Series 995 Reduced Pressure Zone Assemblies were produced from 1998 - 2003. The smaller 1/2 - 1 1/2" devices are constructed of nickel plated copper tubing. The single cover provides quick, easy access to the two check modules which tread into the body. The larger 3 - 6" device is made of stainless steel. Much like the smaller devices, the larger size has a single cover with two check modules that thread into the body. The relief valve is located between the two checks and is pressurized by an external sensing line.