The good effect of the latter is
likely to be destroyed by a rapid emptying of the pipe. If the water is
drawn out faster than the air can enter through the air-valves, heavy
vacuums are formed down long slopes, and the air forces its way in
through the joints and between the staves. The result is that the pipe
will frequently leak badly for some time after it is refilled, although
it may have been tight previously.
A full pipe and a steady pressure are highly desirable. This doubtless
accounts to some extent for the extreme tightness of the wood pipe in
the pumping main.
_Grade Lines_.--The hydraulic grade lines, shown on Plate V, were laid
as best fitting the controlling elevations. The various diameters of
pipe were determined by Darcy's general formula, with _C_ = 0.00033 for
wood and = 0.00066 for iron pipe, checking by Kutter's formula, with _n_
= 0.01 for wood and = 0.012 for iron. These coefficients were taken as
conservative and on the safe side, and such they proved to be. It was
desired that the line should carry not less than 5 sec-ft. to Nogal and
half as much beyond.
_Velocities_.--The pipe line from Bonito Creek to the Nogal Reservoir
affords excellent conditions for velocity and capacity measurements,
there being no distribution service from it.
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