MAIN VALVE TESTING
All tests can be performed on main valve while it remains
installed in the steam system, if there are gate valves
located upstream and downstream of the main valve.
1. Isolate the main valve from steam pressure by closing
the gate valves that are located upstream and down-
stream of the main valve.
2. If the main valve has a spring pilot or air pilot installed
on it, close the shut off valve in the feedback line to
the spring or air pilot.
3. Disconnect the pilot valves from the main valve.
4. Remove the orifice fitting from the 1/8" NPT port
located on the side of the main valve.
Test for Leakage between Plug and Seat:
1. Attach an air line to the 1/4" NPT port located on the
side of the main valve inlet.
2. Apply air to the main valve inlet.
3. Check for air leakage from the 1/8" NPT port on the
side of the main valve outlet.
• Only a small amount of leakage is allowable.
• Excessive leakage indicates either worn seat or
plug, or the seat is held open by dirt.
• Clean seat and plug and retest.
• Replace parts if necessary.
Test for Damaged Diaphragm:
1. Plug the 1/4 NPT port on the side of the main valve
inlet.
2. Attach an air line containing a pressure regulating
valve (PRV) and pressure gauge to the 1/8 NPT port
located in the center of the lower diaphragm case of
the main valve.
3. While adjusting the PRV in the air line, slowly
increase the air pressure on the main valve
diaphragms from 0 psig to 30 psig (0 to 2.1 bar).
Slowly decrease the pressure back to 0 psig (0 bar).
Repeat this step several times.
4. Check for air leakage from the open 1/8" NPT port on
the side on the main valve outlet while the air pres-
sure is being cycled.
• No air leakage is permitted.
• Large air leakage indicates the diaphragms are
cracked or broken.
• Replace new diaphragms as needed.
Test for Restricted Movement:
1. Attach an air line containing a pressure regulating
valve (PRV) and pressure gauge to the 1/8 NPT port
located in the center of the lower diaphragm case of
the main valve.
2. Disassemble the top cover from the main valve.
3. While adjusting the PRV in the air line:
• Look in the top of the main valve
• Slowly increase and decrease the air pressure to
the lower diaphragm case.
4. Increase and decrease the air pressure several times.
5. Watch the movement of the main valve stem and plug.
6. Check for jerky movement or no movement.
• The valve should stroke smoothly between the fully
closed and fully open positions within the following
pressure limits:
• Jerky movement indicates the valve stem and
bushing are worn or diaphragms are damaged.
• Test for damaged diaphragms as described above.
• If diaphragms are not damaged, install a new stem
and bushing.
Pressure at
Pressure at Full
Main Valve
Start of Stroke
Stroke
Model
psig (bar)
psig (bar)
2100
2.0 to 6.5
18.0 to 29.0
2200
(0.14 to 4.5)
(1.2 to 2.0)
2300
2150
0.5 to 2.0
3.5 to 7.0
2250
(0.03 to 0.14)
(0.24 to 5)
13
