Valve stepper motor and tranmission

摘要

A valve assembly includes an actuator and a valve. The valve includes a valve body (60) having first (61) and second (62) ports and a valve seat (64) between the first and second ports (61, 62). A valve member (65) is carried on a valve stem (68) and the valve stem (68) is moveable to move the valve member (65) at least one of into or out of engagement with the valve seat (64) to prevent or permit communication between the first and second ports (61, 62). The actuator includes a stepper motor the rotational movement of which is converted to linear movement of the valve stem (68) by a transmission means. The transmission means is adapted to maintain the valve stem (68) in a position to which it is moved by the operation of the actuator whereby the transmission means is a non back-driveable transmission.