Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
  • G01F25/10—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of flowmeters
  • G01F25/11—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of flowmeters using a seal ball or piston in a test loop

Definitions

• the conventional form of meter prover utilises the passage of a sphere along an accurately dimensioned pipe between fixed detectors to displace a known volume of fluid.
• the volume of fluid displaced by the prover passes in series through the meter to be proved and the number of pulses generated in the meter during the passage of the sphere between the detectors is counted to enable determination of the k factor.
• a large displaced volume is essential and provers of 20 metres in length were not uncommon. Provers of this size are clearly impractical on oil rigs and in other confined spaces and efforts have therefore been made to develop so-called compact provers.
• annular piston sealing means It is of course critical that there should be no leakage passed the annular piston sealing means and a practice has developed of providing two spaced sealing rings with means for detecting encroachment of fluid within the annular chamber defined by the sealing rings.
• This detection means usually requires the presence of an axial bore along at least one piston rod communicating with a leak detector.
• Bi-directional meter provers are useful in that they maximise the number of proving runs that can be made in any time interval but do involve the duplication of certain components and also require valve arrangements for reversing flow through the prover. Such valve arrangments must of course be shown to be leak-proof and at larger prover sizes this may become prohibitively expensive.
• Uni-directional meter provers are provided with auxiliary means for returning the piston to a start position.
• This may comprise a slave piston and cylinder or, in larger sizes, a simple winch.
• Both uni and bi-directional provers require a very accurately machined prover bore of a significant length. This - as will be evident - is both expensive to manufacture and demanding of the support structure, if dimensional stability is to be assured over a range of working temperatures and pressures. There is a further difficulty, not previously appreciated, that will arise with many uni-directional provers. If a piston rod, or some other means of communication with the piston, is provided at one side only of the piston, it will usually be the case that on movement of the piston 10 different volumes of fluid are displaced upstream and downstream of the piston. This may introduce errors into the flow measurement, as will be described.
• the meter to be proved is connected in parallel with a section of the working fluid flow path but normally isolated through valves.
• the valves are so operated that the entire flow passes through the prover with the piston of course moving in synchronism with that flow, over the length of its stroke. If unequal volumes of fluid are displaced upstream and downstream of the piston, there will be an instantaneous change - and usually an increase - in the flow rate out of the prover. In a typical installation, the flow downstream of the prover may have a substantial mass and such an instantaneous flow change may have significant shock effects.
• flow meters of the type which are to be proved in way generall have characteristics which are not totally independent of the flow rate.
• the present invention consists, in one aspect, in a meter prover for proving a flow meter in a fluid path, comprising an inlet chamber having an inlet; an outlet chamber having an outlet and communicating with said inlet chamber through an aperture, the prover being adapted for connection with the inlet and outlet in series with the meter to be proved, and a displacement body movable in sealing engagement through said aperture on entry of fluid into said inlet chamber to displace a corresponding volume of fluid from the outlet chamber, the amount of movement of the displacement body being an accurate measure of flow through said meter; a flow path through said displacement body to enable a flow to be established for the inlet to the outlet chamber prior to movement of the displacement body and means for selectively blocking said flow path.
• communication means are connected with the displacement body and extend through the inlet or outlet chamber to enable exterior communication with the displacement body, the fluid volume displaced by that portion of the communication means contained within the said chamber increasing on movement in one sense of the displacement body, there being provided compensation means extending from the displacement body through the same said chamber such that the fluid volume displaced by that portion of the compensation means contained within the said chamber decreases as the displacement body moves in said one sense, whereby communication is made at one side only of the displacement body whilst maintaining equal flow displacements upstream and downstream of the displacement body.
• the communication means comprise first shaft means extending from the displacement body and wherein the compensation means comprise second shaft means extending from the displacement body.
• the dimensions of the first and second shaft means are so selected to satisfy the condition of equal flow displacement upstream and downstream of the displacement body.
• the first shaft means comprises a single shaft extending along the axis of the displacement body and the second shaft means comprises two shafts equal in aggregate cross sectional area with the first shaft and both extending parallel to the first shaft.
• the present invention consists in a further aspect in a meter prover for proving a fluid flow meter, comprising chamber means arranged for fluid flow therethrough in series with the meter; a body movable in sealed engagement within the chamber means in synchronism with fluid flow therethrough; means for launching the body into said flow and means for continuously monitoring the position of the body within the chamber means; wherein said means *for ' launching the body is so controlled in response to the meter output and the instantaneous velocity of the body as derived from said position monitoring means as to bring the body to the velocity associated with that flow through the chamber existing prior to launching of the body.
• said launching means are controlled in response to a delayed meter output signal.
• said launching means comprises a hydraulic linear actuator.
• Figures 2 and 3) through a meter prover according to this invention Figure 2 is an axial section on line B-B of Figure 1
• Figure 3 is an axial section on line C-C of Figure 1
• Figure 4 is a block diagram illustrating the instrumentation which is associated with the meter prover of Figure 1.
• the meter prover shown generally at 10 comprises a base plate 12 to which the remaining components are bolted or otherwise suitably secured.
• An aperture plate 14 is arranged generally centrally of thebase plate and 12 has an aperture 16 aligned coaxially with the axis of the prover shown at 18.
• a cylindrical outlet sleeve 20 is secured through welds 22 to the aperture plate and, as seen best in Figure 3. is positioned eccentrically of the prover axis 18.
• An outlet port 2k extends radially from the sleeve 20 in the region of maximum offset from the prover axis.
• the outlet sleeve 20 is , closed at the end remote from the aperture plate by an end plate 26 so defining a cylindrical outlet chamber shown at 28.
• an inlet sleeve 30 of similar length to but of larger diameter than the outlet sleeve 20.
• the inlet sleeve 30 " is arranged coaxially wj.th the prover axis and is secured to the aperture plate 14 through a substantial flange 32.
• the inlet sleeve 30 is closed at its free end by an end plate 34 to form an inlet chamber shown at 36-
• An inlet port 38 communicates with this chamber, there being provided inwardly of the chamber an arcuate baffle plate 4 ⁇ which opposes the inlet port 38.
• a displacement body shown generally at 42 is arranged for sliding movement through the aperture 16.
• the displacement body comprises a displacement tube 44, the outer cylindrical surface of which is in complementary engagement with the aperture 16.
• the aperture 16 is provided with two bearing collars 46 and with two annular sealing arrangements 48.
• a channel 50 in the aperture plate 14 enables exterior sensing of the fluid pressure in the annular chamber defined between the two sealing arrangements 48.
• a cylindrical buoyancy member 52 Within the displacement tube 44, there is positioned a cylindrical buoyancy member 52. This buoyancy member is sealed and is aligned coaxially with the displacement tube. A radially outwardly directed flange 54 on the buoyancy member 5 is bolted or otherwise suitably secured to an inwardly directed flange 6 on the displacement tube. At the end of the buoyancy member remote from the aperture plate, two ears 8 provide a mounting for one end of a communication shaft 60. This shaft 60 extends through an aperture 62 in the end plate 34 and forms part of a hydraulic linear actuator shown schemmatically at 64.
• This track is supported at one end on the aperture plate 16 through anchorage 88 and at the other end from the end plate 26 through cranked support member 90.
• the rider 84 and track 86 together form a length encoder which may take a variety of known forms.
• the function of the length encoder is to provide an electrical signal indicative of the position of the displacement body.
• the displacement tube 44 is provided with an array of apertures 98 in the region between the free end of the displacement tube and the flange 54.
• the diameters of the apertures 98 decrease in the array in the axial direction away from the aperture plate 14.
• a similar ring of apertures 100 is provided towards the opposite end of the displacement tube.
• a processor receives inputs both from the length encoder comprising rider 84 and track 86 and from the meter to be proved.
• a controller for the linear actuator 64 also receives the meter output together with a signal from the length encoder which represents the instaneous velocity of the displacement body.
• the manner of operation of the described meter prover can now be understood.
• the prover inlet 38 and outlet 24 are connected through suitalbe valves with the fluid path containing the meter, such that when it is desired to initiate a proving operation, the prover may be connected in series with the meter.
• fluid will pass through inlet port 38 into the chamber 36, escaping through apertures 98 to the interior of the displacement tube 44 downstream of flange 54 and thereby to the outlet chamber 28 and outlet port 24.
• linear actuator 64 is caused to move the displacement body to the right as shown in Figure 1.
• apertures 8 are gradually closed with the fluid pressure acting upon the displacement body increasing until a point at which all of the apertures 98 have passed into the aperture 16.
• the controller for the linear actuator is arranged so that a fixed and predetermined force is applied to the displacement body.
• a sufficient force is applied to the displacement body to bring it into synchronism with the true fluid flow, that is to say the flow that would pass through the prover in the absence of the displacement body.
• the controller comparing a signal from the meter to be proved with a signal from the length encoder which represents the velocity of the displacement body. Since the displacement body may initially be responsible for a slowing down of the meter, the signal which is taken is representative of the flow rate immediately before the proving run is initiated. At the beginning of this second phase the velocity of the displacement body will ordinarily be less than that associated with true fluid flow rate. The controller therefore ensures that a sufficient force is applied to the displacement body to bring it to the correct velocity. This done, the third phase is entered in which the displacement body moves in synchronism with the unperturbed fluid flow and a corresponding volume of fluid will be displaced from the outlet chamber 28 through the port 24.
• the hydraulic pressure in the actuator is maintained constant and the processor is arranged to carry out the proving function by comparison of the known movement of the displacement body with the meter output.
• the processor is arranged to carry out the proving function by comparison of the known movement of the displacement body with the meter output.
• baffle plate 14 opposite the inlet port 38 reduces the risk of a side loading on the displacement body through the velocity head of the inward fluid flow.
• the baffle plate dissipates the energy of the incoming flow and helps to direct the flow equally around the circumference of the displacement body.
• the critical engagement is between the exterior of the displacement tube 44 and the aperture 16 with its bearing collars 46 and seals 48.
• the outer surface of the displacement tube 44 must be accurately cylindrical to within the same limits as the bore of a conventional compact prover but the skilled man will appreciate that the operation of forming an external cylindrical surface to within close tolerances is markedly simpler than is the case with an internal cylindrical surface or bore.
• the bore of a conventional compact prover is usually subject to the pressure and temperature of the fluid on its interior surface but to ambient, or at least some other pressure and temperature on its external surface. In the case of the displacement tube 44, this is totally immersed within the fluid and is not subject to distortion through differential pressure or temperature effects.
• a meter prover according to this invention will be shorter than many conventional provers of equivalent capacity. This is likely to be particularly the case with larger bore sizes where the flanges required at both ends of the prover cylinder may add considerably to the overall length. It will be appreciated that in the described prover, the size of flange 3 is not a critical factor in determining overall length.
• the linear acuator 64 and length encoder are effectively combined in one device.
• the hydraulic actuator then takes the form of a generally conventional hydraulic cylinder having a linear displacement transducer mounted within the piston rod.
• the transducer comprises fixed and movable coils and provides an output signal through mutual inductance.
• rider 84 and track 86 are no longer required.
• the one device can not only drive the displacement body at the correct velocity but also provide the positional information required by the processor. If fixed volume proving is used, the device is required merely to indicate when the displacement body passes the start and finish points; the displaced volume during this travel being an accurately known constant.
• the advantages offered by the compensating rods 78 have been fully described. It should.be noted that a single compensating shaft of. appropriate cross-sectional area or indeed other forms of compensating shaft means could alternatively be used. In a more radical modification, the compensation meas may take forms other than shaft means. The important feature is that the changing volume displaced by the rod 60 (or indeed other means of communication with the displacement body) should be compensated for by a change in volume displaced by the compensation means. If the communication means are more conveniently positioned in the outlet rather than in the inlet chamber, the position of the compensation means will similarly be reversed. The manner in which side loading of the displacement body in the outlet chamber is reduced by eccentric mounting of the outlet chamber should be regarded as one example only of a technique of radial balancing.

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• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Measuring Volume Flow (AREA)

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• 1985
  • 1985-05-31 GB GB858513783A patent/GB8513783D0/en active Pending
• 1986
  • 1986-05-30 WO PCT/GB1986/000305 patent/WO1986007146A1/en not_active Application Discontinuation
  • 1986-05-30 AU AU59527/86A patent/AU5952786A/en not_active Abandoned
  • 1986-05-30 EP EP86903493A patent/EP0223813A1/de not_active Withdrawn

Non-Patent Citations (1)

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