1. Valve Considerations For Feedwater Applications

2. Presentation Overview Definitions of operating characteristics pertaining to Feedwater control valves Features of the modern Feedwater Control Valve Velocity head considerations in Feedpump Recirc applications and Condensate Recirc Applications Strictly personal and confidential2

3. Hysteresis Defined by ISA 51.1 Hysteresis is the ability to position to the same point for a given instrument signal, regardless of the travel direction. Hysteresis is the result of non-elasticity in mechanical components Strictly personal and confidential3

4. Hysteresis Strictly personal and confidential4

5. Dead Band Time it takes for positioner to vary the output signal to move the valve. Dead band is quantified with signal reversals. Dead band is the result of friction and mechanical connections. Strictly personal and confidential5

6. Combined Effect of Hysteresis and Dead Band Hysteresis may contribute to dead band. Strictly personal and confidential6

7. Features that Influence Hysteresis and DB Friction Stem Packing Balance Seal Compromise may be required to minimize hysteresis and dead band. Actuator Size Seat Leakage Requirement Strictly personal and confidential7

8. Limits of Digital Technology Manufacturer Calculates Resolution Capabilities of the Valve Design: Strictly personal and confidential8

9. Limits of Digital Technology Resolution or Accuracy is Additive: 1.Add positioner accuracy to valve accuracy for system capability. 2.Digital systems (QT, FT, DVC, SVI) do not lower valve resolution. 3.The only way to negate calculated resolution is through Electro-hydraulic or Motor Operator Strictly personal and confidential9

10. Performance Comparison Comparison FactorPremium Digital Conventional Pneumatics Hydraulics Reduced maintenanceYesNo ReliabilitySuperiorHighLow Fire HazardNo Yes Simple calibration and tuning YesNo Lower lifecycle costsYes No Hysteresis and deadband< 0.5%< 1 – 3%< 0.3% Dead time on seat< 150 msec< 300 to 1000 msec < 100 msec Resolution and deadband< 0.25%< 0.5 – 1.5%< 0.1%

11. Interpretation of Results “Boots” shown at both ends Indicates loose position feedback mechanism Common condition with Scotch Yoke type positioner linkages. Example: Strictly personal and confidential11

12. Causes of Excessive Dead Band Digital Positioner Setup –Positioner not configured for Scotch Yoke linkage –Positioner not configured for spring return piston –Tuning parameters depend upon system setup –Sloppy linkage Strictly personal and confidential12

13. Linkage Improvement Cam Style Motion Converter Minimizes hysteresis in the system Strictly personal and confidential13

14. Features of Modern Feedwater Valves Rangeability Equal Percentage Single valve for Start Up and Main Strictly personal and confidential14

15. Features of Modern Feedwater Valves Accurate Position Feedback Strictly personal and confidential15

16. Features of Modern Feedwater Valves Digital Positioner Technology Strictly personal and confidential16

17. Standards vs. Guidelines, Steam  ISA 75 has recommendations.

18. Multi Stage Letdown Multi-stage Pressure Drop Eliminates Cavitation

19. Trim Analysis, Liquid Applications Graphical representation of Pressure Recovery Factor Page 19

20. Trim Analysis, Cavitation Prediction Methods Page 20

21. Definition of Sigma Page 21

22. How is Sigma Determined? Manufacturer Determines Sigma by Test –Application Experience –Cavitation Damage Testing of Aluminum Trims Varies according to –Style –Size –Capacity –Application Pressure Established by: –10% Increments of lift –Two valve sizes of like geometry –Two upstream pressures to determine scaling factors Page 22 Sigma-  Vibration  mv cc ii  mr 1.020+

23. Seat Protection Features, Min Flow / Recirc Snap Acting Relay Function Pneumatic Digital Strictly personal and confidential23 PLUG CAGE SEAT RING BODY

24. Material Considerations for High Vel. Apps Angle Valve Carbon Steel Valve Body (A216-WCB,WCC) Globe Valve Chromoly (A216-WC6 Casting, F11 Forging) High Chrome for Fossil (A216-C5, F5 Forging) Strictly personal and confidential24

25. Summary Valve design will limit digital positioner performance. Critical valve positioners require modern linkages –Cam plate type linkage –Computer compensation of four bar linkage –Elimination of Scotch Yoke type positioner linkage Cavitation index warnings should be evaluated on a case by case basis Strictly personal and confidential25