416 feet. The entrance into the pen-stock was tapered, so that the
coefficient of contraction was about 0.92. For pressures not exceeding say
380 feet, the joints were put together stove-pipe fashion. For greater
pressures, the joints were made by an inner sleeve riveted on one end of
the joint, with an outer lap-welded band, as shown by Fig. 15; lead was
run into the space between the outer band and the pipe, and then tightly
driven up by calking-irons. The pipe was laid under the bed of the Big
Canon Creek, a large stream when in freshet, where the head below the
hydraulic grade line was 760 feet. Some of the lead joints leaked slightly
at first, but this was soon remedied by more careful calking. No man-holes
or escape-gates were used. The pipe for the larger part of the year is not
filled at its upper end; when such is the case, the water at the inlet
carries down the pipe a great quantity of air, for which escapes must be
provided to prevent a jarring or throbbing, which would soon destroy the
pipe. The escape air-valves used are shown by Fig. 16. They consist simply
of a heavy flap valve of cast-iron, with recess for lead filling to give
greater weight set on top the pipe, seating on a vulcanized rubber
cushion, and swinging on a loose hinge.
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