Details: If you are doing deeper dives, or dives in an extended overhead environment, then you need that added time that a larger cylinder will give. The Zeagle 20 cu ft Pony Bottle System is a Totally Redundant Breathing System that includes a 20 cu ft Aluminum Cylinder, a Zeagle RaZor Regulator/Valve Combination with a 36" hose and a balanced Envoy 2nd stage.