Table 5-1. Seat ring tightening torque
Unit: N·m
Connection diameter (inches) Seat ring tightening torque
1/2, 3/4, 1 140 to 150
1-1/2, 2 210 to 230
2-1/2, 3 340 to 380
4 590 to 650
Table 5-2. Bonnet hex nut tightening torque
Unit: N·m
Connection diameter (inches) Bonnet hex nut Tightening torque
1/2, 3/4, 1 M10 39 to 43
1-1/2, 2 M16 88 to 97
2-1/2, 3 M16 88 to 97
4 M16 88 to 97
Table 5-3. Packing flange hex nut tightening torque
Unit: N·m
Valve stem size PTFE* yarn packing V-shaped PTFE packing
φ 13 mm
6 0.8
φ 16 mm
16 0.8
φ 30 mm
34 0.8
* Polytetrafluoroethylene
Note: The torque may vary depending on the type of packing. Use the indicated torque as a rough
guideline.
(2) Lap the contacting surfaces
Lap the mating valve plug and the seat ring surfaces.
Step Procedure
1 Put an old gasket in place on the valve.
2 Apply a small amount of compound to the surface of the seat ring where the valve plug
makes contact.
3 Insert the valve plug into the bonnet, and mount the bonnet on the valve loosely with
stud bolts and nuts.
4 To keep the stem at the center during lapping, insert old packing into the gland.
5 Press the valve plug gently onto the seat ring and turn the plug to lap it (if you attach
the stem connector to the top of the valve plug, you can use it as a knob). Remove the
bonnet and valve plug from the valve, and check that there are no fine scratches, etc., on
the surface.
6 When lapping is complete, wipe off the compound. Remove the stem connector, old
packing, and old gasket.
5-9
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