Protective breathing aid device for diving or other operation under

Abstract

A protective exhaling device of the circulating path type with exhaling protection, with its exhaling duct connected, in the circulating path through a CO.sub.2 absorber and a gas volume equalizing chamber containing a variable volume of gas, to an inhaling duct to which there is connected a reservoir of compressed gas supplying oxygen for breathing, has a cylinder and piston unit connected to the pressure bottle pressure or to an intermediate regulator pressure for pneumatically producing a force applied to the variable volume chamber. That assures that the force determining the overpressure level is always exerted at the same magnitude independently of the amplitude of the content of the equalizing chamber of variable volume. There is an automatic switchover from overpressure operation to normal underpressure operation in the case of a major leakage. For this purpose the cylinder and piston unit is provided with an outlet valve that opens when the piston goes beyond a predetermined stroke position, so that the overpressure diminishes through the piston and at the same time the supply of pressurized gas is blocked. Thus, in the case of major leakage there is no risk that the compressed gas supply will empty quickly without the user of the apparatus noticing it. After elimination of the leak overpressure can be reinstated manually or automatically. The equipment is suitable both for diving and for compressed air breathing protection equipment generally.