Invention is of an improvement to seat of gate valves used for gas-lift producing oil wells, consisting of a seat lower part of which is curved there being a straight vertical art and a sloping straight lower part, central spacing consisting of a first part in the shape of a tapered nozzle at which gas is gradually speeded up, a second part which is the main restriction to flow, and a third part in the shape of a conical diffuser at which gas is gradually slowed down.