Series N9-CD Field Testable Dual Check Vacuum Breakers with Atmospheric Vent prevent high-hazard backsiphonage backflow and low-head backpressure (10 ft. or less) from contaminating the potable water supply. It prevents backflow associated with hose connections when screwed directly to a sill cock, yard hydrant, or wall hydrant. It consists of a brass body construction with two independently operating rubber and stainless steel check valves, with an atmospheric vent located between the them. Series N9-CD is in-line field testable, non-removable and designed for non-continuous pressure applications. It is ideal for installation in service sinks, chemical dispensers, sill cocks, and frost-proof hydrants. Series N9-CD-C comes with chrome plating. Maximum Working Pressure: 125psi (10.6 bar).