sing pressure tanks is more complete than either
of the others, comprising engine, pump, air compressor, a water tank,
and also an air tank. It is best described by a recent example
constructed from plans and under the direction of the writer. The
buildings supplied with water comprise the mansion, the stable, the
cottage, and a dairy, and the pumping station is placed near the
shore of the lake from which the supply is taken. See Figs. 1 and 2.

[Illustration: FIG. 1.

DIAGRAM OF COMPRESSED AIR TANK SYSTEM.]

[Illustration: FIG. 2.

PRESSURE-TANK PUMPING STATION.

Interior view of pumping station of compressed air-tank system (see
plan on opposite page) showing 3,000 gallon water tank, air tank of
150 pounds pressure and 10 horse-power gasoline engine.]

The pump house is about 20 feet by 27 feet, and contains a
water-storage tank 6 feet in diameter and 13-1/2 feet long, of a
capacity of 3,000 gallons; an air tank of same dimensions as the water
tank, holding air under 150 pounds pressure; a 10 horse-power gasoline
engine, direct-connected, by means of friction clutch, with an air
compressor and also with a triplex pump of 75 gallons capacity per
minute.

The water in the tank is kept under 75 pounds pressure, and at the
hydrant near the house, located about 100 feet above the pumping
station, there is an available pressure of 33 pounds. The last drop of
water flows from the water tank under the full pressure of 75 pounds
at the pumping station. The suction pipe into the lake is 4 inches and
is provided with well strainers to prevent clogging.

The cost of pumping water by this system is quite reasonable. The
gasoline engine requires per horse-power per hour about 1-1/4 gallons
of gasoline, and at sixteen cents per gallon this makes the cost for
1,000 gallons pumped about five cents. To this expense should,
however, be added the cost of lubricating oil, repairs, amount for
depreciation, and the small cost for labor in running the engine.

Water pipes forming a distribution system should always be chosen
generous in diameter, in order to avoid undue loss of pressure by
friction. Where fire hydrants are provided, the size of the water main
should not be below four inches. All branches should be controlled by
shut-offs, for which the full-way gate valves are used in preference
to globe valves. Pipe-line material is usually galvanized,
screw-jointed wrought iron for sizes up to four inches.

In conclusion, a w