The breathing valve is a safe and energy-saving product that maintains the air pressure balance of the storage tank and reduces the volatilization of the medium. The breathing valve makes full use of the pressure bearing capacity of the storage tank to reduce the medium discharge. The principle of the breathing valve is to use the weight of the positive and negative pressure valve disc to control the positive exhaust pressure and the negative suction pressure of the storage tank. When the pressure of the medium in the tank is within the control operating pressure range of the breathing valve, the breathing valve does not work to maintain the airtightness of the oil tank; when the medium is added to the tank, the pressure of the gas space in the upper part of the tank rises to achieve breathing When the valve is operated with positive pressure, the pressure valve is pushed open, and the gas escapes from the exhalation port of the breathing valve, so that the pressure in the tank does not continue to increase; when the medium is drawn out of the tank, the pressure in the upper gas space in the tank drops, reaching the breathing valve. When the negative pressure of the tank is operated, the atmosphere outside the tank will open the negative pressure valve disc of the open breathing valve, so that the outside air will enter the tank, so that the pressure in the tank will not continue to drop, and the air pressure inside the tank and outside the tank will be balanced. safety device to protect the tank.