Actuated valves manufactured by Audco India Ltd and marketed by Larsen & Toubro Ltd are operated either electrically, pneumatically or hydraulically. The electrically actuated valves are commonly called Motor Operated Valves (MOVs). MOVs find large-scale application in process plants, power plants, refineries, petroleum tank farms, cross-country pipelines, etc. Electrical actuators are mostly multi-turn, but are also available with quarter-turn output. Electrical actuators are available with a wide variety of accessories. Some of the commonly used ones are: (l) Position or Travel Limit Switches. These give feedback about the status of valve operation – as to whether the valve is fully open, fully closed or at an intermediate position. The feedback could also be used to trigger operation of connected instruments. Actuator motors should be switched off when the valve reaches the fully open or fully closed positions to prevent overheating and damage. This is achieved with the help of limit switches. Position limit switches are used in position-seated valves like parallel-slide gate valve, plug, ball & butterfly valves. (2) Torque Limit Switches. If the valve becomes jammed during operation, the electric motor will continue to run, resulting in damage. Torque limit switches cut off power to the motor when a pre-set torque is reached and protect the motor. (3) Continuous Position Indicator/Transmitter. These provide continuous indication about valve travel and position (by indicators showing “Open,” “Intermediate” or “Close”) (4) Thermostat, which protects the motor from over-heating and burning out, by cutting off power once a set temperature is exceeded.
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