BV-100 Breather Valve

Pressure / vacuum relief valves or breather valves are special types of relief valves which are specifically  designed  for tank protection. The range  includes pressure only, vacuum only and combined pressure / vacuum valves, all available with flanged outlets or vented to atmosphere Pressure / vacuum relief valves are used extensively on bulk storage tan s, including fixed roof tanks with floating covers, to minimize evaporation loss. The valves prevent the buildup of excessive pressure or vacuum which can unbalance the system or damage the storage vessel.

The range inClUdes pressure only, vaCuum only and combined Pressure/Vacuum Valves, all available with flanged outlets or vented to atmosphere. Pressure/Vacuum Relief Valves are used extensively on Dulk storage tanks, including fixed roof tanKs with floating covers, to minimize evaporation loss. Pressure/vacuum relief valves  prevent emission  losses until very close to the set pressure, and prevents air intake until very close to the set vacuum.

The geometry of the valves has been developed in order to optimize overall performance in terms of high flow capacity, set pressure, sealing and re-sealing.

Working principle
The Breather Valve is a protection device mounted on a nozzle opening on the top of a fixed roof atmospheric storage tank. Its primary purpose is to protect the tank against rupturing or imploding. Without an opening or a controlled opening, a fixed roof atmospheric tank would rupture under increasing pressure caused by pumping liquid into the tank or as a result of vapor pressure changes caused by severe thermal changes. Imploding, or the collapsing of a tank, accurs during the pumping out procedure ar thermal changes. As the liquid level lowers, the vapor space pressure is reduced to below atmospheric pressure.

This vacuum condition must be alleviated through a controlled opening on the tanK. In short, the tank needs to breathe in order to eliminate the possibility of rupturing or imploding. Because of its primary function, this Valve is called Breather Valve. Valve selection should be in accordance with American Petroleum Institute Standard API 2000 or other applicable standard. The modular nature of valves means they can be tailored to meet specific customer’s requirements: whether this is pressure or vacuum-protection only; or vapours and gases either piped-away or vented to atmosphere. A weather-hood protects the pressure vent port is fitted to prevent intrusion of foreign matter into the valve i.e. rain, sand,birds etc..

Figures 1 and 3 – indicate the position of both the pressure and vacuum disc, when tank and atmospheric pressure are equal. i.e. both discs are fully seated.

Figures 2 – snows the position of both discs, as set pressure is reached, with escaping vapour IiRing the pressure disc and holding the vacuum disc closed.

Figures 4 – shows the position of both disc, as set vacuum is reached, with atmospheric pressure lifting the hinged vacuum disc to allow ingress of air into the tank, whilst holding the pressure disc closed.