The KVS/ETS valves operate modulating by electronically controlled activation of the AST stepper motor. The motor is a type 2-phase bi-polar, which stays in position unless power pulses from a driver initiate the two discrete sets of motor stator windings for rotation in either directions. The motor is operating the spindle, where rotating movements are transformed into linear motion by the transmission in the cage cone assembly. The AST motor housing as a standard has a glass sealed M12 connection. It can be connected with customized cable and plug/socket combinations.