This SAE Aerospace Recommended Practice (ARP) provides definitions and background information for understanding the physical performance, and test procedures of electrohydraulic flow control servovalves. The recommendations are confined to interface definition and input/output characteristics. This ARP does not restrict or attempt to define the internal characteristics of servovalves. As such, the recommendations are equally applicable to valves having different internal functioning, different ratings, different physical size, and valves used with different fluids. In certain instances, standards for valve design are recommended for the purpose of interchangeability, as for example, valve polarity, mounting bolt and fluid port locations. The ARP provides extensive guidance for the preparation of Procurement Specifications and for functional testing. A sample Procurement Specification is provided in Appendix A. The primary focus of this ARP is on four-way valves. Three-way valves are discussed to a limited extent and terminology for pressure control valves is presented in Appendix B. This ARP is applicable to fluid power systems in all types of flight vehicles, and it is applicable to Military, Civil and Space design/certification standards. Additional specifications or specialized test procedures may be necessary to define special requirements for specific control systems, and such considerations are beyond the scope of this ARP.
Rationale: The document has been revised to clarify definition of terms and align them with the illustrations given in figures, update document references, and correct multiple typographical errors introduced during previous revisions.