1. Cheer up. It is not as difficult as you thought!
Control Valves
Purpose
Terminologies
Construction
Selection criteria
Sizing calculation
Issues on control valve
Cheer up. It is not as difficult as you thought!

2. Introduction Purpose Chemical process applications
to regulate flow of any phase (liquid, gas, fluid and mixed phases) that could pass through it. At the moment, solid phase (such as sand, flour, sugar) is not possible.
Chemical process applications
>80% of final control element found in chem. proc. ind.
Symbols =

3. Construction
Actuator
Body
Plug
Seat

4. Selection Criteria Valve action: ATO vs. ATC compare compare compare
 Air-to-closed (ATC) or Fail open (FO). Use to allow flow of fluid during loss of pneumatic air supply. This action may save overheating of temperature related processes such as catalyst heating or heating of polimerization process.
 Air-to-open (ATO) or Fail closed (FC). Use to prevent flow when no pneumatic air supply. This action may prevent hazardous chemical or flammable fluid from endangering lives.
compare
compare
compare
compare

5. Selection Criteria Valve action: ATO vs. ATC Prevent pressure build-up
The selection of control valve action would depend upon safety of personnel, action time and process hazard upon loss of pneumatic signal.
Prevent pressure build-up
Preventing reaction upstream.
Prevent material from over-heating.
(Smith & Corripio, 3rd. Ed., p.158)

6. Selection Criteria Capacity and sizing P in psi Fluid S.G. Flowrate
In gpm
Example
Calculate the Cv of a control valve when a 12.5 gpm fluid having a SG of 0.8 pass through it. The pressure drop across the control valve is 14 psi.

7. Selection Criteria
Valve characteristics: Linear, equal percentage and quick opening.

8. Selection Criteria
Valve characteristics: Linear, equal percentage and quick opening.
What will be the flowrate when the indicator shows 0.75?
0 gpm
8 gpm
4 gpm
6 gpm
2 gpm
Example
Quick opening
Flow coef. = 0.96
Flowrate = 0.96 x 8 = 7.7 gpm
Linear
Flow coef. = 0.75
Flowrate = 0.75 x 8 = 6 gpm
Equal percentage
Flow coef. = 0.3
Flowrate = 0.3 x 8 = 2.4 gpm

9. Selection Criteria Control valve size selection  
Select an equal percentage control valve for the following condition.
Flow condition
Flowrate, gpm
Pressure drop, psi
Valve lift, %
Maximum
120 10 80
Normal 42 15 50
Minimum 13 20  
Flow condition
Flowrate,
gpm
Pressure
drop, psi
Valve
lift, % Cv
calculated Cv
actual
Maximum
120 10 80
37.9
37.3
Normal 42 15 50
10.8
10.8
Maximum 13 20
2.9
2.93
Contiunue on next page for valve rangeability calculation…

10. Selection Criteria Control valve rangeablity
Check for valve rangeability
Small difference. Selection 2” okay to use.

11. Issues on Control Valves
What make a control valve becomes linear, equal percentage or quick opening control valve?
Why flashing and cavitation are serious problem in control valve?
What causing flashing and cavitation in a control valve?
What is the current solution to flashing and cavitation in control valve?

12. What make a control valve becomes linear, equal percentage or quick opening control valve?
The amount of flow produced with respect to steady increment in stem travel.

13. Why flashing and cavitation are serious problem in control valve?
Erosion

14. What causing flashing and cavitation in a control valve?
Hear sound of cavitation and flashing.

15. What is the current solution to flashing and cavitation in control valve?
Read p.135 of Fisher Control Valve Handbook