The Cat Pumps 541060 is a check valve for the 7500, 7500s, and 7600s unloaders and unloaders integrated with 2SF, 2SFX, 3DX, and 3DNX series pressure washer pumps. It is made with brass to resist corrosion. An O-ring is included with this check valve. This is an official OEM part made by CAT Pumps.