The present invention relates to a method for pumping gas-liquid mixtures and to a piston pump characterised in that a gas-liquid mixture is fed into a working chamber during the suction stroke and the compression stroke of the gas, wherein said mixture is fed through a hydraulic channel from an area located at the outlet of a discharge valve of said working chamber. The hydraulic channel is formed in the closure member of the discharge valve and comprises a separator, a filter, a throttle with adjustable hydraulic resistance as well as an insert with an axial opening and a radial opening.