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Baker Hughes
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XII. Inspection and Part Replacement (Cont.)
Figure 10: HP Thermodisc
1. Once a minimum dimension is met, disc is to be discarded.
1811-HP Thermodisc Machining Dimensions
Table 4: Thermodisc Replacement Criteria
1
Orifice
F min
in.
mm
F
.020
0.51
G
.020
0.51
H
.020
0.51
J
.020
0.51
K
.020
0.51
L
.020
0.51
M
.020
0.51
N
.020
0.51
P
.030
0.76
Q
.030
0.76
Note:
Due to the thin seat lip, Thermodisc can not be machined. Damage, if present, may be removed
by lapping unit “F” (min.) is exceeded. The Thermodisc requires replacement when the “F” (min.)
dimension is exceeded
If you find flexible seating configurations different from those shown in Figures 9 & 11,
replacement with the current, improved design Thermodisc is recommended.
The 1811-HP & LP Thermodisc is designed for
steam service, and are standard on all new 1811
Safety Valves. The Thermodisc prevents most seat
damage by maintaining a tight seal at higher operating
pressures than the Flat Solid Disc. Inspect the disc
seat for steam cuts, nicks, or other damage. If minor
damage has occurred, the seat may be restored by
lightly lapping seat area G, as indicated in Figures 9 &
10. Do not machine Thermodisc.
If dimension F is reduced to the minimum indicated
in Table 4, the disc should be replaced. Other
replacement criteria include thread damage, spindle
bearing surface damage and severe galling. Egging
caused by vibration and wear also require replacement
to maintain “like new” valve performance.
D
C
N
15
0
45
0
Figure 11: LP Flat Solid Disc & Thermodisc
