A method of attenuating pressure pulsations, comprises: pumping liquid into a vessel in fluid communication with a flow line by a conduit sealingly passing through a top surface of the vessel, so as to discharge the liquid into the flow line while creating an air-liquid interface in the vessel, by trapping in an upper part of the vessel air that attenuates pressure pulsations caused by the pumping. The method also comprises generating condition for the liquid to drain out of the vessel to allow air to fill at least the upper portion of the vessel.