For opening or closing circuit at a set point within the adjusting range, operated by increasing or decreasing pressure. There are models actuated by diaphragm, piston, etc. The most common models are described below for your reference. Please ask for further information and brochures of various manufacturers and models available from local suppliers when required. Piston Actuated, Switching pressure difference not adjustable. Setting of switching point by screw with hex. recessed hole protected by plastic cover.