Apparatus and method for controlling fluid flow

An actuator base (16), bobbin (14), and pole piece (24) form a pocket for an armature (30) that a flexible membrane (40) encloses to form an armature chamber filled with an incompressible fluid. The membrane (40) protects the armature (30) from exposure to corrosive fluids flowing in a conduit (44). Conduit flow can be stopped by driving the membrane (40) against a valve seat (54). Pressure from the controlled fluid in the conduit (40) 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 (40) by the conduit fluid's pressure.