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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.

Various gas systems are classified in a broad sense, component operation is described in moderate detail, pertinent design parameters are discussed, and possible modes for system operation are listed.

Gas, for the purpose of this ARP, shall be defined as the gaseous product(s) resulting from the decomposition, dissociation, or combustion of liquid or solid mono or bi-propellants. Where other gases such as heated N2, H2, H2O (steam), etc., which may have similar physical and/or chemical properties as the defined "gas", are used to effect testing economics, they may he considered as being included in this ARP.

Various gas systems are classified in a broad sense, component operation is described in moderate detail, pertinent design parameters are discussed, and possible modes for system operation are listed.

Gas, for the purpose of this ARP, shall be defined as the gaseous product(s) resulting from the decomposition, dissociation, or combustion of liquid, or solid mono or bi-propellants. Where other gases such as heated N2, H2, H2O (steam), etc., which may have similar physical and/or chemical properties as the defined "gas", are used to effect testing economies, they may be considered as being included in this ARP.

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.

The recommendations contained herein are confined to the input and output characteristics of electrohydraulic mechanical feedback servoactuators. The information presented should be useful for standardizing the terminology and for specification of physical and performance parameters. The recommendations do not restrict nor attempt to define the internal design characteristics of servoactuators. As such, the material is equally applicable to servoactuators having different internal functioning, different ratings, different physical size, etc. In certain instances, standards for actuator design are recommended to increase interchangeability as, for example, pigtail color-coding and actuator polarity. The specifications contained herein should be adequate to describe electrohydraulic mechanical feedback servoactuators used for position control. Additional specifications may be necessary to define special requirements for specific control systems.

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.

The recommendations contained herein are confined to the input and output characteristics of electrohydraulic mechanical feedback servoactuators. The information presented should be useful for standardizing the terminology and for specification of physical and performance parameters. The recommendations do not restrict nor attempt to define the internal design characteristics of servoactuators. As such, the material is equally applicable to servoactuators having different internal functioning, different ratings, different physical size, etc. In certain instances, standards for actuator design are recommended to increase interchangeability as, for example, pigtail color-coding and actuator polarity. The specifications contained herein should be adequate to describe electrohydraulic mechanical feedback servoactuators used for position control. Additional specifications may be necessary to define special requirements for specific control systems.

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.

In this document a servovalve is defined only as a valve, normally used in a servomechanism which has a hydraulic output (flow, pressure) which is a function of an electrical input (voltage, current, differential current). This ARP will confine itself to describing those parameters which are peculiar to such valves.

The recommendations contained in this ARP are primarily confined to the input and output characteristics of Direct Drive Servovalves (DDV). The only exception to this approach involves the definition and specification of chip shear force, which is not typically measurable by nondestructive external testing. 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. Direct drive servovalves are of two basic types; open loop and closed loop. In the case of open loop direct drive servovalves, the significant input is the motor current as is the case with electrohydraulic servovalves covered in ARP490. Closed loop direct drive servovalves include a means of position feedback and rely on an electronic controller to control its performance characteristics.

This specification establishes general design, performance, and test requirements for hydraulically powered servoactuators when used in aircraft flight control systems.