What does a valve overhaul involve?

In short: a valve overhaul returns a valve to serviceable condition. The valve is dismantled, cleaned and inspected; worn or damaged parts are repaired or replaced; and the valve is reassembled and pressure tested before it is returned to service.

When is an overhaul needed?

Common reasons include seat leakage, a gland that keeps leaking after adjustment, stiff or incomplete operation, visible corrosion or erosion, a failed test, or a planned shutdown where valves are removed for inspection anyway.

The usual stages

1. Identification. The valve is tagged and its type, size, rating and condition are recorded on arrival.
2. Dismantling and cleaning. The valve is taken apart and cleaned so the internal surfaces can be inspected properly.
3. Inspection. Seats, closure member, stem, body and bonnet are examined for wear, damage and corrosion, and the repair scope is agreed.
4. Repair. Sealing surfaces are restored, worn parts are machined or replaced, and soft goods such as gaskets and packing are renewed.
5. Reassembly. The valve is rebuilt with bolting tightened correctly.
6. Testing. Pressure and leak tests confirm that the body holds pressure and the seats seal. Safety valves are also checked for set pressure.
7. Documentation. Test results are recorded so the valve's history is available for the maintenance file.

Repair or replace?

Overhaul is usually the better option when the body is sound and parts are available, or when lead times for a new valve are long. Replacement may make sense when the body is badly eroded or the valve is obsolete.