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CHAPTER ACTUATORS 9.0 TABLE OF CONTENTS 9.1 INTRODUCTION 1 9.1.1 Linear Motion Actuators 1 9.1.2 Rotary Motion Actuators 2 9.2 ACTUATOR FAILURE MODES 3 9.3 FAILURE RATE MODEL FOR ACTUATOR 4 9.3.1 Base Failure Rate for Actuator 5 9.3.2 Contaminant Multiplying Factor 11 9.3.3 Temperature Multiplying Factor 14 9.4 REFERENCES 18 9.1 INTRODUCTION Actuators provide the means to apply mechanical power to systems when and where it is needed. In general, actuators take energy from pumped fluid and convert it to useful work. This conversion is accomplished by using pumped fluids under pressure to generate a differential pressure across a piston, which results in a force and motion being generated. This chapter identifies the more common failure modes and failure causes of actuators, and develops a procedure for determining the failure rate model of an actuator in its intended operating environment. An actuator typically includes a piston and cylinder, return spring, seals and fluid connectors. Chapter 15 of this Handbook includes procedures for estimating the failure rate of a cylinder. Chapter 4 contains procedures for evaluating spring reliability, Refer to Chapter 3 for seals and Chapter 23 for connectors. Some actuators may include a valve assembly. If so, see Chapter 6. In general, there are two types of output motions generated by actuators: linear and rotary. Within these two classifications there are many different types of actuator assemblies as discussed in the following two sections. 9.1.1 Linear Motion Actuators Linear motion actuators are usually a derivative of one of the following four types: Actuators 9-1 Revision C

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