The end cap (number 9 in Figures 11 and 2) is either a cylindrical or square item. The cylindrical version screws onto the output end of the high pressure cylinder. The square type is held in place with tie rods and bolts. The end cap has a hole in the center for the check valve and outlet body. It will also have a connection point for the incoming fresh water. The water flows through holes machined through the cap to line up with inlet holes in the check valve.