Arca Regler GmbH has invented a hermetic stem-seal designed for control and shutoff valves. The key part of the Optiseal® stem sealing is the hydraulic supported double ring diaphragm. This hydraulic support takes over all forces resulting from static pressure from the diaphragm. Compared with a bellows seal, Optiseal ® offers sterilisation capability and resistance against polymerisation. Diaphragm rupture can be indicated by controlling the pressure between both diaphragms; however the safety and function of the stem seal is not affected even if one layer of the diaphragm is ruptured.