Control Valves PDF

Types of control valve Gate Valves Best Suited Control: Quick Opening Recommended Uses: 1. Fully open/closed, non-throttling 2. Infrequent operation 3. Minimal f luid trapping in line Applications: Oil, gas, air, slurries, heavy liquids, steam, noncondensing gases, and corrosive liquids Advantages:...

Types of control valve Gate Valves Best Suited Control: Quick Opening Recommended Uses: 1. Fully open/closed, non-throttling 2. Infrequent operation 3. Minimal f luid trapping in line Applications: Oil, gas, air, slurries, heavy liquids, steam, noncondensing gases, and corrosive liquids Advantages: Disadvantages: 1. High capacity 1. Poor control 2. Tight shutoff 2. Cavitate at low pressure drops 3. Low cost 3. Cannot be used for throttling Types of control valve Globe Valves Best Suited Control: Linear and Equal percentage Recommended Uses: 1. Throttling service/f low regulation 2. Frequent operation Applications: Liquids, vapors, gases, corrosive substances, slurries Advantages: Disadvantages: 1. Efficient throttling 1. High pressure drop 2. Accurate f low control 2. More expensive than other valves 3. Available in multiple ports Types of control valve Ball Valves Best Suited Control: Quick opening, linear Recommended Uses: 1. Fully open/closed, limited-throttling 2. Higher temperature f luids Valve Ball Applications: Most liquids, high temperatures, slurries Advantages: Disadvantages: Valve Body 1. Low cost 1. Poor throttling characteristics 2. High capacity. 2. Prone to cavitation 3. Low leakage and maintenance. 4. Tight sealing with low torque Types of control valve Butterfly Valves Best Suited Control: Linear, Equal percentage Butterfly Recommended Uses: 1. Fully open/closed or throttling services 2. Frequent operation Valve Body 3. Minimal f luid trapping in line Applications: Liquids, gases, slurries, liquids with suspended solids Advantages: Disadvantages: 1. Low cost and maintenance. 1. High torque required for control 2. High capacity 2. Prone to cavitation at lower f lows 3. Good f low control 4. Low pressure drop Butterfly Valve for Control Actuator Valve Body Butterfly Check Valves Check valves allows flow in only one direction Two most common designs are the swing check and the lift check Swing check; the disk swings around a pivot point when the flow goes in one direction. When the flow reverses the valve closes In a lift check the flow will lift the disk upwards and when the flow reverses will push the disk closed  Check valve Swing Check Lift Check Disk Pivot Direction of Flow There are many types of valves available, each having their advantages and limitations. The basic requirements and selection depend on their ability to perform specific functions such as: 1. Ability to throttle or control the rate of flow; 2. Lack of turbulence or resistance to flow when fully open - turbulence reduces head pressure; 3. Quick opening and closing mechanism - rapid response is many times needed in an emergency or for safety; 4. Tight shut off - prevents leaks against high pressure; 5. Ability to allow flow in one direction only - prevents return; 6. Opening at a pre-set pressure - procedure control to prevent equipment damage; and 7. Ability to handle abrasive fluids - hardened material prevents rapid wear. Term Part of the Process Identify the Mode that the Controller must be in Master Controller Slave Controller Process Variable Manipulated Variable The Load Where will the operator input the Setpoint?