Abstract: A hermetically sealed valve has a magnetically actuated rolling diaphragm valve mechanism, and providing an in-line variable opening valve that is completely sealed and requires no shaft, bushings or moving components through the valve body. This provides a valve with a generally in-line flow, which may be completely isolated from contaminants or from the outside environment. The magnetic actuating mechanism permits precise gradual positional control of the valve and at the same time provides considerably greater actuation force against differential pressure across the valve than has previously been possible. The valve actuation mechanism is readily adaptable to digital control techniques.