A pressure tap is located on the gas turbine meter housing to enable the measurement of the static pressure upstream of the turbine wheel. It must be shut before start up and during operation, either with a screw plug or with connection to a pressure transmitter.
The pressure measurement point is marked as pr or pm (pressure at metering conditions). The bore is 3 mm and perpendicular to the wall. It has a G 1/8 cylindrical female thread and a bolting for tubing with 6 mm diameter. Connection with 6 mm stainless steel tubing (standard) or larger is recommended. If the pressure tap is not needed, it must be sealed with a G 1/8 dummy plug.
NOTE: The tubing connection of 6 mm diameter is NOT identical with 1/4” diameter tubing (6.35 mm).
Replace the inner ring or the connector if the tubing is non-metric.
The pressure reference point should be used for connecting the pressure transmitter of the flow converter or flow computer in order to convert the measured volume to base conditions, in some countries called standard or normal conditions. The pm(pr)-point is used during the determination of the meter calibration curve and this pm(pr)-point should be used for custody transfer applications. Using a different pressure point may cause
small errors in the flow measurement and the conversion to base conditions.
