Breathing valve is fixed at the top of tank ventilation devices to ensure that the tank pressure normal. Tank prevent overpressure or vacuum tank so that suffered damage, but also to reduce the loss of volatile liquid storage tank. 
     According to the "Petrochemical design of fire safety regulations" (GB50160-92) states : "A B liquid fixed roof tanks, should be established and the two semi-breathing valve, "Sierp company developed SB-type series of new products, complete with specifications, compact, light weight, the ventilation, leaking small advantages. Products are called single valve, single-suction valve, breathing valve structures can form combinations with fire retardant structure, also preparation for the takeover.