CHAPTER7
Il'iSPECfiON
AND
M.AINTEJ.'JANCE
------HANDLES
0
SIGHT
PORT
[FIGURE 7-10 I REAR ACCESS PLUG]
Rear
Access Plug
This plug seals the access crawlway to the com-
bustion chamber into which combustion gases
exit from the furnace tube before entering the
second
pass
tubes.
The refractory face
of
the plug should be in-
spected for deterioration when the boiler
is
opened for inspection.
After removing the rear access plug, clean the
crawlway flange with a scraper
or
wire brush.
Inspect the plug sealing gasket. and replace it if
damaged.
Front Inner Door
The front inner door
is
lined with a lightweight
castable insulation material. Thin "hairline"
cracks may develop after a period
of
time. How-
ever, these will generally tend
to
close due
to
expansion when the boiler
is
fired.
A thin wash-coat mixture applied gently with a
brush
is helpful in maintaining a hard surface.
750-150
Minor repairs can
~
accomplished
by
enlarging
or cutting out affected areas, making certain that
they are clean and then patching
as
required.
Should the entire installation require replace-
ment, remove existing material and clean
to
bare
metal. Inspect
th~
retaining pins and replace if
necessary. Reinforcing wire suitably attached
may also be
used. The recommended insulation
is
known as Vee Block Mix and
is
available
in
SO
lb. bags (CB PIN 872-162).
Mix the material with water to a troweling con-
sistency. Mixing should be completely uniform
with no portion
either
wetter
or
drier than
another. Trowel this mixture into any areas that
are being patched.
If
replacing complete insula-
tion, begin at the bottom
of
thcr
door and apply
the mixture
to a thickness equal to the protecting
shroud. With a trowel, apply horizontally back
and forth across the door
in
layers until the re·
quired thickness
is
reached.
Allow
to
air-dry
as
long
as
possible. If immediate
use
of
boiler
is
required, fire intennittently at low
fire to avoid rapid drying
of
the material.
CHAPTER 7
·19
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