The Principle of the Storage Tank Breather Valve
During the operation of atmospheric pressure and low-pressure storage tanks, the gas inside the tank often expands or contracts due to changes in the liquid level inside the tank or changes in the external temperature. As a result, the pressure of the gas phase inside the tank also fluctuates. The fluctuation of the gas pressure can easily cause the tank to be overpressurized or in a vacuum state. In severe cases, it may lead to the tank bulging due to overpressure or collapsing due to low pressure.
In order to prevent the storage tank from being in an unstable state such as overpressure or negative pressure, in the process design, a breather valve is usually installed on the tank roof to maintain the air pressure balance of the storage tank, ensure that the storage tank is not damaged when it is overpressurized or in a vacuum state, protect the safety of the storage tank, and reduce the volatilization and loss of the materials inside the tank, which plays a certain role in promoting safety and environmental protection. Generally, breather valves or a combination of breather valves and flame arresters are used on the roofs of fixed-roof storage tanks, and on the floating roofs of internal floating-roof and external floating-roof storage tanks. The main purpose of the breather valve is to protect the storage tank. When the pressure inside the tank reaches a certain value, the breather valve opens to ensure that the tank will not be overpressurized, thus achieving the purpose of protecting the tank. The main purpose of the flame arrester is to prevent the storage tank from catching fire. When a fire breaks out outside the storage tank (or at the breather valve), the flame arrester can prevent the flame from entering the interior of the storage tank through the pipeline, thereby avoiding an explosion.
The internal structure of the breather valve is essentially composed of a pressure valve disc (i.e., the exhalation valve) and a vacuum valve disc (i.e., the inhalation valve). The pressure valve disc and the vacuum valve disc can be arranged side by side or overlapping. Its working principle is as follows: When the pressure inside the storage tank is equal to the atmospheric pressure, the valve discs and valve seats of the pressure valve and the vacuum valve fit closely, and the sealing structure beside the valve seat has an "adsorption" effect, making the valve seat tightly sealed without leakage. When the pressure inside the tank rises to the set pressure value, the pressure valve is opened, and the gas inside the tank is discharged into the outside atmosphere through the exhalation valve (i.e., the pressure valve) side. At this time, the vacuum valve is in a closed state due to the positive pressure inside the tank. Conversely, when the pressure inside the tank drops to a certain vacuum degree, the vacuum valve is opened due to the positive pressure of the atmospheric pressure, and the outside gas enters the tank through the inhalation valve (i.e., the vacuum valve) side. At this time, the pressure valve is in a closed state. At any time, the pressure valve and the vacuum valve cannot be opened simultaneously. When the pressure or vacuum degree inside the tank drops to the normal operating pressure state, the pressure valve and the vacuum valve are in a closed state, and the exhalation or inhalation process stops.
