When the pressure at the pump inlet is constantly greater than the atmospheric pressure and the saturated vapour pressure of the liquid, and there is no gas separator, a gas extractor or special gas extractor shall be necessary if gaseous formations are liable to occur between the pump and the meter during non-flow periods or if air pockets can be introduced into the pipework (e.g. when the supply tank is completely empty) in such a manner as to produce a specific error in excess of 1 % of the minimum delivery.
