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A pressure vacuum breaker (PVB) serves as backflow protection device that prevents contaminated water from entering a clean water supply. Backflow protection valves are commonly used in irrigation systems where non-potable or contaminated water circuits are fed directly from fresh water supplies. This prevents the water already in the irrigation system from flowing back into the fresh water system. To achieve this backflow protection, pressure vacuum breakers are fitted with a spring loaded valve held open by the pressure from the fresh water supply. Should the supply be interrupted, the pressure vacuum breaker closes and prevents contaminated water from flowing back into the drinking water circuit.
When non-potable water circuits are supplied from drinking water sources, the systems should feature some type of backflow protection such as a pressure vacuum breaker. These devices prevent water contaminated with chemicals, fertilizers, pesticides, or animal waste from flowing back into a fresh water source if a backflow situation arises. Backflow occurs when the supply of water is interrupted or reduced with a resultant drop in pressure in the supply lines. This causes water already in the destination circuit to siphon back into the supply line in the same way that fluid is drawn up a drinking straw. A pressure vacuum breaker will automatically isolate the fresh water supply in various ways should the supply pressure drop of cease altogether.
PVBs utilize a spring loaded, poppet type valve to isolate fresh water supplies. This valve is designed to be pushed open by normal system supply pressures allowing water to flow to the destination circuit. Should the supply pressure drop or cease completely, the valve will close, and contaminated water will vent harmlessly onto the ground. Several of the more complex pressure vacuum breaker designs also feature valves which simultaneously open to break the siphon vacuum in the supply line as an added protection.
A pressure vacuum breaker should be installed on all hoses or water lines used for irrigation, filling swimming pools, supplying chemical or fertilizer mixers, or to apply pesticides. The PVB should be located directly after the faucet or supply valve and should be the highest point in the system. In larger systems, PVBs are typically installed on each branch or section of the contaminated water system. As the valve will periodically vent water, it should be located where water spillage will cause no damage. Pressure vacuum breakers should be regularly maintained and checked for debris and valve wear, and care should be taken to protect them from freezing.