Instrumentation : Selection of valve

Field Instrumentation Valves
1

SELECTING A VALVE TYPE

Can classify the valve according to Stroke / Valve travel

  1. Equal Percentage: equal increments of valve travel produce an equal percentage in flow change

  2. Linear: valve flow is directly proportional to the valve stoke

  3. Quick opening: large increase in flow with a small change in valve stroke

  4. Equal Percentage (most commonly used valve control) a. Used in processes where large changes in pressure drop are expected b. Used in processes where a small percentage of the total pressure drop is permitted by the valve c. Used in temperature and pressure control loops

  5. Linear a. Used in liquid level or flow loops b. Used in systems where the pressure drop across the valve is expected to remain fairly constant (ie. steady state systems)

  6. Quick Opening a. Used for frequent on-off service b. Used for processes where “instantly” large flow is needed (ie. safety systems or cooling water systems)

2

Architecture of Control valve based on operation

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