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COMBUSTION AND BOILKH SIOTTIN'CJS .'&/
a pressure against the top of the setting proportional to their
vertical height and their average temperatures in Ilio same manner
asa chimney. The gases in the first pass, being lighter Ifinn those
in the second pass, exert more pressure and therefore tend (o foree
the gases in the second pass down and under the second Imflle.
In the third pass this uplift tends to accelerate the movement of
the gases to the smoke flue. The greater the height of I IK* set! in«
the greater the upward pressure. These pressures will nntumlly
affect the reading of any draft gage attaehod to the boiler. The
dynamic pressure due to velocity of flow nuiy have nn additive
or subtractive effect on the reading of the dniff. pi^e^depeiidinK
upon its location or, more correctly, upon the. lonilion of the*
connections to the setting.
In connection with baffles designed ostensibly to inerea.sc Hie
velocity of flow of the off gases of combustion Ihe following fable
gives the volumetric air supply and the resulting off #iseH from
an exceptionally good grade of coal having a very low nsh content.
Volume at 0° C. und
gram Con I
Air supply 100 per cent .
9 . 04
" 110 per cent.
' ' 120 per cent .
' ' 140 per cent .
' l 150 per cent .
' ' 175 per cent .
15 . 57
" 200 per cent.
WnHf.<* C JIIM
C "i ml
.................... 1:w ......... '"
27H ! 2HI
As the composition of the coal varie.s, those* volumes will vary.
The coal consumption per boiler horsepower will vnry from two
pounds per hour upward and the total amount of roal hnnml cm it
grate will depend upon the size of the boiler ami (he amount if in
forced above its nominal rating. As largo HIWH nn* the incwt
interesting an 875 horsepower Sterling type* boiler ojrntfed ni
several loads will be considered. The volume* inside the net ting J«