1. Flow characteristics selection
1.1. Recommendations:
1.2. Equal percentage
1.2.1. When the major portion of the control-system pressure drop is not through the valve
1.2.2. For temperature- and pressure-control loops
1.3. Linear
1.3.1. In liquid-level or flow-control service
1.3.2. Where the pressure drop across the valve is expected to remain fairly constant
1.3.3. Where the major portion of the control system’s pressure drop is through the valve
1.4. Quick-opening
1.4.1. For frequent on/off service, or where an “instantly” large flow is required, i.e.
2. Rules of thumb for sizing and selection
2.1. Guidelines
2.1.1. The pressure drop allocated to the control valve should be equal to 33% of the dynamic losses in the system at the rated flow
2.1.2. Pressure drop allocated to a control valve in the suction or discharge line of a centrifugal compressor should be 5% of the absolute suction pressure
2.1.3. In a system where static pressure moves liquid from one pressure vessel to another, the pressure drop allocated to the valve should be 10%
2.1.4. Pressure drops in valves in steam lines to turbines, reboilers and process vessels should be 10% of the design absolute pressure of the steam system
2.1.5. The gain on a control valve should never be less than 0.5
2.1.6. Avoid using the lower 10% and upper 20% of the valve stroke
2.1.7. Control-valve bodies are one size less than the line size
3. Materials of construction
3.1. Specific materials for
3.1.1. Hard body
3.1.1.1. Must
3.1.1.1.1. Match the material of the interconnecting piping
3.1.2. Trim
3.1.3. Soft gasket
3.1.4. Seal
3.1.5. Packing
3.1.5.1. Needs to
3.1.5.1.1. Withstand high pressure
3.2. Miscellaneous
3.2.1. Customer preferences
3.2.2. Cost considerations
3.2.3. Nature of the fluid
3.2.4. Considerations for high- and low temperature services
4. Maintenance
4.1. Common problems on
4.1.1. Wear of the valve body
4.1.2. Actuator diaphragm
4.1.3. Seat
4.1.4. Packing
5. Control valve
5.1. Valve characteristics
5.1.1. Operate over a wide range of flows
5.1.2. Responde to any signal across its operatimg range
5.1.3. React to incremental adjusmets from the controller
5.1.4. Respond with the required speed
5.2. Depends
5.2.1. Quality of its actuator
5.2.2. Positioner
5.2.2.1. Added to
5.2.2.1.1. Amplify the controller's signal
5.3. Most important
5.3.1. Gain
5.3.1.1. Depends
5.3.1.1.1. Valve characteristics
5.3.1.1.2. Process conditions
6. Desing parameters
6.1. State
6.2. Vapor pressure
6.3. Flow rate
6.4. Inlet and oulet pressures
6.5. Inlet temperature
6.6. Viscosity
6.7. Heat radio
6.8. Density
6.9. Molecular weight
7. Flow coefficient (Cv)
7.1. Most important valve parameter
7.1.1. Depends
7.1.1.1. Flow is compressible
7.1.1.2. Flow is incompressible
7.1.1.3. Flow is mixed-phase
8. Trim and bonnet
8.1. Trim
8.1.1. Internal parts of the valve that are in contact with the fluid
8.1.1.1. Relationship
8.1.1.1.1. Flow capacity
8.1.1.1.2. Valve plug-fit
8.1.1.1.3. Proper shut-off of the valve
8.2. Bonnet
8.2.1. Designed to meet certain temperature range
9. Noise
9.1. Generate by control valve
9.1.1. Due to
9.1.1.1. Mechanical vibration
9.1.1.1.1. High velocities
9.1.1.1.2. Pressure oscillations
9.1.1.1.3. Unsteady flow
9.1.1.2. Cavitation
9.1.1.2.1. Depends
9.1.1.3. Aerodynamic effects
9.1.1.3.1. Results from
9.1.1.3.2. Most common and worst source of noise
10. Selecting the type of valve
10.1. By flow capacities
10.1.1. Expressed in terms of Cv. You can see this terms in the link of this bubble
10.1.1.1. Then
10.1.1.1.1. Once a valve type and flow characteristic are established, a preliminary size can be determined by computing the valve stroke for each design flow case
10.1.1.1.2. Choosea valve that can operate between 10–80% of the valve stroke across the expected range of operation