The force on top of the diaphragm, which opposes the control pressure, is due to the air charge in the element. Identify the graphic symbols for various types of pressure-control valves Hydraulic Valve Division Elyria, Ohio, USA Catalog MSG/US Pressure Control Valves General Description Series R4V*5 and R6V*5 pressure relief valves feature a manual adjustment pilot stage which controls a seated type main stage. These two forces are the operating forces of the OROA valve that control the main por