Cashco DA2 - Positive Differential - Manual (Page 14)

IOM-DA2 14
4. Diaphragm continually breaks (steam service regulators).
Possible Causes Remedies
A. Stem seals (14) which protect fl uorocarbon elastomer in
diaphragm assembly may have deteriorated.
A. Replace with new stem seals (14).
B. Diaphragm nut (7) may not be torqued to proper value. B. Confi rm torque value in accordance with Section VII, para-
graph F-7.
C. Diaphragm too stiff causing it to crack in service. C. Follow proper preforming and air evacuation techniques
during diaphragm installation in accordance with Section
VII, paragraph F-12.
5. Diaphragm continually breaks (all regulators).
Possible Causes Remedies
A. Differential pressure across diaphragm may have
exceeded limits. (See Table 1) A. Be aware of limits as well as where the various pressures are
acting. Install pressure safety equipment as necessary.
6. Leakage at diaphragm fl ange.
Possible Causes Remedies
A. Body bolts not torqued properly. A. Torque to proper value (see Section VII, paragraph F-13).
B. Pressures at diaphragm may be too high for regulator
design.
B. Consult factory.
7. Leakage across seat.
Possible Causes Remedies
A. Contamination (debris) in regulator. A1. Remove internals, clean and if necessary, replace sealing
and seating elements.*
A2. "Coin" seat if V-TFE or CTFE seat material.
B. Oversized regulator; valve plug operates directly next to
seat. B. Check actual fl ow conditions; resize regulator for minimum
and maximum fl ow; if necessary, replace with smaller
regulator.
* Excess seat leakage may be diagnosed when a failure of the dynamic side seal has occurred. Inspect both potential
internal leak paths.