The conditions regarding the temperature of the furnace and boiler, the
quantity and quality of the live coal and ash on the grates, the water
level, and the steam pressure, should be as nearly as possible the same
at the end as at the beginning of the test.
To secure the desired equality of conditions with hand-fired boilers,
the following method should be employed:
The furnace being well heated by a preliminary run, burn the
fire low, and thoroughly clean it, leaving enough live coal
spread evenly over the grate (say 2 to 4 inches),[64] to serve
as a foundation for the new fire. Note quickly the thickness of
the coal bed as nearly as it can be estimated or measured; also
the water level,[65] the steam pressure, and the time, and
record the latter as the starting time. Fresh coal should then
be fired from that weighed for the test, the ashpit throughly
cleaned, and the regular work of the test proceeded with. Before
the end of the test the fire should again be burned low and
cleaned in such a manner as to leave the same amount of live
coal on the grate as at the start. When this condition is
reached, observe quickly the water level,[65] the steam
pressure, and the time, and record the latter as the stopping
time. If the water level is not the same as at the beginning a
correction should be made by computation, rather than by feeding
additional water after the final readings are taken. Finally
remove the ashes and refuse from the ashpit. In a plant
containing several boilers where it is not practicable to clean
them simultaneously, the fires should be cleaned one after the
other as rapidly as may be, and each one after cleaning charged
with enough coal to maintain a thin fire in good working
condition. After the last fire is cleaned and in working
condition, burn all the fires low (say 4 to 6 inches), note
quickly the thickness of each, also the water levels, steam
pressure, and time, which last is taken as the starting time.
Likewise when the time arrives for closing the test, the fires
should be quickly cleaned one by one, and when this work is
completed they should all be burned low the same as the start,
and the various observations made as noted. In the case of a
large boiler having several furnace doors requiring the fire to
be cleaned in sections one after the other, the above directions
pertaining to starting and stopping in a plant of several
boilers may be followed.
To obtain the desired equality of conditions of the fire when a
mechanical stoker other than a chain grate is used, the procedure should
be modified where practicable as follows:
Regulate the coal feed so as to burn the fire to the low
condition required for cleaning. Shut off the coal-feeding
mechanism and fill the hoppers level full. Clean the ash or dump
plate, note quickly the depth and condition of the coal on the
grate, the water level,[66] the steam pressure, and the time,
and record the latter as the starting time. Then start the
coal-feeding mechanism, clean the ashpit, and proceed with the
regular work of the test.
When the time arrives for the close of the test, shut off the
coal-feeding mechanism, fill the hoppers and burn the fire to
the same low point as at the beginning. When this condition is
reached, note the water level, the steam pressure, and the time,
and record the latter as the stopping time. Finally clean the
ashplate and haul the ashes.
In the case of chain grate stokers, the desired operating
conditions should be maintained for half an hour before starting
a test and for a like period before its close, the height of the
throat plate and the speed of the grate being the same during
both of these periods.