purpose. They are tack-welded in place and can be removed when you are installing the new liner. If they are not removed, make sure the liner has clearance between this clip and the end of the refractory to allow for expansion in this direction.

Depending upon the design pressure of the boiler, the furnace may be of the corrugated type. Although it is not necessary to fill in the depressions for convenience of installation, some or all of the corrugation valleys may be filled with insulating cement. The liner tile should be fitted tightly against the crown of the corrugations.

The furnace extension of the boiler or a dry oven is shown in figure 2-21. The throat tile should be installed flush with the front of the oven and should fit tightly against its sides. The two rows of furnace tile should be fitted tightly against the furnace wall. It is not necessary to allow for expansion.

It is recommended that the tile be dry fitted, match marked, removed, and then reinstalled with the proper amount of refractory cement. Thin joints are desirable.

Generally, it is necessary to shave a portion from one or more tiles to obtain a fit. If a fill piece is required, cut it to fit and install this piece at the bottom of the furnace. It is important to have a good seal between-the burner housing and the throat tile. Liberally coat-the sealing area with an insulating pulp cement or equivalent mixed with water before swinging the burner housing into place.

The rear door is a steel shell containing horizontal baffle tiles and lined with insulation material and a castable refractory (fig. 2-19).

Burned or discolored paint on the outer surface of the door does not necessarily indicate refractory trouble but may be an indication of other conditions such as the following:

Leaking gaskets.

Improper seal.

Door retaining bolts insufficiently or unevenly tightened.

Air line to the rear sight tube is blocked or loose.

Figure 2-21. - Furnace liner refractory—125-150-200 hp.