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.low pressure loss documented by independent approval agenciesbuilt-in freeze resistance feature standardeasily removable modular check valve cartridgecaptured stainless steel springsball valve shutoffs w/ SS handles and nuts standardtest cocks located for easy drainingcorrosion resistantunique canopy detachmentvertical up / horizontal installation