Water Level Alarms.
Where it is desired to signal the rising or falling of water in a tank above or below a given point, a water level indicator as in [Fig. 41] may be used.
A hollow ball H is mounted on the end of a rod which slides vertically in guides, not shown. Adjustable stops S S press against a spring arm R, pressing it up or down, according as the water level is rising or falling. If rising, R makes contact with the adjustable screw A, if falling, with D, in both cases completing the electrical circuit of the battery C and bell B.
Fig. 41
Another and simpler form is shown in [Fig. 42], where the ball H is mounted on the end of a lever L pivoted at P, its rise or fall completing the circuit of B and C as before.
Where it is desired to give a different signal for the rise and the fall of level, two bells B and E ([Fig. 43]) may be used connected as shown. The rising of the ball will ring bell B, and its fall, bell E.
Fig. 42
Fig. 43
In both forms of indicator, a means must be provided that an undue rise may not bend the lever. This may be accomplished by using contact springs instead of contact screws; it is, however, then harder to adjust the indicator to fine differences of level.
In all cases the contacts must be faced with platinum to prevent corrosion.