Design and Characterization of a Rotary Actuated Hot Gas Servovalve

This paper describes the design and characterization of a unique three-way hot gas servovalve designed for the flow control of steam at 235°C. The valve incorporates a pressure-balanced rotary spool coupled to a servomotor/gearbox/encoder combination to achieve high-bandwidth and high-precision operation, and also incorporates several design elements in order to accommodate the high temperatures associated with the working fluid. The spool and sleeve entail geometries of low aspect ratio and are mechanically isolated from the manifold with Viton O-rings to ensure uniform thermal expansion and contraction. To thermally isolate the DC motor, a PEEK motor mount is used to connect the motor housing with the valve manifold. Additionally, the motor shaft is coupled to the spool with an Oldham coupling that incorporates a PEEK center disk to further insulate the motor from the high temperature spool. The desing is presented, along with experimental data that characterizes the dynamic performance and flow characteristics of the valve.