15.52|19.83|
| 75 | 3.90| 5.64| 7.36| 9.09|10.82|15.16|19.48|
| 80 | 3.48| 5.22| 6.96| 8.70|10.44|14.79|19.13|
| 85 | 3.06| 4.80| 6.55| 8.30|10.05|14.41|18.78|
| 90 | 2.63| 4.39| 6.14| 7.89| 9.65|14.04|18.43|
| 95 | 2.20| 3.97| 5.73| 7.49| 9.25|13.66|18.07|
| 100 | 1.77| 3.54| 5.31| 7.08| 8.85|13.28|17.70|
| 110 | .89| 2.68| 4.47| 6.25| 8.04|12.50|16.97|
| 120 | .00| 1.80| 3.61| 5.41| 7.21|11.71|16.22|
| 130 | | .91| 2.73| 4.55| 6.37|10.91|15.46|
| 140 | | .00| 1.84| 3.67| 5.51|10.09|14.68|
| 150 | | | .93| 2.78| 4.63| 9.26|13.89|
| 160 | | | .00| 1.87| 3.74| 8.41|13.09|
| 170 | | | | .94| 2.83| 7.55|12.27|
| 180 | | | | .00| 1.91| 6.67|11.43|
| 190 | | | | | .96| 5.77|10.58|
| 200 | | | | | .00| 4.86| 9.71|
| 210 | | | | | | 3.92| 8.82|
+-----------+-----+-----+-----+-----+-----+-----+-----+

Besides the saving in fuel effected by the use of feed water heaters,
other advantages are secured. The time required for the conversion of
water into steam is diminished and the steam capacity of the boiler
thereby increased. Further, the feeding of cold water into a boiler has
a tendency toward the setting up of temperature strains, which are
diminished in proportion as the temperature of the feed approaches that
of the steam. An important additional advantage of heating feed water is
that in certain types of heaters a large portion of the scale forming
ingredients are precipitated before entering the boiler, with a
consequent saving in cleaning and losses through decreased efficiency
and capacity.

In general, feed water heaters may be divided into closed heaters, open
heaters and economizers; the first two depend for their heat upon
exhaust, or in some cases live steam, while the last class utilizes the
heat of the waste flue gases to secure the same result. The question of
the type of apparatus to be installed is dependent upon the conditions
attached to each individual case.

In closed heaters the feed water and the exhaust steam do not come into
actual contact with each other. Either the steam or the water passes
through tubes surrounded by the other medium, as the heater is of the
steam-tube or water-tube type. A closed heater is best suited for water
free from scale-forming matter, as such matter soon c