Two-position, spring return motors used to operate dampers and valves. Used to operate dampers and valves in applications where it is necessary or desirable to have the controlled element return to the starting position in the event of power failure or interruption. Replace M445A,D; M845A,C,E; and M865B motors. Available with factory-installed transformers, or an internal transformer can be added in the field. Oil-immersed motor and gear train provide reliable performance and long life. Provide NEMA 3 weather protection with wiring box, when mounted upright. Electrically normally closed (at closed position when control signal is at minimum level) and rotate clockwise to open with a signal increase. Integral helical spring that returns the motor shaft to the normal position (fully closed for M4185 and M8185; fully open for M4186) on power interruption. Internal actuator motor and circuitry operate from 24 Vac. Line voltage models shipped with internal transformers. Double-ended, 3/8 in. (10 mm) square crankshaft