Pump system (1) includes a centrifugal pump (2) having an inlet reser­voir (3) connected to the upstream end thereof for initially receiving the vapor/liquid mixture entering the system to allow air or vapor to separate from the liquid. Below the liquid level (L) in the reservoir is a mixing tube (25) which provides the only liquid flow path to the centrifugal pump (2). Also within the reservoir (3) below the liquid level (L) is a main ejector pump (20) which injects liquid into the mixing tube (25). The injected tube induces liquid flow from the reservoir (3) into the mixing tube (25) for flow to the centrifugal pump (2). Also, one or more vapor scavenge ejectors may be provided within the reservoir (3) to induce air or vapor from selected collected areas within the reservoir (3) and propel the air or vapor into the mixing tube (25) intermediate its length where the air or vapor is thoroughly mixed with the liquid contained therein at an intermediate pressure higher than the reservoir pressure before entering the centrifugal pump (2).