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This recommended practice is intended as a guide for the specification of electrohydraulic mechanical feedback servoactuators used for position control. It provides performance definitions and capabilities that are specific to mechanical-feedback servoactuators and different from those applicable to electrical-feedback servoactuators.

This specification establishes the requirements for power operated hydraulic servoactuators when used in flight control systems. These servoactuators may be controlled by mechanical, hydraulic or electrical inputs or combinations thereof, and may be powered by one or more hydraulic systems. The complete servoactuator package may incorporate primary components such as control servovalve, input linkage and position feedback lever in addition to the actuating cylinder. Secondary components may also be included such as stability and control augmentation actuators, bypass valves, residual pressure compensators, electrohydraulic servovalves, filters, pressure switches, motor or solenoid operated shut-off valves, thermostatic control valves, hydraulic logic, mechanical locking devices and electrical transducers.

The recommendations contained in this ARP are confined to the input and output characteristics of electrohydraulic flow-control servovalves. The information presented should be useful in standardizing the terminology, the specification of physical and performance parameters, and the test procedures used in conjunction with these components. The recommendations do not restrict nor attempt to define the internal design characteristics of servovalves. As such, the material is equally applicable to servovalves having different internal functioning, different ratings, different physical size, etc. In certain instances, standards for valve design are recommended to increase component interchangeability, as, for example, pigtail color-coding, valve polarity, mounting bolt and fluid port locations. The specifications contained herein should be adequate to describe electrohydraulic flow-control servovalves.

The recommendations contained in this ARP are confined to the input and output characteristics of electrohydraulic flow-control servovalves. The information presented should be useful in standardizing the. terminology, the specification of physical and performance parameters, and the test procedures used in conjunction with these components. The recommendations do not restrict nor attempt to define the internal design characteristics of servovalves. As such, the material is equally applicable to servovalves having different internal functioning, different ratings, different physical size, etc. In certain instances, standards for valve design are recommended to increase component interchangeability, as, for example, pigtail color-coding, valve polarity, mounting bolt and fluid port locations. The specifications contained herein should be adequate to describe electrohydraulic flow-control servovalves.

The recommendations contained in this recommended practice are confined to the input and output characteristics of electrohydraulic flow-control servovalves. The information presented should be useful in standardizing the terminology, the specification of physical and performance parameters, and the test procedures used in conjunction with these components. The recommendations do not restrict nor attempt to define the internal design characteristics of servovalves. As such, the material is equally applicable to servovalves having different internal functioning, different ratings, different physical size, etc. In certain instances, standards for valve design are recommended to increase component interchangeability, as, for example, pigtail color-coding, valve polarity, mounting bolt and fluid port locations. The specifications contained herein should be adequate to describe electrohydraulic flow-control servovalves.

This SAE Aerospace Recommended Practice (ARP) provides definitions and background information regarding the physical performance and testing of electrohydraulic flow control and pressure control servovalves. This ARP also provides extensive guidance for the preparation of procurement specifications and for functional testing. NOTE: An example of a procurement specification is provided as Appendix A.