Cashco 988-MB - Manual (Page 17)

17 IOM-988/989-BODY
4. Valve exhibits “excess” seat leakage.
Possible Cause Remedy
D. Excess wear. D1.
D2.
D3.
D4.
D5.
Oversized valve operating too close to seat; go to reduced
trim.
Incorporate stellite trim.
Remove particulate.
Possible excess cavitation in liquid service. Change operation
parameters.
Re-lap plug–seat surface.
E. Misalignment. E. Realign body–stem–actuator.
F. Composition seat failure. F1.
F2. Replace soft seat.
Remove “dirty” portion of fl uid causing failure.
G. Seat ring gasket failure. G. Replace seat ring gasket.
5. Premature packing leakage.
Possible Cause Remedy
A. Over-temperature. A1.
A2.
A3.
Bring process temperature to 450°F (232°C) or less.
Remove insulation along bonnet; allow direct contact with ambi-
ent air.
Replace standard packing with high-temp. packing.
B. Misalignment. B. Realign body–stem–actuator.
C. Wear. C1.
C2. Remove dirt/grit from fl uid.
Reduce cyclic travel.
D. Improper design for applied service. D. Install alternate packing design.
E. Corrosion of stem. E1.
E2. Use alternate stem material.
Incorporate leak-off option.
F. Insuffi cient spring force. F1.
F2. Replace packing spring.
Add one packing ring.
6. Bonnet gasket leaking.
Possible Cause Remedy
A. Improper bonnet bolting draw down. A. Replace gasket and draw down bolting evenly in a cross-pattern.
B. Corrosion. B. Alternate gasket material and/or alternate body/bonnet material.
C. Warped bonnet and/or body fl ange. C. Replace body and/or bonnet and bonnet gasket. Draw down
bonnet bolting evenly in a cross-pattern.
7. Body fl ange leakage.
Possible Cause Remedy
A. Over-tightening fl ange bolting. A1.
A2. Loosen bolting, replace gasket, reinstall new fl ange bolting.
Replace warped fl anges.
B. Corrosion of split rings. B. Replace CS split rings with SST split rings.
C. Improper pipe supports and anchors. C. Provide piping anchors and guides at control valve station.
Restrain bending movements.