TRIM MAINTENANCE
Disassembly
1. Remove the actuator from the bonnet. Refer
to steps 1 thru 5 of Replacing Packing
procedure. Observe all warnings and cautions.
NOTE: Avoid damaging gasket sealing surfaces.
The surface finish of the valve stem is critical for
ensuring a tight seal. The seating of the seat ring
and valve plug are critical for tight shutoff.
Replace accordingly should an inspection show
damage.
2. Carefully lift the valve plug and stem
assembly, cage, seat ring and seat ring gasket
out of the valve body. If the valve plug is
being re used, take care to protect the valve
plug stem and valve plug seating surface from
scratches or damage.
3. Inspect all components for wear or damage
that would prevent proper operation of the
valve. Replace or repair trim parts
accordingly. Refer to Lapping Metal Seats or
Trim Replacement as required.
Lapping Metal Seats
With metal to metal seating in any valve, a
small amount of leakage can be expected. If
the leakage becomes excessive, it is possible
to improve shutoff by seat lapping of the
valve plug and seat ring.
Deep nicks may be machined, rather than
ground out.
Apply a good quality lapping compound
mixture of 280 to 600 grit to the bottom of
the valve plug.
Secure the seat ring using a vise, and hold the
cage against the seat ring to properly align the
valve plug and seat ring while grinding.
Once completed, clean the seating surfaces
thoroughly and test for shutoff. Repeat the
lapping process if leakage is still excessive.
Assembly
Upon completion of trim maintenance or
replacement, reassemble the valve body using
the following procedure. Ensure all gasketed
surfaces have been thoroughly cleaned.
1. Install the seat ring gasket (key 6) and the seat
ring (key 11) into the valve body.
2. For standard cage installation, align two of
the holes in the cage with the centerline of
the valve body.
3. Install the valve plug and stem assembly (key
4) into the cage. Ensure the m-flat valve plug
orientation is as shown in Figure 5 when
replacing the bonnet.
4. Install the bonnet gasket (key 5) and bonnet
(key 2) over the valve stem and onto the
body.
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