how to overhaul control valves.what are the proper procedures.

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how to overhaul control valves.what are the proper procedures...

It is a very lengthy topic. I will try to explain some major point.
1. Mark the parts orientation before dismantling, such as mark at body, bonnet, yoke, pressure chambers casing.
2. Note down the threads upper side and lower side of coupling.
3. Suppose, valve is air to open, open it with direct feeding signal to diaphragm upto 5%.
4. remove the coupling.
5. release load pressure
6. Loose yoke nut and remove yoke from bonnet
7. Remove gland packing nuts,remove gland pusher
8. Dismantle bonnet nuts
9. Remove bonnet from body
10. Remove trim material

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