I will add this suggestion. Apparently Jason's machine shop turned down a relief in the top portion of some of his check valves for the diesel lines. Keep in mind that they have a rubber seal, not a crush washer. They do not require that much torque, and if you're not careful the head of the check valve will pop off! I broke one with a 5" long wrench handle! Once you get them snug to where they require effort to turn with the wrench, I wouldn't go any further than 1/8th of a turn.