An actuator base, bobbin, and pole piece form a pocket for an armature that a flexible membrane encloses to form an armature chamber filled with an incompressible fluid. The membrane protects the armature from exposure to corrosive fluids flowing in a conduit. Conduit flow can be stopped by driving the membrane against a valve seat. Pressure from the controlled fluid in the conduit is transmitted through the membrane to the fluid within the armature chamber so that the armature does not need to counteract force applied to the membrane by the conduit fluid's pressure.