Breathing Valve
The breathing valve is an essential component installed on oil and liquid storage tanks to regulate positive and negative pressure within the tank, facilitating the ingress and egress of liquids. Without a breathing valve, the movement of liquids in and out of the tank would be impeded. Atmospheric and low-pressure storage tanks are common in process industries. During operation, changes in the liquid level or external temperature can cause the gas inside the tank to expand or contract, leading to fluctuations in gas-phase pressure. Such fluctuations may result in overpressure or vacuum conditions, potentially causing structural damage to the tank.
To prevent such instability, process designs typically incorporate a breathing valve at the top of the tank to maintain pressure equilibrium, ensuring the tank remains intact during overpressure or vacuum conditions. This protects the tank's safety and reduces material volatilization and loss, thereby promoting safety and environmental protection.
Principle of Operation
The internal structure of the breathing valve consists of a pressure valve disc (exhalation valve) and a vacuum valve disc (inhalation valve), which can be arranged side by side or overlapping. When the tank pressure equals atmospheric pressure, both valve discs seal tightly against their seats, maintaining a secure seal. As pressure or vacuum increases, the valve discs open, allowing for controlled gas exchange while maintaining a good seal due to the "adsorption" effect on the seat sides.
Functions of the Breathing Valve
Under normal conditions, the breathing valve maintains a sealed environment. It activates under specific conditions:
1. When materials are discharged from the tank, the breathing valve allows air or nitrogen to enter.
2. During material filling, the breathing valve expels gas from the tank.
3. Climate changes or other factors affecting vapor pressure cause the breathing valve to exhale vapor or inhale air or nitrogen.
4. In case of fire, increased heat causes rapid vaporization, prompting the breathing valve to release gas and prevent overpressure damage.
5. Other operational scenarios, such as pressurized transport of volatile liquids or chemical reactions, also trigger the breathing valve to prevent overpressure or ultra-vacuum damage.
Installation Considerations
1. Install the breathing valve at the highest point of the tank's gas phase space to minimize evaporation loss and provide a direct passage.
2. For large or critical tanks, install two breathing valves with different pressure gradients to ensure redundancy and reduce failure risk.
3. If the required breathing volume exceeds the capacity of a single valve, install multiple valves symmetrically on the tank top.
4. For nitrogen-sealed tanks, position the nitrogen supply pipe nozzle away from the breathing valve interface and insert it approximately 200mm into the tank to ensure effective nitrogen sealing.
5. Consider the pressure drop caused by flame arresters to avoid overpressure.
6. In regions where the average temperature of the coldest month is ≤0°C, implement anti-freezing measures to prevent valve disc freezing or blockage, avoiding overpressure or vacuum issues.
