MAIN VALVE REPAIR
Main Valve Repair
Main valves can be repaired without removing them from
the piping.
Note: If a specific problem has been located during testing,
only complete the steps required to complete repair of the
damaged parts.
1. Isolate the main valve from the steam line. Make sure
the internal pressure is 0 psig and allow the valve to
cool to prevent injury.
2. Remove the main valve top cover plate (and stem top
guide bushing on larger units).
3. Connect a source of regulated air pressure to the 1/8"
NPT port located in the center of the lower diaphragm
case of the main valve.
4. Load the main valve diaphragm chamber with 60-80
psig (4.2 to 5.6 bar) air to fully open the main valve
seat.
5. Remove the stem nut, lock washer and plug from the
stem by using an open end wrench on the stem nut
and a hex Allen key in the end of the stem to keep the
stem from rotating.
Important: do not release the air
pressure from the main valve diaphragm with these
parts off because the spring tension will damage the
diaphragms.
Note: If the stem unscrews from the diaphragm button,
remove the entire stem assembly from the main valve.
• Carefully clamp on the stem with a pair of channel
locks well above the guide bushing area and remove
the nut, washer and plug.
• Reinstall the valve stem using a hex wrench in the
end of the stem to tighten the stem into the diaphragm
button. See "Tightening Torque for Series 2000 Main
Valve" chart, page 15.
6. Inspect the valve seat and plug for deep scratches or
deposits.
• Replace if necessary.
A special seat tool is available
to remove the seat from the body.
• Heating the seat with a torch may be required for
seat removal.
7. Coat the threads and lower edge of seat flange with a
high temperature non-hardening sealant before
installing a new seat.
8. Install a new seat. A new plug and seat will require
lapping. See "Main Valve Seat Lapping Procedures,"
below.
9. To continue disassembly:
• Replace plug and stem nut onto stem to prevent
damage to diaphragm when air pressure is released.
Do not fully tighten nut.
• Relieve air pressure from the diaphragm cover.
• Unbolt the diaphragm cover and remove the
diaphragms.
• Compress the spring to lift the plug off the seat.
• Remove the plug and allow the spring to relax.
• Remove the button, stem and spring.
10. Clean the stem and guide bushing. Replace if worn.
11. Reassemble the valve in the reverse order of the
disassembly procedure described above. See
"Tightening Torque for Series 2000 Main Valve" chart,
page 15.
12. Return valve to service.
13. Check for proper operation.
Main Valve Seat Lapping Procedures
Main valve seat lapping may be required on new
installations where dead end service is required.
Lapping is also required when a new plug and seat
are installed in a main valve.
1. Isolate the main valve from the steam line. Make sure
the internal pressure is 0 psig and allow the valve to
cool to prevent injury.
2. Remove the main valve top cover plate. On larger
units, remove the stem top guide bushing.
3. Connect a source of regulated air pressure to the 1/8"
NPT port located in the center of the lower diaphragm
case of the main valve.
4. Load the main valve diaphragm chamber with 60-80
psig air to fully open the main valve seat.
5. Remove the stem nut, lock washer and plug from the
stem by using an open end wrench on the stem nut
and a hex Allen key in the end of the stem to keep the
stem from rotating.
Important: do not release the air
pressure from the main valve diaphragm with these
parts off because the spring tension will damage the
diaphragms.
Note: If the stem unscrews from the diaphragm button,
remove the entire stem assembly from the main
valve.
• Carefully clamp on the stem with a pair of channel
locks well above the guide bushing area and
remove
the nut, washer and plug.
• Reinstall the valve stem using a hex wrench in the
end of the stem to tighten the stem into the
diaphragm button. See "Tightening Torque for
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