How the breathing valve works

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How the breathing valve works-Atmospheric and low pressure storage tanks are common equipment in process industry. During the use of atmospheric and low-pressure storage tanks, the expansion or contraction of the gas in the storage tank is often caused by the change of the liquid level in the storage tank or the change of the external temperature, and the pressure of the gas phase in the storage tank fluctuates accordingly. The fluctuation of the gas pressure is very easy to cause overpressure or vacuum in the storage tank, and in serious cases, overpressure bulging or low-pressure collapsing of the storage tank.

Working principle and installation of breather valve

In order to prevent the tank from overpressure or negative pressure and other unstable conditions, the process design usually adopts the method of installing a breather valve on the top of the tank to maintain the gas pressure balance of the tank, ensure that the tank is not damaged in overpressure or vacuum, protect the safety of the tank, and reduce the volatilization and loss of materials in the tank, which plays a certain role in promoting safety and environmental protection.

The internal structure of the breathing valve is essentially composed of a pressure valve disc (i.e. exhalation valve) and a vacuum valve disc (i.e. suction valve). The pressure valve disc and the vacuum valve disc can be arranged side by side or overlapped. Its working principle: when the pressure of the storage tank is equal to the atmospheric pressure, the valve disc and the valve seat of the pressure valve and the vacuum valve are closely matched, and the sealing structure on the side of the valve seat has “adsorption” effect, so that the valve seat is tight. When the pressure or vacuum increases, the valve disc starts to open. Since there is still “adsorption” effect on the valve seat edge, it can still maintain good sealing.

Structure diagram of breather valve

When the pressure in the tank rises to the constant pressure, the pressure valve is opened, and the gas in the tank is discharged into the outside atmosphere through the exhalation valve (i.e. pressure valve). At this time, the vacuum valve is closed due to the positive pressure in the tank. On the contrary, when the pressure in the tank drops to a certain vacuum, the vacuum valve is opened due to the positive pressure of atmospheric pressure, and the external gas enters the tank through the suction valve (i.e. the vacuum valve), and the pressure valve is closed at this time. At any time, the pressure valve and the vacuum valve cannot be opened at the same time. When the pressure or vacuum in the tank drops to the normal operating pressure, the pressure valve and the vacuum valve are closed, and the exhalation or inhalation process is stopped.

Function of breathing valve

The breather valve plays a sealing role under normal conditions. The breather valve can only work under the following conditions:

(1) When the storage tank outputs materials, the breathing valve starts to suck air or nitrogen into the tank.

(2) When filling materials into the tank, the breathing valve starts to exhale the gas in the tank to the outside.

(3) Due to climate change and other reasons, the vapor pressure of materials in the tank increases or decreases, and the breathing valve exhales steam or sucks air or nitrogen (usually called thermal effect).

(4) In case of fire, the liquid evaporation in the tank will increase sharply due to the heat of the exhaled gas in the tank, and the breathing valve will start to exhale out of the tank to avoid damage to the tank due to overpressure.

(5) Under other working conditions, such as pressurized transmission of volatile liquid, chemical reaction of internal and external heat transfer devices, operation error, etc., the breathing valve shall exhale or inhale accordingly to avoid damage to the storage tank due to overpressure or vacuum.

Principle of breathing valve

Common standards

Common standards for breathing valves are:

SY / T 0511.1-2010 petroleum tank accessories Part 1: breather valve

TB / T 3319-2013 breathing safety valve for railway tank car

QC / T 1064-2017 breathing valve of tank type vehicles for road transport of flammable liquid dangerous goods

DIN EN 14595-2016 operating device pressure and vacuum breathing valve of dangerous goods transport tank

Installation drawing of breather valve