Bosch Rexroth Hydraulics R901102362, HED 8 OH-2X/200K14S. Hydro-electric piston type pressure switches. Hydro-electric pressure switches of model HED 8 are piston-type pressure switches used to monitor a pressure value in a circuit. As a pressure value is achieved (rising or falling), the HED micro-switch changes state, which can be used as an indicator for the next sequential operation or shutdown. The HED microswitch is not a current carrying device; it is an actuator/sensor.