Abstract: The pneumatic motor of an air hoist has a blow-off valve in its supply passage. When the blow-off valve is open to the atmosphere, the air pressure at the inlet of the motor is substantially reduced. The blow-off valve is held closed by a piston having a piston surface in an air chamber. The air chamber is supplied with compressed air through a restriction. The hoist has a hook by which it can be suspended and the hook is clamped to the housing of the hoist by means of a pre-loaded Belleville-spring. When the spring yields due to overload, a vent valve will open and vent said air chamber. As a result, the blow-off valve suddenly opens to limit the torque of the motor.