pressure type vacuum breaker

a device to prevent backflow caused by back-siphonage, which incorporates a force loaded ventilation valve, and operates automatically to admit air into the downstream chamber of the valve whenever the pressure in the chamber reduces to 7 kPa

see mechanical backflow prevention device

device to prevent backflow caused by backsiphonage, which incorporates a force loaded ventilation valve, which operates automatically to admit air into the downstream chamber of the valve whenever the pressure in the chamber reduces to 7 kPa

pressure type vacuum breaker