Abstract: A portable carbonating apparatus of the type comprising a pressure vessel and a header tank has a bottom inlet and a top outlet controlled by respective valve pistons which are rigidly connected together by a connecting rod.The pistons have equal areas exposed within the pressure vessel, so as to be pressure balanced at all times.The top valve piston also acts to control opening and closing of a venting port to ensure venting of pressure from a head space during initial opening movement of the valves.The header tank is self-valved and is detachable from the apparatus.