The breathing pipe of the air compressor is called the breathing valve, and only the piston type air compressor has the breathing nozzle. Function of the breathing nozzle of the air compressor: release and absorb the air in the crankcase of the air compressor. When the air compressor is working, a little air comes in and out of the breathing mouth. It is a safe and energy-saving product used to maintain the air pressure balance of the tank and reduce the volatilization of the medium. It makes full use of the pressure bearing capacity of the tank itself to reduce the discharge of its medium. When the medium is pumped out of the tank to reduce the pressure of the upper gas space in the tank and reach the operating negative pressure of the breather valve, the atmosphere outside the tank will open the negative pressure valve disc that opens the breather valve, allowing the outside gas to enter the tank, so that the pressure in the tank will no longer continue to drop, and the pressure inside the tank will be balanced with that outside the tank to protect the safety device of the tank.