Askalon Fail Safe Electric Lock‐in‐last position unit
Pneumatic actuators can have three fail positions if air supply fails. Positions are fail close, fail stay or fail open. For spring return diaphragm actuators fail close and open are spring forced. Fail lock is performed by switch valve Fisher 167DA. Double action piston actuators have fail positions using Fisher 377 Trip Valve relay. Fail close and open must have air bottle.
Askalon has developed an electric fail stay unit that can be used both for diaphragm and piston actuators. Fail stay kit uses a signal trip relay and a solenoid valve. Locking time is about same as positioner dead band time. Max. ambient temperature 60°C.