Cashco 521 User Manual
Page 15
IOM-521
15
7. Bellows failure.
Possible Causes
Remedies
A. Overstroke of actuator.
A. Recalibrate valve/actuator unit.
B. Abrasive particulate in fl uid.
B. Remove all fl uid particulate.
C. Pressure, temperature, or pressure drop
outside
limits.
C. Bring process variables within range of application; see Graph 1 in 521-TB..
D. Fluid absorption.
D1. Reduce pressure/temperature if possible.
D2. Reduce number of startups/shutdowns, or rapid depressurizations.
E. Frequent stroking causing fatigue failure of
TFE
material.
E1. Stabilize input SIG.
E2. Stabilize positioner output LOAD.
E3. Stabilize process variations to steady state, steady fl ow.
E4. Excess "play" in actuator swivel adapter; replace adapter.
E5. Cycle life reached; replace bellows.
F. Corrosion of embedded nut.
F1. Consult factory.
F2. Use alternate stem material.
8. Corrosion of stem sub-assembly at packing area.
Possible Causes
Remedies
A. Loose packing.
A. Disassemble valve and replace stem. Reassemble and tighten packing.
B. Fluid permeation of bellows.
B1. Bring process variables within range of application; see Graph 1 in 521-TB.
B2. Use alternate stem materials construction.
B3. Locate, or position valve to be out of ambient moisture.
B4. Modify insulation if "trapping" moisture around packing gland nut.
B5. Purge "void zone".
C. Bellows failure.
C. See No. 7 of this section.
9. Corrosion of silver soldered joint in sub-assembly (1-1/2" or 2" sizes only).
Possible Causes
Remedies
A. Fluid permeation with chemical attack of
silver solder.
A1. Use alternate stem materials construction.
A2. Purge "void zone".
10. Corrosion surrounding vented pipe plug on bonnet.
Possible Causes
Remedies
A. Fluid permeation and loose vented pipe plug.
A1. Tighten plug.
A2. Replace corroded plug.
A3. Purge "void zone".
B. Bellows
Failure.
B. Replace
bellows.
11. External corrosion of jacket halves, bonnet, and body and bonnet bolting.
Possible Causes
Remedies
A. Corrosive ambient environment.
A1. Determine location of corrosive fl uid and maintain cause of leakage.
A2. Coat exposed portions with suitable corrosive resistant epoxy to degree able,
12. Blisters on TFE internals.
Possible Causes
Remedies
A. Effects of absorption.
A1. Reduce pressure/temperature levels.
A2. Reduce startups/shutdowns and rapid depressurizations.
A3. Replace body assembly.
13. General corrosion of internals in "void zone", including Belleville washers ,embedded nut, bonnet, anti-rotation stop, and stem.
Possible Causes
Remedies
A. Permeation together with ingress of
moisture in "void zone".
A1. Remove moisture source to greatest degree possible.
A2. Purge "void zone".