Abstract: On the suction side of its pump housing a pump is provided with a gas separator optionally built integrally with the pump housing. The gas separator comprises a cyclone chamber with an inlet channel for a gas or air-containing pump medium, and a liquid outlet channel connected to the inlet of the pump. A bleed housing is provided at the upper end of the cyclone chamber, said bleed housing comprising an air duct. The air duct is substantially Z-shaped and of a cross section deviating from circular shape. The air duct comprises furthermore a relatively wide groove over at least a portion of its length and at its upper wall. The groove extends from adjacent the inlet of the air duct and forwards into said duct. In this manner a separation of gas or air from the gas or air-containing pump medium is obtained which is more reliable than the previously known separation.