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A device to engage and disengage the valve stem from an electric motor or handwheel
Declutch lever
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Refers to the overshoot and undershoot that occur as the receiving device tries to match the sending device
Hunting
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A valve actuator that uses a piston to translate a signal into valve motion
Hydraulic actuator
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A mechanical device attached to the valve stem to indicate valve position by way of remote and/or local indicating lights
Limit switch
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An instrument transformer that provides accurate position indication throughout the range of a component’s travel
Linear variable differential transformer (LVDT)
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A handwheel or lever that directly controls valve stem position
Mechanical actuator
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A valve actuator that use pneumatic (air, nitrogen, etc.) pressure as the source of thrust to operate the valve stem
Pneumatic actuator
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Switches constructed of flexible ferrous strips and are placed near the intended travel of the valve stem or control rod extension
Reed switches
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A remote indication or control system. Consists of synchro units that electrically govern or follow the position of a mechanical indicator or device
Synchro equipment
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A type of electrical valve actuator. The valve stem is attached to a magnetic core that is attracted by a magnetic force generated by a coil when energized
Solenoid valve
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A device used to manipulate the position of the valve stem
Valve Actuator
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DESCRIBE the four basic types of pneumatic actuators.
Pneumatic actuators use air pressure on either one or both sides of a diaphragm or piston to provide the force to position the valve
- Pneumatic diaphragm
- Pneumatic piston
- Pneumatic cylinder
- Pneumatic vane
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Given a drawing, DESCRIBE how a pneumatic-operated valve with a solenoid pilot valve would reposition following a loss of pneumatics
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Given a drawing, DESCRIBE how a pneumatic-operated valve with a solenoid pilot valve would reposition following a loss of electrical power
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STATE the methods that can be used to determine or verify valve position locally or remotely
- The simplest means of determining valve position is observing the position indicating light
- Another method to determine valve position is by locally observing valve stem position
- An additional method to determine valve position is by a locally mounted pointer
- Some valves do not have any visual means to determine valve position. In these cases, system parameters such as flow, pressure, and temperature can be used, as well as attempting to operate the valve in the closed direction
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DESCRIBE the proper methods or techniques for operating and verifying the position of manual valves
To physically check a valve position, turn the valve handwheel a short distance in the “shut” direction. If the handwheel turns, the valve is open. If the valve handwheel will not turn, the valve is already shut
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DESCRIBE the synchro position indicators to include the basic construction and theory of operation
Remote indication or control may be obtained by the use of self-synchronizing motors, called synchro equipment. Synchro equipment consists of synchro units that electrically govern or follow the position of a mechanical indicator or device. An electrical synchro has two distinct advantages over mechanical indicators: (1) greater accuracy, and (2) simpler routing of remote indication.
- There are five basic types of synchros that are designated according to their function. The basic types are:
- Transmitters
- Differential transmitters
- Receivers
- Differential receivers
- Control transformers
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DESCRIBE limit switches and reed switches to include basic construction and theory of operation
- A limit switch is a mechanical device that can be used to determine the physical position of equipment
- Reed switches are more reliable than limit switches, due to their simplified construction
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DESCRIBE potentiometer position indicators to include basic construction and theory of operation
Potentiometer valve position indicators provide an accurate indication of position throughout the travel of a valve or control rod. The valve stem extension is physically attached to a variable resistor, usually through a geared linkage
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