ean
condition cannot be emphasized too strongly.

The internal cleaning can best be accomplished by means of an air or
water-driven turbine, the cutter heads of which may be changed to handle
various thicknesses of scale. Fig. 41 shows a turbine cleaner with
various cutting heads, which has been found to give satisfactory
service.

Where a water-driven turbine is used, it should be connected to a pump
which will deliver at least 120 gallons per minute per cleaner at 150
pounds pressure. This pressure should never be less than 90 pounds if
satisfactory results are desired. Where an air-driven turbine is used,
the pressure should be at least 100 pounds, though 150 pounds is
preferable, and sufficient water should be introduced into the tube to
keep the cutting head cool and assist in washing down the scale as it is
chipped off.

Where scale has been allowed to accumulate to an excessive thickness,
the work of removal is difficult and tedious. Where such a heavy scale
is of sulphate formation, its removal may be assisted by filling the
boiler with water to which there has been added a quantity of soda ash,
a bucketful to each drum, starting a low fire and allowing the water to
boil for twenty-four hours with no pressure on the boiler. It should be
cooled slowly, drained, and the turbine cleaner used immediately, as the
scale will tend to harden rapidly under the action of the air.

Where oil has been allowed to get into a boiler, it should be removed
before placing the boiler in service, as described previously where
reference is made to its removal by boiling out with soda ash.

Where pitting or corrosion is noted, the parts affected should be
carefully cleaned and the interior of the drums should be painted with
white zinc if the boiler is to remain idle. The cause of such action
should be immediately ascertained and steps taken to apply the proper
remedy.

When making an internal inspection of a boiler or when cleaning the
interior heating surfaces, great care must be taken to guard against the
possibility of steam entering the boiler in question from other boilers
on the same line either through the careless opening of the boiler stop
valve or some auxiliary valve or from an open blow-off. Bad accidents
through scalding have resulted from the neglect of this precaution.

Boiler brickwork should be kept pointed up and all cracks filled. The
boiler baffles should be kept tight to prevent by-passing of any gases