What’s a pressure vacuum breaker?

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A pressure vacuum breaker (PVB) acts as a backflow preventer 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 systems are fed directly from fresh water supplies. This prevents water already in the sprinkler system from flowing back into the freshwater system. To achieve this backflow protection, pressure vacuum breakers feature a spring-loaded valve held open by fresh water pressure. In the event of a power failure, the vacuum breaker closes and prevents the contaminated water from flowing back into the drinking water circuit.

When non-potable water circuits are fed from potable water sources, the systems should be equipped with some type of backflow protection, such as a pressure vacuum breaker. These devices prevent water contaminated by chemicals, fertilizers, pesticides, or animal waste from flowing back into a freshwater source if a backflow situation occurs. Backflow occurs when the water supply is cut off or reduced resulting in a pressure drop in the supply lines. This causes any water already in the target loop to be sucked into the supply line in the same way that fluid is drawn from a straw. A pressure vacuum breaker will automatically isolate the fresh water supply in various ways if the supply pressure drop ceases altogether.

PVBs use a spring loaded poppet valve to isolate fresh water supplies. This valve is designed to be pushed open by normal system supply pressures allowing water to flow into the target circuit. Should the supply pressure drop or cease completely, the valve will close and the contaminated water will vent harmlessly onto the ground. Many of the more complex pressure vacuum breaker designs also feature valves that open simultaneously to break the siphon vacuum in the supply line as additional protection.

A pressure vacuum breaker should be installed on all water hoses or lines used for irrigation, filling swimming pools, feeding chemical or fertilizer mixers, or for applying pesticides. The PVB should be located directly after the supply tap or valve and should be the highest point in the system. In larger systems, PVBs are typically installed on every branch or section of the contaminated water system. Since the valve will periodically vent the water, it should be located where the escaping water will not cause damage. Pressure vacuum breakers should be maintained regularly and inspected for debris and valve wear, and care should be taken to protect them from freezing.

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