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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.

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 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.

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.

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.