I. Meter Prover Definition Liquid meter provers are defined as a “known traceable volume” which is used to verify and establish a meter factor during actual flowing and operating conditions. (Traceable to NIST) II. Types of Conventional Meter Provers  A.  Bidirectional Prover (pipe prover): A positive displacement type prover with flow and displacer traveling in both directions by means of a 4-way diverter valve.  B.  Unidirectional Prover (pipe prover): A positive displacement type prover with flow and displacer traveling always in one direction, by means of a transfer chamber, or interchange. C.  Volumetric Tank Prover: As the name implies, this prover is a calibrated tank or vessel with a sight gauge and scale to read a metered volume. The flow must be stopped to determine the volume. III. Operating Principle of a Positive Displacement Meter Prover A bidirectional prover will be used as the example of most items. (Please see the drawing on page 7) A.  To prove a meter, flow is established through the meter, then downstream to the prover via the prover manifold valves. B.  Flow goes into the 4-way diverter valve and forces a sphere displacer into the pipe section, which seals against the pipe walls. C.  The base volume of a bidirectional prover is expressed as the sum of the calibrated volumes between detectors in two consecutive one-way passes in opposite directions, each corrected to standard temperature and pressure conditions. 2350 Industrial Road, Sapulpa, OK 74066 • Main: 918-445-1141 • sales@weamco.com Bulletin MPD-112 Toll Free: 800-331-3790 • Fax: 918-445-4617 • www.weamco.com 5-19 Page 1 of 8 Meter Factor =  Actual Volume (Prover) Metered Volume (Meter) Meter Prover Design and Construction