Abstract: 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.

Abstract: A method of controlling a fluid in a life support system including at least one of a G-suit and a counterpressure garment including utilizing a control system comprising a control valve having a moveable part which is moved by an actuator in response to an input to the control system to operate the valve to bring a parameter of the fluid towards a desired value, the input being conditioned to provide a control signal to cause the actuator to move the moveable part of the valve and wherein the method comprises conditioning the input by comparing the input with reference information relating to the position of the moveable part of the valve, and when the comparison indicates that the position of the moveable part of the valve is not at a desired position, issuing the control signal incrementally to move the moveable part and updating the reference information so that the updated reference information is available for future comparison with the input.