The Watts 800M4-QT 1” Bronze Anti-Siphon Pressure Vacuum Breaker helps prevent the reverse flow of polluted water from entering into the potable water supply due to backsiphonage. It consists of bronze body construction, silicone rubber check valve disc, plastic check valve seat, stainless steel springs, a bonnet with silicone rubber O-ring seal, a lightweight plastic disc float, tee handle shutoffs, and test cocks for winterization draining. The resilient sealing float o-ring and seal check disc are silicone rubber which is resistant to heat, shock and chemical attack. It is ideal in health hazard continuous pressure applications such as irrigation systems and industrial process water systems where the water enters the equipment at or below its flood rim. The maximum pressure is 150 psi (10.3 bar) and the minimum pressure is 15 psi (55kPa). From the manufacturer: This valve is for use in health hazard cross connections and continuous pressure applications.