Designs D & DA
6
8. Install a new bonnet gasket (key 7), making sure
the gasket seating surfaces are clean and smooth.
Carefully install the valve plug/stem assembly into the
valve body. Then slide the bonnet over the stem and
thread it tightly into the valve body, per the torque val-
ues in table 4.
9. Install new packing and the metal packing box
parts according to the correct arrangement in figure 3.
Place a smooth-edged pipe over the valve stem, and
gently tap each soft packing part into the packing box.
10. Slide the packing follower, upper wiper, and pack-
ing flange (keys 10, 21, and 12) into position. Lubri-
cate the packing flange studs (key 13) and the faces
of the packing flange nuts (key 15). Install the packing
flange nuts.
11. For spring-loaded PTFE V-ring packing, tighten
the packing flange nuts (key 15) until the packing fol-
lower (key 10) contacts the bonnet. For other packing
arrangements, tighten the packing flange nuts (key 15)
alternately in small equal increments. Continue until
one of the nuts reaches the minimum recommended
torque shown in table 3. Then tighten the remaining
packing flange nut until the packing flange is level and
at a 90-degree angle to the valve stem.
12. Mount the actuator on the bonnet (key 5) and con-
nect the actuator and valve plug stem according to the
procedure in the appropriate actuator instruction
manual. Check for leakage around the packing follow-
er when you put the control valve assembly into ser-
vice. Retighten the packing flange nuts as required.
Trim Maintenance
Refer to figure 4 and 5 for key number locations.
Disassembly
1. Remove the actuator and the bonnet as described
in steps 1 through 3 of the
Replacing Packing proce-
dure.
CAUTION
Use care to avoid damaging the gasket
sealing surfaces.
The stem surface finish of the valve
plug/stem assembly (key 4) is critical for
making a good packing seal. The seat-
ing surfaces of the seat ring (key 2) and
the plug of the valve plug/stem assem-
bly (key 4) are critical for tight shutoff.
Protect these parts from damage if you
plan to re-use them in the valve.
Table 4. Torque for
Body-to-Bonnet Joint
VALVE SIZE,
RECOMMENDED TORQUE
VALVE SIZE,
INCHES
Lbf
S
ft
N
S
m
1
780
1060
2 - 6000
(1)
2 - 10,000
(1)
1500
6700
2030
9080
1. Valve rating.
Table 5. Torque for
Seat Ring (Key 2)
BODY SIZE
RECOMMENDED TORQUE
Inches
mm
Lbf
S
ft
N
S
m
1
25.4
300
407
2
50.8
515
698
2. If you wish, remove the valve plug/stem assembly
(key 4) and the packing parts from the bonnet. If you
plan to re-use the valve plug, tape or otherwise protect
the valve plug seating surface and the stem threads to
prevent damage. Remove the packing parts as de-
scribed in the
Packing Maintenance procedure.
3. Use a socket wrench to remove the seat ring (key
2).
4. Remove the seat ring (key 2) and seat ring gasket
(key 3) from the valve body.
5. Inspect parts for wear or damage that would pre-
vent proper operation of the valve body. Clean the
gasket surfaces.
6. Replace trim parts as necessary or use the
Lapping Metal Seats procedure.
Lapping Metal Seats
A certain amount of leakage should be expected with
metal-to-metal seating in any valve body. If the leak-
age becomes excessive, however, the condition of the
seating surfaces of the valve plug and seat ring (keys
4 and 2, figures 4 and 5) can be improved by lapping.
(Deep nicks should be machined out rather than
ground out.) Use a good quality lapping compound of
a mixture of 280 to 600-grit. Apply the compound to
the bottom of the valve plug.
Partially assemble the valve so the seat ring and valve
plug are in place and the bonnet (with bushing
installed) is screwed hand-tight into the body. Make a
simple handle from a piece of strap iron locked to the
valve plug stem with nuts. Rotate the handle alternate-
ly in each direction with light downward pressure to lap
the seats. If you think there is not enough lubrication
(for example, if you hear a squeaking noise or feel
vibration), stop the procedure, and apply more lapping
compound before continuing. After lapping, remove
the bonnet and valve plug/stem assembly as a unit,
and clean the seating surfaces. Completely assemble
as described in the
Assembly portion of the Trim Main-
tenance procedure.
Test the valve for shutoff. Repeat the lapping proce-
dure if leakage is still excessive.
Содержание D Series
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