METHOD OF AND APPARATUS FOR FUNCTIONALLY TESTING A PRESSURE ACTUATED REGULATOR

Abstract

A method of functionally testing a pressure actuated regulator. The pressure actuated regulator includes a valve member arranged to open a valve aperture, and a control pressure volume in which a control pressure is set to act on the valve member. The method includes applying a force to the valve member, and taking measurements representative of the pressure of fluid in the control pressure volume and of the mass flow rate of the fluid into the control pressure volume while the force is being applied to the valve member. The method also includes isolating the control pressure volume and allowing a pressurised fluid in the control pressure volume to leak out of the control pressure volume, and taking measurements representative of the pressure of fluid in the control pressure volume while the fluid leaks out of the control pressure volume.

Claims

1. A method of functionally testing a pressure actuated regulator, wherein the pressure actuated regulator comprises a valve member arranged to open and close one or more valve apertures, and a control pressure volume in which a control pressure is set to act on the valve member, the method comprising: applying a force to the valve member, and taking measurements representative of a pressure of a fluid in the control pressure volume and of a mass flow rate of the fluid into the control pressure volume while the force is being applied to the valve member; isolating the control pressure volume and allowing a pressurized fluid in the control pressure volume to leak out of the control pressure volume, and taking measurements representative of a pressure of the pressurized fluid in the control pressure volume while the pressurized fluid leaks out of the control pressure volume; and communicating and/or storing, for assessing one or more operating characteristics of the pressure actuated regulator, the measurements taken representative of the pressure of fluid in the control pressure volume and of the mass flow rate of the fluid into the control pressure volume while the force was being applied to the valve member, and the measurements taken representative of the pressure of the pressurized fluid in the control pressure volume while the pressurized fluid was leaking out of the control pressure volume.

2. The method as claimed in claim 1, comprising depressurizing the control pressure volume before the force is applied to the valve member.

3. The method as claimed in claim 1, wherein the pressure actuated regulator comprises a biasing member arranged to apply a force to the valve member, wherein applying the force to the valve member comprises allowing the biasing member to move the valve member to increase the volume of the control pressure volume while the control pressure volume is filled from atmosphere.

4. The method as claimed in claim 1, wherein the step of applying the force to the valve member comprises pressurizing the control pressure volume.

5. (canceled)

6. The method as claimed in claim 1, wherein the force is applied to the valve member at least until the control pressure volume reaches a maximum volume.

7. The method as claimed in claim 1, wherein the pressurized fluid in the control pressure volume is allowed to leak out of the control pressure volume while the valve member is in its open position.

8. The method as claimed in claim 1, comprising venting the control pressure volume after the pressurized fluid in the control pressure volume has been leaking out of the control pressure volume for a period of time, isolating the control pressure volume, allowing the pressurized fluid in the control pressure volume to leak out of the control pressure volume after the control pressure volume has been vented, and taking measurements representative of the pressure of the pressurized fluid in the control pressure volume while the pressurized fluid leaks out of the control pressure volume.

9. The method as claimed in claim 1, comprising taking a measurement representative of a temperature of fluid in the control pressure volume while the control pressure volume is being pressurized and while the pressurized fluid is allowed to leak out of the control pressure volume.

10. The method as claimed in claim 1, wherein the one or more operating characteristics of the pressure actuated regulator that are determined include one or more of: the maximum and minimum positions of the valve member, the leakage out of the control pressure volume, and the friction of the valve member.

11. A method of determining a plurality of operating characteristics of a pressure actuated regulator, wherein the pressure actuated regulator comprises a valve member arranged to open and close one or more valve apertures, and a control pressure volume in which a control pressure is set to act on the valve member, the method comprising: determining the maximum and minimum positions of the valve member, using measurements representative of a pressure of a fluid in the control pressure volume and of a mass flow rate of the fluid into the control pressure volume taken while a force was being applied to the valve member; determining the leakage out of the control pressure volume, using measurements representative of the pressure of a fluid in the control pressure volume taken while a pressurized fluid was leaking out of the control pressure volume; and determining the friction on the valve member, using measurements representative of the pressure of the fluid in the control pressure volume and of the mass flow rate of the fluid into the control pressure volume taken while the force was being applied to the valve member.

12. The method as claimed in claim 11, wherein the minimum and maximum positions of the valve member are determined by determining the minimum and maximum volumes of the control pressure volume, and/or a leakage function of the control pressure volume.

13. (canceled)

14. The method as claimed in claim 11, wherein the friction is determined by determining a displacement of the valve member, and/or by using the measurement representative of the pressure in the control pressure volume while the force was being applied to the valve member.

15. An apparatus for functionally testing a pressure actuated regulator, wherein the pressure actuated regulator comprises a valve member arranged to open and close one or more valve apertures, and a control pressure volume in which a control pressure is set to act on the valve member, the apparatus comprising: one or more isolation valves for isolating the control pressure volume; a pressure sensor for measuring a pressure representative of the pressure of fluid in the control pressure volume; a flow rate sensor for measuring a mass flow rate of fluid into the control pressure volume; and a communication subsystem and/or a data storage for communicating and/or storing the measurements representative of the pressure and temperature of fluid in the control pressure volume; wherein the apparatus is configured to: take measurements representative of the pressure of fluid in the control pressure volume using the pressure sensor and of the mass flow rate of fluid into the control pressure volume using the flow rate sensor while a force is being applied to the valve member; close the one or more isolation valves to isolate the control pressure volume; allow a pressurized fluid in the control pressure volume to leak out of the control pressure volume, and take measurements representative of the pressure of fluid in the control pressure volume using the pressure sensor while the fluid leaks out of the control pressure volume; and communicate and/or store, for assessing one or more operating characteristics of the pressure actuated regulator, the measurements taken representative of the pressure of fluid in the control pressure volume and of the mass flow rate of the fluid into the control pressure volume while the force was being applied to the valve member, and the measurements taken representative of the pressure of the pressurized fluid in the control pressure volume while the pressurized fluid was leaking out of the control pressure volume.

16. The apparatus as claimed in claim 15, comprising a depressurization subsystem for depressurizing the control pressure volume, wherein the apparatus is configured to depressurize the control pressure volume using the depressurization subsystem before the force is applied to the valve member.

17. The apparatus as claimed in claim 15, wherein the pressure actuated regulator comprises a biasing member arranged to apply a force to the valve member, wherein the apparatus is configured to take the measurements representative of the pressure of fluid in the control pressure volume using the pressure sensor and of the mass flow rate of fluid into the control pressure volume using the flow rate sensor while the biasing member moves the valve member to increase the volume of the control pressure volume.

18. The apparatus as claimed in claim 15, comprising a pressurization subsystem for pressurizing the control pressure volume to apply the force to the valve member, wherein the apparatus is configured to take the measurements representative of the pressure of fluid in the control pressure volume using the pressure sensor and of the mass flow rate of fluid into the control pressure volume using the flow rate sensor while the control pressure volume is being pressurized.

19. (canceled)

20. (canceled)

21. The apparatus as claimed in claim 15, wherein the apparatus is configured to allow a pressurized fluid in the control pressure volume to leak out of the control pressure volume while the valve member is in its open position.

22. The apparatus as claimed in claim 15, wherein the apparatus is configured to open the one or more isolation valves to vent the control pressure volume after the fluid in the control pressure volume has been leaking out of the control pressure volume for a period of time, close the one or more isolation valves to isolate the control pressure volume again, allow the pressurized fluid in the control pressure volume to leak out of the control pressure volume after the control pressure volume has been vented, and take measurements representative of the pressure of the pressurized fluid in the control pressure volume using the pressure sensor while the pressurized fluid leaks out of the control pressure volume.

23. The apparatus as claimed in claim 15, comprising a temperature sensor for measuring a temperature representative of the temperature of fluid in the control pressure volume, wherein the apparatus is configured to take a measurement representative of the temperature of fluid in the control pressure volume using the temperature sensor while the control pressure volume is being pressurized and while the pressurized fluid is allowed to leak out of the control pressure volume.

24. The apparatus as claimed in claim 15, wherein the apparatus is configured to determine the one or more operating characteristics of the pressure actuated regulator which include one or more of: verification of fully open and fully closed positions of the valve member, an integrity of the seal of the control pressure volume, and a static and a dynamic friction of the valve member.

25. (canceled)

Description

[0105] Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0106] FIGS. 1a and 1b show examples of pressure actuated regulators that embodiments of the present invention may be used with;

[0107] FIG. 2 shows schematically an apparatus according to an embodiment of the present invention used for functionally testing pressure actuated regulators;

[0108] FIG. 3 shows a graph of an example control pressure trace during a test procedure according to an embodiment of the present invention;

[0109] FIG. 4 shows a graph of an example mass in control pressure volume trace during a test procedure according to an embodiment of the present invention;

[0110] FIG. 5 shows a graph of an example valve member displacement trace during a test procedure according to an embodiment of the present invention;

[0111] FIG. 6 shows a graph of an example effective leakage area against pressure ratio across a seal of a pressure regulator during a test procedure according to an embodiment of the present invention;

[0112] FIG. 7 shows a graph of example control pressure traces against time during a test procedure according to an embodiment of the present invention;

[0113] FIG. 8 shows a graph of an example friction against velocity of a valve member of a pressure regulator during a test procedure according to an embodiment of the present invention; and

[0114] FIG. 9 shows a graph of an example control pressure trace during a test procedure according to an embodiment of the present invention.

[0115] The present invention provides a method of and an apparatus for functionally testing a pressure actuated regulator, e.g. a pressure actuated regulator 10 as shown in FIG. 1a or FIG. 1b.

[0116] FIG. 2 shows schematically an apparatus 50 according to an embodiment of the present invention used for the functional testing of pressure actuated regulators, e.g. such as those shown in FIGS. 1a and 1b. The test apparatus 50 is arranged to be attached to the control pressure volume 24 (the “control space” as shown in FIGS. 1a and 1b) of a pressure actuated regulator 10 via a control port 26 that is fluidly connected to the control pressure volume 24 (e.g. the port 26 to which a pilot regulator (not shown) is attached during normal operation of the pressure actuated regulator 10 to set the control pressure in the control pressure volume 24). Thus, when using the test apparatus 50 shown in FIG. 2, the pilot regulator will generally be disconnected first from the control port 26. As can be seen from FIG. 2, the test apparatus 50 is housed in a known volume of pipework 51 and the pressure actuated regulator 10 being tested is in-situ in a main fluid flow line 49 through the side of which the control port 26 passes.

[0117] The test apparatus 50 includes a high pressure gas reservoir 52 (e.g. a cylinder of nitrogen gas), a first isolation valve V1 connected downstream of the high pressure gas reservoir 52, a pressure regulator PRV1 connected downstream of the first isolation valve V1, with the pressure regulator PRV1 being connected to the control port 26 of the pressure actuated regulator 10 being tested via another isolation valve V7. Two other isolation valves V2, V5 branch off the line between the pressure regulator PRV1 and the isolation valve V7; one of these isolation valves V2 is connected to a Tee valve V3 and the other isolation valve V5 is connected to a vent 54. The isolation valve V5 connected to the vent 54 is primarily for safety to allow for redundant venting of the test apparatus 50 when necessary.

[0118] The test apparatus 50 also includes a flow measurement device 56 (for measuring the flow rate {dot over (m)}(t) into the control pressure volume 24 of the pressure actuated regulator 10 being tested) connected between the Tee valve V3 and the control port 26 (and the other side of the isolation valve V7) via an orifice 58 for generating a choked flow of fluid and a further isolation valve V6. Another isolation valve V8 is connected between a vent 60 and crossing point of the lines between the isolation valves V6, V7 and the control port 26. The flow measurement device 56 is positioned to ensure optimum operation, e.g. long undisturbed pipe lengths (e.g. 20 pipe diameters) upstream and downstream of the flow measurement device.

[0119] The test apparatus 50 further includes a pressure transducer (p) 62 and a temperature transducer (T) 64 which take measurements for measuring pressure and temperature respectively from the line directly connected to the control port 26. The pressure and temperature transducers 62, 64 are positioned as close to the control port 26 as possible (to allow them to sense, as accurately as possible, the pressure and temperature of the control pressure volume 24).

[0120] A vacuum venturi 66 for generating a vacuum is connected to the other side of the Tee valve V3 from the isolation valve V2, and a further isolation valve V4 is connected between the side of the vacuum venturi 66 and the line between the Tee valve V3 and the flow measurement device 56. A vent 68 is provided on the other side of the vacuum venturi 66.

[0121] The isolation valves V1, V2, V4, V5, V6, V7, V8 and the Tee valve V3, can be controlled to open (and thus connect) or isolate different parts of the test apparatus 50 during operation, e.g. to perform different tests of the pressure actuated regulator 10 as will be described.

[0122] The (e.g. pressure, temperature and flow rate) measurements generated by the test apparatus 50 are collected and sent to a data acquisition system 70 which performs post-processing on the collected measurements to produce a report for the pressure actuated regulator 10. The data acquisition system 70 may be connected (e.g. wired or wirelessly) to the test apparatus 50 or it may be remote from the test apparatus 50.

[0123] Operation of the test apparatus 50 will now be described with reference to FIG. 2 and to FIGS. 3 to 5. FIGS. 3 to 5 show graphs of an example control pressure, an example mass in control pressure volume trace and an example valve member displacement trace respectively, taken during a test procedure according to an embodiment of the present invention.

[0124] First the test apparatus 50 is connected to the control port 26 of a pressure actuated regulator 10 (e.g. those as shown in FIGS. 1a and 1b), e.g. after the normal external control system (e.g. pilot regulator) that is normally connected to the pressure actuated regulator 10 has been disconnected and removed (after checking it is safe to do so). The test apparatus 50 is used to perform functional testing of a pressure actuated regulator. The functional testing is performed by opening and closing different combinations of the isolation valves V1, V2, V4, V5, V6, V7, V8 and the Tee valve V3, and setting different pressures using the pressure regulator PRV1.

[0125] Five general feed arrangements (i.e. combinations of valve states) are used, as shown in Table 1.

TABLE-US-00001 TABLE 1 Feed arrangements for the test apparatus. Valve V1 V2 V3 V4 V5 V6 V7 V8 Feed 1 Open Open AB Open Closed Open Closed Closed arrangement 2 Open Closed n/a Open Open Open Closed Open 3 Open Open AC Closed Closed Open Closed Closed 4 Open Closed n/a Closed Closed Closed Open Closed 5 Closed Closed n/a Closed Closed Closed Closed Intermittently opened

[0126] At the beginning of the test (in the time period t.sub.1-t.sub.2), the control pressure volume 24 is de-pressurised using the vacuum line (i.e. through the vacuum venturi 66) of the test apparatus 50 (using feed arrangement 1, Table 1) which sucks the valve member 14 of the pressure actuated regulator 10 into the nominally fully-closed position. The vacuum line of the test apparatus 50 is then disconnected from the control pressure volume 24 (using feed arrangement 2 during the subsequent time period t.sub.2-t.sub.3) and the control pressure volume 24 is slowly pressurised using the high-pressure line of the test apparatus 50 (in the time periods t.sub.3-t.sub.6), using feed arrangement 3.

[0127] During this time period, the flow rate into the control pressure volume 24 is maintained at a constant rate by choking the flow through the orifice 58, with this rate at which the control pressure volume 24 is pressurised being set by the pressure regulator PRV1. In the initial pressurisation phase (t.sub.3-t.sub.4) the control pressure volume 24 is being pressurised but the valve member 14 is yet to move; in the second phase (t.sub.4-t.sub.5) the valve member 14 is moving; in the third phase (t.sub.5-t.sub.6) the valve member 14 is in the fully open position. It is during these phases (t.sub.3-t.sub.6) that measurements (e.g. of the pressure, the temperature of the control pressure volume 24 and of the mass flow rate into the control pressure volume 24) are taken which allow the position of the valve member 14, and the friction between the valve member 14 and the stationary parts of the pressure actuated regulator 10 to be quantified.

[0128] The next period of the testing (t.sub.6-t.sub.9) is to quantify the leakage mass flow rate through the seal 28 of the pressure actuated regulator 10 at various pressure ratios. In the first part of the time period (t.sub.6-t.sub.7) the control space is quickly pressurised to the maximum rated pressure of the pressure actuated regulator 10 or the maximum pressure available to be delivered by the test apparatus 50 (whichever is smaller) using the high-pressure line (i.e. from the high pressure gas reservoir 52) and feed arrangement 4. The control pressure volume 24 is then isolated from the test apparatus 50 by closing all the isolation valves V6, V7, V8 around the control pressure volume 24 (feed arrangement 5). After an initial settling period, the pressure in the control space decays due to leakage.

[0129] After a period of time (e.g. hundreds of seconds (t.sub.7-t.sub.8)) a fraction of the pressure in the control pressure volume 24 is vented back out through one of the vents 60 in the test apparatus 50 at time t.sub.8, by opening the isolation valve V8 temporarily. Once the pressure in the control pressure volume 24 has been reduced, the isolation valve V8 is closed again. The system is then allowed to settle, with the pressure decaying again due to leakage (during the period of time t.sub.8 onwards).

[0130] This procedure of venting, settling and decaying is repeated several times until the control pressure volume 24 returns to ambient pressure (t.sub.9), shown as steps 1-5 in FIG. 3. This allows the leakage flow capacity of the pressure actuated regulator 10 to be calculated at several control space pressures while maintaining a reasonably short test time. In this embodiment, leakage is measured at five control space pressures (in other embodiments, this could be any number or, if time allows, the control space could be allowed to leak until empty without intermittent venting to find leakage across a continuous range of control space pressures).

[0131] The pressure history p(t) and temperature history T(t) of the control space, and flow rate {dot over (m)}(t) into the control pressure volume 24, is continuously recorded throughout the entire test procedure using the pressure and temperature transducers 62, 64, and the flow measurement device 56 respectively (with no mass flow rate measurements being taken during the leakage part of the test). Examples of the data taken (or calculated from) during a test procedure using the test apparatus shown in FIG. 2, when attached to a pressure actuated regulator 10 such as shown in FIG. 1a or 1b, are shown in FIGS. 3-5.

[0132] FIG. 3 shows a graph of an example control space pressure trace during the test procedure outlined above, using the different feed arrangements outlined (referred to as Feeds 1-5; see Table 1). FIG. 4 shows a graph of the trace of the mass in the control pressure volume 24 during the test procedure, estimated from the measurements taken during the test procedure. FIG. 5 shows a graph of an example cap displacement trace during the test procedure, estimated from the measurements taken during the test procedure.

[0133] After the test is complete, the external test apparatus 50 is removed from the control port 26 and the normal external control system (e.g. pilot regulator) is reconnected. Once all the data has been collected, the performance characteristics of the pressure actuated regulator 10 being tested (e.g. verification of the fully open and the fully closed positions of the valve member 14, the integrity of the seal of the control pressure volume 24, and the static and the dynamic friction of the valve member 14) can then be determined.

[0134] In one embodiment in accordance with the invention, a leakage function β(t) is calculated between times t.sub.7>t>t.sub.9, defined as:

[00001]$\begin{array}{cc}\beta \left(t\right)=\frac{1}{R\sqrt{T\left(t\right)}}\left(\frac{1}{T\left(t\right)}\frac{dT\left(t\right)}{\mathrm{dt}}-\frac{1}{p\left(t\right)}\frac{dp\left(t\right)}{dt}\right),t_7>t>t_9& \left(1\right)\end{array}$

where T(t) is the temperature measurement as a function of time (as measured by the temperature transducer 64), p(t) is the pressure measurement as a function of time (as measured by the pressure transducer 62), and R is the specific gas constant of the gas used by the test apparatus 50 in the test procedure. (Here and elsewhere, the temperature and pressure differentials may be merged into a single term,

[00002]$\frac{d}{\mathrm{dt}}\left(p\left(t\right)T\left(t\right)\right),$

e.g. giving

[00003]$\beta \left(t\right)=\frac{\sqrt{T\left(t\right)}}{Rp\left(t\right)}\frac{d}{\mathrm{dt}}\left(\frac{p\left(t\right)}{T\left(t\right)}\right).)$

[0135] The leakage function β(t) is then interpolated as a function of the pressure ratio across the seal p(t)/p.sub.ML, i.e., β(p(t)/p.sub.ML) where p.sub.ML is the mainline pressure (this may be chosen to be any suitable pressure but will generally be equal to atmospheric pressure during the test procedure).

[0136] The maximum volume (V.sub.max) of the control pressure volume 24 (the volume of everything downstream of the flow measurement device 56) when the valve member 14 of the pressure actuated regulator 10 is in the fully open position is calculated using the mass flow rate measurement {dot over (m)}(t) (as measured by the flow measurement device 56), the temperature measurement T(t) (as measured by the temperature transducer 64) and the pressure measurement p(t) (as measured by the pressure transducer 62) between times t.sub.5 and t.sub.6:

[00004]$\begin{array}{cc}{V}_{\max }=\frac{\stackrel{.}{m}\left(t\right)RT\left(t\right)}{\frac{\mathrm{dp}\left(t\right)}{\mathrm{dt}}-\frac{p\left(t\right)}{T\left(t\right)}\frac{dT\left(t\right)}{dt}+Rp\left(t\right)\sqrt{T\left(t\right)}\beta \left(\frac{p\left(t\right)}{p_{ML}}\right)},t_5>t>t_6.& \left(2\right)\end{array}$

[0137] The maximum volume (V.sub.max) may be determined through a least squares regression method, or using the average result between times t.sub.5 and t.sub.6, or any other suitable statistical method, for example.

[0138] Similarly, the minimum volume (V.sub.min) of the control pressure volume 24 (the volume of everything downstream of the flow measurement device 56) when the valve member 14 of the pressure actuated regulator 10 is in the fully closed position is calculated using the equivalent measurements of the mass flow rate measurement {dot over (m)}(t) (as measured by the flow measurement device 56), the temperature measurement T(t) (as measured by the temperature transducer 64) and the pressure measurement p(t) (as measured by the pressure transducer 62) between times t.sub.3 and t.sub.4:

[00005]$\begin{array}{cc}{V}_{\min }=\frac{\stackrel{.}{m}\left(t\right)RT\left(t\right)}{\frac{\mathrm{dp}\left(t\right)}{\mathrm{dt}}-\frac{p\left(t\right)}{T\left(t\right)}\frac{dT\left(t\right)}{\mathrm{dt}}+Rp\left(t\right)\sqrt{T\left(t\right)}\beta \left(\frac{p\left(t\right)}{p_{ML}}\right)},t_3>t>t_4.& \left(3\right)\end{array}$

[0139] Again, the minimum volume (V.sub.min) may be found through a least squares regression method, or using the average result between times t.sub.3 and t.sub.4, or any other suitable statistical method, for example.

[0140] The maximum and minimum volumes calculated are converted into displacement positions of the valve member 14 of the pressure actuated regulator 10 using:

[00006]$\begin{array}{cc}{x}_{\min }=\frac{1}{A}\left(V_{\min }-V_{\min ,\mathrm{ideal}}\right)\mathrm{and}& \left(4\right)\\ x_{\max }=\frac{1}{A}\left(V_{\max }-V_{\min ,\mathrm{ideal}}\right)& \left(5\right)\end{array}$

where x.sub.min is the valve member displacement when in the fully closed position (and should ideally be zero), x.sub.max is the valve member displacement when in the fully open position, A is the internal area within the control pressure volume 24 resolved in the direction of valve member movement over which a differential pressure acts, V.sub.min,ideal is the volume between the flow measurement device 56 and the control pressure volume 24 in the ideal fully closed position, which is estimated separately (e.g. through CAD, fitting specifications and/or calibration).

[0141] The leakage of pressure from the control pressure volume 24 of the pressure actuated regulator 10 is quantified in terms of an effective leakage area A.sub.leak as a function of the pressure ratio across the seal p(t)/p.sub.ML, which is based on the isentropic 1D compressible flow equation through a restriction:

[00007]$\begin{array}{cc}{A}_{leak}\left(\frac{p\left(t\right)}{p_{ML}}\right)=\frac{\beta \left(\frac{p\left(t\right)}{p_{ML}}\right)V_{\max .}}{{\left(\frac{p\left(t\right)}{p_{ML}}\right)}^{-\frac{\gamma +1}{2\gamma }}\sqrt{\frac{2\gamma }{R\left(\gamma -1\right)}\left[{\left(\frac{p\left(t\right)}{p_{ML}}\right)}^{\frac{\gamma -1}{\gamma }}-1\right]}}& \left(6\right)\end{array}$

where γ is the ratio of specific heats of the test fluid. The advantage of presenting the leakage as an effective leakage area is that it is nominally independent of the type of fluid being used, and therefore the test fluid need not be the same as the fluid used when the pressure actuated regulator 10 is operating normally.

[0142] The maximum and minimum displacements of the valve member 14 may then be presented (e.g. to the owner of the pressure actuated regulator), either in absolute terms, as a percentage of the ideal value, or in a converted quality scale (e.g. between 0 and 1, depending on how close the measured results are to the ideal values).

[0143] The leakage result may be shown graphically to be presented (e.g. to the owner of the pressure actuated regulator). FIG. 6 shows a graph of an example effective leakage area against pressure ratio across a seal 28 of a pressure regulator 10 during a test procedure according to an embodiment of the present invention.

[0144] In other embodiments, the effective leakage area may be calculated differently (e.g., using an incompressible flow equation rather than the compressible flow equation outlined in equation (6)). Furthermore, the effective leakage area may be presented differently, e.g. as a function of leakage Reynolds number, or as an average across all pressure ratios, or as a least-squares solution to the effective leakage area across the range of pressure ratios tested, or simplified as two values of the effective leakage area, e.g. the choked and unchoked effective leakage area.

[0145] The effective leakage area may also be converted into a subjective seal condition rating, e.g. as a percentage, or as a 0 or 1 value (e.g. a normalised “condition number”) to represent a binary “goodness” of the seal 28, such that it may be more easily interpreted by the user of the pressure actuated regulator 10. Thus the leakage may be presented in a number of different ways, e.g. in terms of flow rates at various pressure ratios, as a percentage of main flow, estimated as an effective leakage area from other fluid flow equations, as single values rather than distributions (e.g. as averages, least squares results or at a number of salient points), or as normalised “condition numbers”.

[0146] The position of the valve member 14 may be determined as a function of time by integrating the mass flow rate into the control pressure volume 24 to estimate the total mass of gas m(t) in the control pressure volume 24 between t.sub.3 and t.sub.5:

[00008]$\begin{array}{cc}m\left(t\right)={\int }_{t_3}^t\left(\stackrel{.}{m}\left(\tau \right)-\frac{\beta \left(\frac{p\left(\tau \right)}{p_{ML}}\right)p\left(\tau \right)V_{\max .}}{\sqrt{T\left(\tau \right)}}\right)d\tau +\frac{p\left(t_3\right)V_{\min .}}{RT\left(t_3\right)},t_3>t>t_5,& \left(7\right)\end{array}$

[0147] An example of this is shown in FIG. 5, which shows a graph of an example valve member displacement trace during a test procedure according to an embodiment of the present invention.

[0148] The total mass of gas in the control pressure volume 24 can then be converted into an estimate of the valve member displacement against time x(t) between t.sub.3 and t.sub.5:

[00009]$\begin{array}{cc}x\left(t\right)=\frac{1}{A}\left(\frac{RT\left(t\right)m\left(t\right)}{p\left(t\right)}-V_{\min .,\mathrm{ideal}}\right),t_3>t>t_5.& \left(8\right)\end{array}$

[0149] An example of this is shown in FIG. 6, which shows a graph of an example effective leakage area against pressure ratio across a seal of a pressure regulator during a test procedure according to an embodiment of the present invention.

[0150] The displacement history is used to estimate the friction on the valve member 14 as a function of time F.sub.friction(t) between t.sub.3 and t.sub.5:

F.sub.friction(t)=A(p(t)−p.sub.ML)−M{umlaut over (x)}(t)−KMg,t.sub.3>t>t.sub.5  (9)

where M is the mass of the valve member 14, g is the gravitational constant, {umlaut over (x)}(t) is the second temporal differential of displacement, and K depends on the orientation of the valve member 14: if the valve member 14 moves vertically and upwards through the test, K=1; if the valve member 14 moves vertically and downwards during the test, K=−1; if the valve member 14 moves horizontally, K=0. For intermediate angles, K is the resolution of the weight of the valve member 14 in the positive x direction of valve member 14 movement.

[0151] To assess the friction over a broader range of valve member 14 velocities, the portion of the testing between t.sub.3 and t.sub.5 may be repeated but at different rates of pressurisation to open the cap at varying velocities. In one embodiment, this is performed five times at different rates of pressurisation, though this may be more or less as required. The rate of pressurisation is set by adjusting the set pressure of PRV1.

[0152] Example pressure traces for each of these five runs are shown in FIG. 7, which shows a graph of example control pressure traces against time during a test procedure according to an embodiment of the present invention.

[0153] Depending on the velocity of the cap, the cap may undergo stick-slip motion (saw-tooth wave as seen in Runs 1 and 2). The friction is interpolated as a function of velocity F.sub.friction({dot over (x)}(t)) and plotted graphically. This is presented, e.g. to the owner of the pressure actuated regulator, e.g. as shown in FIG. 8 which shows a graph of an example friction against velocity of a valve member of a pressure regulator during a test procedure according to an embodiment of the present invention.

[0154] In some pressure-actuated regulators, the control pressure volume 24 may contain a biasing member (e.g. a spring) to help close the regulator 10 in no-flow conditions. In this case, the valve member position and quantification part of the test procedure starts with the control pressure volume 24 at a vacuum; and rather than filling the control pressure volume 24 using the high-pressure line of the test apparatus 50, the control pressure volume 24 is filled between t.sub.3 and t.sub.6 from atmosphere.

[0155] The equivalent pressure trace during a functional test for this kind of system is shown in FIG. 9, which shows a graph of an example control pressure trace during a test procedure according to an embodiment of the present invention. The combination of valves in the test apparatus 50 required to perform these tests is described in Tabl.

TABLE-US-00002 TABLE 2 Feed arrangements for the test apparatus, pressure-actuated regulator with spring. Valve V1 V2 V3 V4 V5 V6 V7 V8 Feed 6 Closed Closed n/a Open Open Closed Closed Closed arrangement 7 Closed Open AC Closed Open Open Closed Closed

[0156] Between t.sub.1 and t.sub.2, the control pressure volume 24 is connected to the vacuum line as described above. At the end of de-pressurisation, the control pressure volume 24 is isolated from the external test apparatus 50 and the pressures and temperatures are allowed to settle (feed 6). A vent path is then opened, in this case through V6, the orifice 58, the flow measurement device 56, the Tee valve V3 and two isolation valves V2, V5 (feed 7).

[0157] In other embodiments, this may be performed using a different arrangement of valves, but in general the flow should pass through a restriction and a flow measurement device 56 (these parts may be combined) before exhausting to atmosphere. The rate of pressurisation is controlled using the orifice 58, which may be a variable restriction such as a needle valve. The size of the restriction may be chosen according to the considerations mentioned above.

[0158] The leakage quantification is performed using the same method as described previously for the system without a spring.

[0159] Post-processing and reporting is performed using equations (1)-(8). The dynamic model of the system (equation (9)) is modified to account for the additional bias (e.g. spring) force:

F.sub.friction(t)=A(p(t)−p.sub.ML)−M{umlaut over (x)}(t)−KMg−kx(t)+F.sub.preload,t.sub.3>t>t.sub.5  (10)

where k is the spring constant, and F.sub.preload is the force on the cap from the spring, when the regulator is fully open.

[0160] It can be seen from the above that in at least the preferred embodiments of the invention, the methods and test apparatus of the present invention allow a pressure actuated regulator to be tested functionally using the test apparatus and for one or more operating characteristics to be assessed. This helps to provide a simple and repeatable test procedure to be performed on a pressure actuated regulator such that it can be checked how well the pressure actuated regulator is performing (e.g. a “health check”).

[0161] Owing, in at least preferred embodiments, to the test procedure only manipulating the control pressure volume of a pressure actuated regulator, this may not involve passing fluid through the regulator itself. Thus the method may be performed and the apparatus used on the pressure actuated regulator non-intrusively, e.g. without breaking open or pressurising the main line of the pipe or conduit in which the pressure actuated regulator is positioned.

[0162] It will be appreciated that the measurements taken and the data produced, as described above, may be analysed anywhere and by any suitable data processor. Furthermore, smoothing algorithms may be applied to the pressure and/or temperature measurements in order to improve numerical differentiation, where appropriate. The determined operating characteristics may be presented to the owner or user of the pressure actuated regulator as outlined above; however, in addition intermediate steps of testing (e.g. displacement, pressure, temperature and/or mass flow rate histories) may be presented.