| 摘要 |
A valve assembly including an actuator and a valve, the valve including a valve body having first and second ports and a valve seat between the first and second ports, a valve member carried on a valve stem and the valve stem being moveable to move the valve member at least one of into or out of engagement with the valve seat to prevent or permit communication between the first and second ports and wherein the actuator includes a stepper motor the rotational movement of which is converted to linear movement of the valve stem by a transmission, the transmission being adapted to maintain the valve stem in a position to which it is moved by the operation of the actuator whereby the transmission means is a non back-derivable transmission.
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