In the event that a valve is in need of repair, only personnel who have been trained in the appropriate repair techniques should conduct repairs. In addition, a full reference manual of manufacturer's instructions should be accessible.
Usually, the manufacturer's instruction manual will provide limits for inspection and rework of this critical part. The seat step, seat diameters and disc holder bearing surfaces are of particular interest.
Re-machining of control rings is not recommended. If damaged, they should be replaced.
The points listed above are also applicable to pilot operated valves. In addition, all elastomers should be replaced as part of any disassembly.
Records should be kept of the "as found" adjustment of adjusting bolt and adjusting rings. This allows for resetting of adjustable members after overhaul prior to final testing.
Valves should be reassembled in the reverse order of disassembly. After reassembly of restored components, final testing and adjustment must be completed. Depending upon the test apparatus employed, final ring adjustments may not be made until after the set pressure has been determined. lf a low volume test stand is used, a "bench setting" will be employed for pressure adjustment. The rings may then be replaced in the "as found" position. AII final adjustments must be sealed. Seals should be traceable and assigned only to qualified personnel.