical drive means includes a screw-jack operative in said rigid framework or an extension thereof for operating the force applying means oppositely to its normal operation.

1 3. Apparatus for making checks on the functioning of safety valves without interrupting operation of systems or vessels to which they are fitted, arranged and adapted to operate substantially as herein described with reference to and as shown in the accompanying drawings.