A torque motor valve actuator for use with a valve assembly is provided. The torque motor valve actuator includes an armature spring having a first end portion, a second end portion and a rigid central portion. The first end portion and the second end portion are coupled to the rigid central portion by a respective flexible portion, and the rigid central portion defines a bore that extends along a first axis. The torque motor valve actuator includes an armature having a first end and a second end. The armature extends along a longitudinal axis that is substantially parallel to the first axis of the bore, and the armature is coupled to the bore of the armature spring between the first end and the second end.

A pressure relief device for a double isolation valve comprises a body with a valve cavity. The valve body has a pocket formed therein. A disc is disposed in the central section of the pocket. The disc is interposed between two spring-actuated seats. Each of the seats is in fluid communication with opposing valve sides. The pocket central section is in fluid communication with the valve body cavity. Each of the seats is provided with two different types of gaskets in series. In operation, reverse pressure causes retraction of the seats, thereby relieving valve body cavity overpressure.

A method of detecting failure of a two-stage servo-valve in which the power-controlling movable member is connected to the rotor of a torque motor of a pilot stage by mechanical feedback. A malfunction signal is generated in response to detecting that the rotor of the torque motor has engaged a stop. The invention also provides a servo-valve for implementing such a method.