Abstract: A shut-off system for a filling/dispensing valve of a compressed gas cylinder includes an electric motor that rotates the valve stem through a clutch. The clutch operatively couples the motor to the stem to allow the stem to be either motor-turned or manually-turned only in the valve-closing direction, and selectively decouples the motor from the stem to allow manual rotation of the stem in either direction. An actuation signal is fed to a microprocessor to turn the motor on in response to a predetermined condition. During motor operation, a voltage sensor generates a control signal having a value indicative of the voltage across the switch, which value is inputted to the microprocessor. The microprocessor has a stored value representing the resistance across the closed switch, and it thus can compute the instantaneous value of the current drawn by the motor, which is periodically compared with a stored maximum current value.