Cashco SCV-S - Manual (Page 10)

IOM-SCV-S 10
5. Inadequate valve shutoff.
Possible Cause Remedy
A. Permanent "tracks" where seating occurs. A1. Relap body seat and plug (metal seat).
A2. Replace body and plug or comp. seat disc.
B. Excess valve pressure drop. B. Reduce valve's shutoff pressure drop.
C. Insuffi cient IAS pressure. C. Provide required level of IAS pressure.
D. Obstruction at seat. D. Remove body and inspect for obstruction.
E. Improper calibration. E. Recalibrate positioner and valve stroke.
F. Improper actuator bench set range. F. Disassemble actuator and change to stiffer range springs.
Reinstall and increase IAS to proper level.
1. Unit can not pass enough fl ow.
Possible Cause Remedy
A. Sizing data not correct; valve undersized. A1. Check actual pressures, temperature, and fl ow rates against
the variables used for sizing.
Recalculate Cv Required.
A2. Replace unit with larger body size.
B. Obstruction at inlet. B. Remove valve and inspect line for blockage.
C. Insuffi cient valve travel. C1. Verify full travel.
C2. Verify correct IAS pressure.
2. Unit can not control steadily at low fl ow rates.
Possible Cause Remedy
A. Sizing data not correct; valve oversized. A1. Check actual pressures, temperature and fl ow rates against
the variables used.
A2. Replace full port body with reduced port body.
B. Obstruction at inlet. B. Remove valve from line and inspect for something
causing blockage.
C. Too short of “stroke”. C. Remove unit and calibrate.
D. Excess pressure drop. D1. Check actuator bench setting; re-calibrate as required.
D2. Check design pressures against actual pressures. Replace
“low” bench set range springs with higher bench set
range springs.
E. Insuffi cient IAS pressure. E. Provide required level of IAS pressure.
F. Incorrect fl ow direction. F. Verify fl ow with arrow cast on body; FTO
3. Valve body leaking at clamped end connection joints.
Possible Cause Remedy
A. Excess pressure levels. A. Check actual pressures against those indicated in Technical
Bulletin. Reduce pressures as necessary.
B. Loose clamp. B. Remove valve from service. Disassemble and clean.
Reassemble and properly tighten all clamps at reinstallation.
C. Excessive piping stress. C. Place hanger on control valve unit.
D. Improper pipe alignment. D. Re-do piping properly.
4. Fluid leakage at bonnet or at upper stem seal ring.
Possible Cause Remedy
A. Gasket failure. A1. Remove body, disassemble, remove old gasket Install new
gasket,new stem seals, reassemble and reinstall.
A2. Seal ring failure.
B. Overheating B. Ensure that max. operating temperature of
366°F (186°C) is not exceeded.)
C. Stem seal failure C1. Worn stem seals. Replace seals and gasket.
C2. Pitted stem, worn stem. Replace plug/stem, seals and gasket.
VII. TROUBLE SHOOTING GUIDE
SEC TION VII