Oxygen system for parachuting

An oxygen system supplies either 100% oxygen to a demand valve in a mask or pulses of oxygen to the mask. Switching is automatic during a parachute descent. The system includes a valve manifold that is responsive to ambient pressure such that at low pressures it is configured to deliver gas from either an oxygen cylinder or an aircraft supply line to the mask demand valve and at higher pressures it is configured to deliver gas from the cylinder to a pulse gas delivery system. The mask also includes an inhalation valve that is closed if oxygen is supplied to the demand valve. Otherwise, the inhalation valve opens to allow ambient air to be drawn in and the pulse gas delivery system delivers a pulse of oxygen in response to the onset of inhalation.