This invention concerns improvements in or relating to compact provers.

Compact provers are used to determine the accuracy of flowmeters, and particularly turbine, ultrasonic, coriolis and positive displacement flowmeters. Conventionally compact provers include a piston and cylinder, with fluid flowing into the cylinder moving the piston between two predetermined points. A flow computer measures the length of time taken for the piston to move between these points. The computer may also calculate any expansion in the cylinder circumference due to the internal pressure and temperature, and compensate for this. The resulting measured flow rate is verified by further piston runs to obtain a measured time within a small tolerance of repeatability.

Generally however it has not been possible to use compact provers with some meters, such as some ultrasonic flow meters for measuring very large flow rates. This is due to the fact that the compact prover would require to be excessively large due to the high flow rate.

According to the present invention there is provided a compact prover assembly, the assembly comprising two piston and cylinder arrangements, each arrangement including cylinder inlets and outlets each towards a respective end of the cylinder, a piston movable by fluid flowing through the inlet towards the outlet, means for measuring the time taken for the piston to move between predetermined points in the cylinder, with the pistons in each arrangement being mechanically interconnected so as to be simultaneously movable.

The cylinder inlets may be connected to a common fluid supply. The cylinder outlets may be connected to a common fluid output.

The piston and cylinder arrangements may be arranged in series, and may be substantially coaxial. A piston rod from a piston in one arrangement may interconnect with the piston in the other arrangement.

Alternatively the piston and cylinder arrangements may be connected together in parallel, and the pistons may be movable in parallel alignments.

More than two piston and cylinder arrangements may be provided. Where more than two piston cylinder arrangements are provided, some of the pistons may be interconnected in parallel, with others interconnected in series.

A moving arrangement may be provided for moving the pistons back towards the inlets following a time measurement. A moving arrangement may comprise a motor connected to at least one of the pistons. The motor may be connected to a one of the pistons by a cable. A tensioning arrangement may be provided to retain tension in the cable during movement thereof towards the outlets.

A valve arrangement may be provided openable when the pistons are being moved back towards the inlets, to permit fluid to flow through the cylinders.

The valve arrangement may be provided in the pistons, and may be automatically operable when the moving arrangement moves the pistons back towards the inlets. The valve arrangement may include a closure member which is spring urged to a closed position, and movable from the closed position by the moving arrangement. Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:-

Fig. 1 is a diagrammatic side view of a first compact prover according to the invention;

Fig. 2 is a diagrammatic plan view of the compact prover of Fig. 1 ;

Fig. 3 is a diagrammatic cross sectional side view of the compact prover of Fig. 1 in a first condition;

Fig. 4 is a diagrammatic cross sectional plan view of the compact prover of Fig. 1 in a second condition;

Fig. 5 is an end view of the compact prover of Fig. 1 ;

Fig. 6 is a schematic diagram of an arrangement incorporating the compact prover of Fig. 1 ;

Fig. 7 is a diagrammatic side view of a second compact prover according to the invention; and

Fig. 8 is a diagrammatic side view of a third compact prover according to the invention.

Figs. 1 to 4 of the drawings show a compact prover 10 suitable for determining the accuracy of a high flow flowmeter. The prover 10 includes two piston and cylinder arrangements 12, 14 which are similar in most respects. Each arrangement 12, 14 includes a steel cylinder 16 with an inlet 18 and outlet 20. The inlets 18 are both connected to a common fluid supply, and the outlets 20 are also both connected to a common fluid output. Each cylinder 16 locates a respective piston 22, and the pistons 22 are interconnected by a piston rod 24. Each piston 22 has a selectively openable valve 26 for a purpose hereinafter to be described.

The left most cylinder 16 may have a rounded end at its downstream end, whilst the right hand cylinder 16 as shown has a withdrawal arrangement 28 at its right hand side as shown in Fig. 1. The arrangement 28 includes a motor 30 with a cable 32 which connects to the right hand piston 22. The cylinders 16 are mounted on supports 34 located on a skid 36, which skid 36 also mounts the moving arrangement 28 in a cover 38.

Each valve 26 has a central closure member 40 selectively movable to close an opening 42 in an annular member 44, with the closure member being spring urged to close the opening 42. Fig. 3 shows the valves 26 closed, and Fig. 4 shows the valves 26 open.

In use, the compact prover 10 is used to measure the accuracy of a flowmeter as follows. Fluid passes from the outlet of a meter to be proved into the cylinders 16 through the inlets 18 and moves the pistons 22 to the left as shown in the drawings, with fluid eventually exiting the cylinders 16 through the outlets 20 and returning back to the common meter outlet stream.

The time taken for the pistons 22 to move between two fixed positions is accurately measured, and any expansion in the cylinder circumference due to internal pressure and temperature is measured and used as a compensation in respect of this time. This process is repeated on a number of occasions, and the data collated.

To move the pistons 22 back upstream, the motor 30 is actuated which initially causes the valves 26 to be opened to allow fluid to flow past the pistons 22, and the cable 32 then pulls the right hand piston 22 into position.

This causes the left hand piston 22 to be moved into position by virtue of the interconnecting piston rod 24. The open valves 26 mean that fluid flow through the cylinders 16 is not affected by the movement of the pistons 22 in an upstream direction. For the next measurement the valves 26 are reclosed. During the time measurement a tension may be maintained in the cable 32. This can be achieved using a servo motor or a tensioning wheel arrangement, and prevents the winch which mounts the cable 32, from overturning.

There is thus described a compact prover which permits the accuracy of a high volume flow rate flowmeter to readily be checked. By virtue of the twin piston and cylinder arrangements in series, the compact prover is relatively small and is thus a practical proposition in situations where existing compact provers would not be so.

Fig. 6 is a diagram showing use of the compact prover 10 for determining the accuracy of four meters 46 arranged in parallel in a fluid supply with an inlet stream 48 and an outlet stream 50. Isolation valves 52,

54 are provided respectively upstream and downstream of each of the meters

46.

Branches 56 including isolation valves 58 are provided downstream respectively of each of the meters 46, but upstream of the respective isolation valves 54. The branches 56 interconnect, and connect to the two inlets 18 of the compact prover 10. Further branches 60 extend from the outlets 20 of the compact prover 10, and connect via an isolation valve 62 to the outlet stream 50.

Fig. 7 shows a second compact prover 64. The compact prover 64 is similar in many respects to the compact prover 10 and again includes two piston and cylinder arrangements 66, 68 similar to the arrangements 12, 14. In this instance the arrangement 66, 68 are connected in parallel with their piston rods 70 interconnected by a cross member 72. The cross member 72 connects to the cable 32 extending from the motor 30. The compact prover 64 operates in a similar manner to the prover 10, with the cross member 72 ensuring that the two piston and cylinders 66, 68 operate simultaneously.

Fig. 8 shows a third compact prover 74. Here four piston and cylinder arrangements 76, 78, 80 and 82 are provided. As shown in Fig. 8, the uppermost arrangements 76, 78 are connected in series in a similar arrangement to the prover 10, by a connecting rod 84. Similarly the lowermost pair of arrangements 80, 82 are connected in series by a connecting rod 86. The connecting rods 84, 86 are interconnected by a cross member 88 at their right hand ends as shown in Fig. 8, which is again connected to the cable 32. The third compact prover 74 will again operate in a similar manner to the provers 10 and 64, and provides for particularly effective space saving.

Various other modifications may be made without departing from the scope of the invention. For instance, other numbers of piston and cylinder arrangements could be provided in a compact prover, connected in parallel and/or series.. A different form of connection could be used. A different moving arrangement could be used. A different piston arrangement could be used. Whilst the above described compact prover is usable for determining the accuracy of flowmeters, such provers could be used in a number of different applications.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.