The Apollo® Model PVB4A and PVBLF4A Pressure Vacuum Breaker A Series prevents contamination of the potable water supply due to back-siphonage. A standard integral freeze protection relief valve serves to reduce the possibility of damage due to intermittent freezing conditions. The modular check valve cartridge provides a captured spring, a replaceable seat and a reversible silicone seat disc. This assembly features ball valve shutoffs with stainless steel handles and nuts as standard.