The working principle of breathing valves - atmospheric and low-pressure storage tanks are common equipment in the process industry. During the use of atmospheric and low-pressure storage tanks, the expansion or contraction of gas inside the tank is often caused by changes in liquid level or external temperature, as well as pressure changes inside the tank. The gas phase in the storage tank fluctuates accordingly. Fluctuations in gas pressure can easily cause tank overpressure or vacuum, and in severe cases, tank overpressure swelling or low-pressure collapse.
The working principle and installation of the breathing valve To prevent unstable states such as overpressure or negative pressure in the tank, the process design usually adopts the method of installing a ventilation valve at the top of the tank to maintain the gas pressure balance of the tank, ensure that the tank is not damaged by overpressure or vacuum, protect the safety of the tank, reduce the volatilization and loss of materials in the tank, and promote safety and environmental protection. It is usually used in conjunction with a ball valve.
The internal structure of a breathing valve mainly consists of a pressure valve plate (i.e. exhalation valve) and a vacuum valve plate (i.e. inhalation valve). Pressure valve plates and vacuum valve plates can be arranged side by side or overlapping. Its working principle: When the pressure in the storage tank is equal to atmospheric pressure, the valve discs of the pressure valve and vacuum valve are tightly matched with the valve seat, and the sealing structure on the side of the valve seat has an "adsorption" effect, making the valve seat sealed. When the pressure or vacuum increases, the valve disc begins to open. Due to the "adsorption" effect still present at the edge of the valve seat, good sealing performance can still be maintained.
Breathing valve structure diagram
When the pressure inside the tank rises to a constant pressure, the pressure valve opens and the gas inside the tank is discharged into the outside atmosphere through the exhalation valve (i.e. pressure valve). At this point, due to the positive pressure inside the tank, the vacuum valve is closed. On the contrary, when the pressure inside the tank drops to a certain degree of vacuum, due to the positive pressure of atmospheric pressure, the vacuum valve opens, and external gas enters the tank through the suction valve (i.e. vacuum valve), at which point the pressure valve closes. At no time should the pressure valve and vacuum valve be opened simultaneously. When the pressure or vacuum inside the tank drops to the normal working pressure, the pressure valve and vacuum valve close, and the exhalation or inhalation process stops.
The function of the breathing valve
The ventilation valve plays a sealing role under normal circumstances. The breathing valve can only operate under the following conditions:
(1) When the storage tank outputs materials, the breathing valve begins to suck air or nitrogen into the tank.
(2) When filling the tank with material, the breathing valve begins to exhale the gas inside the tank.
(3) Due to climate change and other reasons, the vapor pressure of the materials inside the tank increases or decreases, and the breathing valve exhales steam or inhales air or nitrogen gas (usually referred to as thermal effect).
(4) When a fire occurs, due to the heat of the exhaled gas inside the tank, the evaporation of the liquid inside the tank will increase sharply, and the breathing valve will start to exhale outside the tank to avoid damage to the tank due to overpressure
(5) In other operating conditions, such as pressurized transportation of volatile liquids, chemical reactions between internal and external heat transfer devices, operational errors, etc., the breathing valve should exhale or inhale accordingly to avoid damage to the storage tank due to overpressure or vacuum.
Principle of breathing valve
General standards
The general standards for breathing valves include:
SY/T 0511.1-2010 Petroleum Storage Tank Accessories Part 1: Ventilation Valve
TB/T 3319-2013 Railway Tank Car Respiratory Safety Valve
QC/T 1064-2017 Road Transport Flammable Liquid Hazardous Materials Tank Vehicles Breather Valve
DIN EN 14595-2016 Dangerous goods transport tank operating devices - Pressure and vacuum breathing valves