Abstract: A vessel to be vented on a discontinuous basis is connected by first conduit means, containing a first valve means, to the inlet of a compressor. An equalization chamber is connected by second conduit means, containing a second valve means, to the first conduit means at a point between the first valve means and the inlet of the compressor. The valves are selectively actuated to initially connect the vessel and the equalization chamber to permit the gas pressures therein to equalize then to close off the chamber while the compressor withdraws additional gas from the vessel until the desired pressure is reached, and finally to withdraw gas from the chamber. The equalization chamber and compressor can be employed to sequentially vent a plurality of vessels. A control means can be utilized to perform the selective actuation of the valves.