Abstract: A first stage pressure regulator for use with a high pressure source of breathable gas includes a housing and means for attaching the housing to a high pressure source of breathable gas. A pressure regulated outlet is provided and a valve seat member fixed within the housing includes a central seating surface perpendicularly disposed to a longitudinal axis of the valve seat member. The perimeter of the valve seat member is shaped to enable the breathable gas to pass parallel to the valve seat member longitudinal axis in order to enable the high pressure source to be connected coaxially with the first stage pressure regulator. A piston is provided which includes a hollow center in fluid communication with the pressure regulated outlet. An open end of the piston is provided for sealing the piston against the central seating surface of the valve seat, and a spring is provided for biasing the piston in order to effect a regulated valve opening between the piston open end and the valve seat member.