The 2 1/2" Ames 4000SS Series Reduced Pressure Zone (RPZ) backflow preventer began production in 1990 and is still currently in production. The body is contructed of stainless steel and uses a single victaulic coupler cover. The 4000SS utilizes plastic cam checks and a self contained stainless steel relief valve. The relief valve may be removed from the body by unthreading it, but use caution when doing so, as to not "squeeze" or warp the RV body. The cam checks thread into the body. Although not necessary, a cam check removal tool is available to remove the check assemblies for the 2 1/2 - 6" sizes.