Suttner ST-291 Pressure Regulation Unloader Valves. The Suttner ST-291 Unloader Valve is equipped with a thread for fixing it at the frame of your high pressure cleaner. According to in-house statements the switch with protection class IP 67 which is used for this valve is "as water-proof as a submarine". Unlike the other valves the switch does not come into contact with water or other mediums as it is mounted on the outside of the valve and mechanically operated by the piston rod. It is of the directional contact type i.e. that a contact is produced in any position.