A disposable CO.sub.2 gas generator cartridge of cylindrical construction and including inner and outer coaxial reagent chambers which are interconnected when installed in a cylindrical pressure vessel and having a top cover assembly including a pusher type activating mechanism which is operated by a cam surface located on a handwheel. The cover assembly connects to a carbonated drink dispenser by means of a quick disconnect coupling activated by the operation of a manually operated pull down lever assembly including the handwheel. Operation of the handwheel acts to start gas generation and also vent the cartridge to atmosphere when spent.