Lapping Metal Seats - Fisher Design ED series Instruction Manual

VALVE STEM DIAMETER
mm Inches
9.5 9.5 3/8 3/8
12.7 12.7 1/2 1/2
19.1 19.1 3/4 3/4
25.4 25 4 1 1
31.8 31 8 1 1/4 1-1/4
The surface finish of the valve stem
(key 7) is critical for making a good
packing seal. The inside surface of the
cage or cage/baffle assembly (key 3), or
cage retainer (key 31), is critical for
smooth operation of the valve plug and
for making a seal with the piston rings
(key 6). The seating surfaces of the valve
plug (key 2) and seat ring (key 9) are
critical for proper shutoff. Unless
inspection reveals otherwise, assume all
these parts are in good condition and
protect them accordingly.
2. Remove the packing flange nuts, packing flange,
upper wiper, and packing follower (keys 5, 3, 12, and
13, figure 18). Carefully push out all the remaining
packing parts from the valve side of the bonnet using a
rounded rod or other tool that will not scratch the
packing box wall. Clean the packing box and the metal
packing parts.
3. Inspect the valve stem threads and packing box
surfaces for any sharp edges which might cut the
packing. Scratches or burrs could cause packing box
leakage or damage to the new packing. If the surface
condition cannot be improved by light sanding, replace
the damaged parts.
4. Remove the load ring (key 26) from an 8-inch
Design ED valve, or the cage adaptor (key 4) from any
restricted-trim valve through 4 inches, and wrap it for
protection.
5. On a 6-inch Design ED valve with a Whisper Trim
III cage or WhisperFlo trim, remove the bonnet spacer
(key 32) and bonnet gasket (key 10) on top of the
spacer. Then on any construction with a cage retainer
(key 31), remove the cage retainer and its associated
gaskets. A Whisper Trim III and WhisperFlo cage
Design ED & EAD Class 125-600
Table 4. Recommended Torque for Packing Flange Nuts
GRAPHITE TYPE PACKING
Minimum
CLASS
Torque
NSm LbfSin
125, 150 3
250, 300 4
600 6
125, 150 5
250, 300 7
600 9
125, 150 11
250, 300 15
600 21
300 26
600 35
300 36
600 49
Maximum
Torque
NSm LbfSin
27 5 40
36 6 53
49 8 73
44 8 66
59 10 88
81 14 122
99 17 149
133 23 199
182 31 274
226 38 339
310 53 466
318 54 477
437 74 655
retainer has two 3/8-inch-16 NPT tappings in which
screws or bolts can be installed for lifting.
6. Remove the cage or cage/baffle assembly (key 3)
and the associated gaskets (keys 10, 11, and 12), and
shim (key 51 for the Design ED valve, key 27 for the
Design EAD valve). If the cage is stuck in the valve,
use a rubber mallet to strike the exposed portion of the
cage at several points around its circumference.
7. Remove the seat ring or liner (key 9), seat ring
gasket (key 13), and the seat ring adaptor (key 5) and
adaptor gasket (key 14) where used in a restricted-trim
seat ring construction.
8. Inspect parts for wear or damage which would
prevent proper operation of the valve. Replace or
repair trim parts according to the following procedure
for Lapping Metal Seats or other valve plug
maintenance procedures as appropriate.

Lapping Metal Seats

CAUTION
To avoid damaging the ENVIRO-SEAL
bellows seal bonnet assembly, do not
attempt to lap the metal seating
surfaces. The design of the assembly
prevents rotation of the stem and any
forced lapping rotation will damage
internal components of the
ENVIRO-SEAL Bellows Seal bonnet.
With metal-seat constructions, seating surfaces of the
valve plug and seat ring or liner (keys 2 and 9, figure
19, 20, or 21) can be lapped for improved shutoff.
(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 compound to the
bottom of the valve plug.
PTFE TYPE PACKING
Minimum Maximum
Torque Torque
NSm LbfSin NSm
1 13 2
2 17 3
3 23 4
2 21 4
3 28 5
4 39 7
5 47 8
7 64 11
10 87 15
12 108 18
17 149 25
17 152 26
24 209 36
LbfSin
19
26
35
31
42
58
70
95
131
162
223
228
314
9