Spring-free pressure regulator with structure isolating exhaled air from valve

A spring-free pressure regulator for a breathing apparatus having a source of stored gas and a supply of carbon dioxide-free exhaled air from the user of the apparatus, the pressure regulator comprising:

• a body,
• a mixing chamber in said body for mixing the stored gas and the carbon dioxide-free exhaled air,
• a first inlet port communicating with said mixing chamber for supplying the stored gas to said mixing chamber,
• a second inlet port communicating with said mixing chamber for supplying the carbon dioxide-free exhaled air,
• a valve carried by the body, said valve communicating with said first inlet port and movable to an open position and a closed position to control the flow of stored gas to said mixing chamber, said valve being yieldably biased to the open position by the stored gas,
• means for pneumatically isolating said valve from said mixing chamber by preventing the flow of the exhaled air to said valve,
• a pressure sensing chamber operably connected to said valve and having an ambient side and a pressurized side responsive solely to pressure changes during inhaling by the user to open said valve to thereby discharge stored gas into said mixing chamber through said first inlet port and to pressure changes during exhaling by the user to close said valve to terminate the discharge of stored gas through said first inlet port, and
• an outlet carried by said body and communicating with said mixing chamber for supplying the mixture of stored gas and carbon-dioxide-free exhaled air to the breathing apparatus upon inhalation by the user.