Self-contained breathing apparatus

Abstract

A Self-Contained Breathing Apparatus with automatic redundant fluid pressure controls and a facemask mounted low pressure warning device. The apparatus utilizes two stages of pressure regulation wherein the final stage is the demand regulator that delivers the breathing gas to the wearer. The first state includes a pair of pressure regulators connected in parallel with different outlet pressures, both of which reduce the pressure of the stored supply gas to pressures compatible with the second stage breathing demand regulator. A primary regulator in the first stage delivers a low output pressure to the second stage demand regulator. In the event of a 'failure closed' condition of the primary regulator an automatic transfer valve switches on the backup regulator and communicates its slightly higher outlet pressure to the demand regulator. A warning that the supply pressure has been depleted to a predetermined low level is also provided by a supply pressure actuated transfer valve which transfers the output of the first stage pressure regulators from the primary to the backup regulator thereby activating a whistle alarm device in the facemask to which the demand regulator is also mounted. The whistle is activated by the higher outlet pressure from the backup regulator during the inhalation phase of each breath in either of the two events of a 'failure closed' condition of the primary regulator or the depletion of the supply pressure to a dangerously low level.