Series 757a, 757Na Double Check Valve Assemblies prevent the backflow of pollutants that are objectionable but not toxic, from entering into the potable water supply. Its compact housing consists of two independently operating bi-link check valves, two shutoff valves, and four test cocks. It features a stainless steel housing and sleeve and is 70% lighter than traditional designs. Series 757a, 757Na is designed for non-health hazard applications and may be installed under continuous pressure service to protect against both backpressure and backsiphonage. Maximum Working Pressure: 175psi (12.06 bar).