370

NICHOLLS'S SEAMANSHIP

NAUTICAL KNOWLEDGE

the length of the column in a water gauge would be 3 feet, but the
column in a mercury gauge would only be about 2*6 inches, namely, 36
inches divided by 13-59=2-6 inches. A control valve, (4) in Figure 8,
connects the air pump with the balance chamber, or the chamber with
the gauge, or disconnects all three components as required.

gLO O 00 00

Fig. 11.—Fuel Oil Tank Gauges.
The illustration shows a typical ship installation, The balance
chambers are seen in the double bottom tank> the copper air pipe is
carried up above the load water'line and down again to gauges in the
engine-room. The filling pipes for running in oil are indicated by
hatched lines.