In America many towers
are as much as 100 ft high, but ordinary workmen do not
voluntarily climb to such a height, with the result that the
mill is not properly oiled. About 40 ft is the usual height in
this country, and 60 ft should be used as a maximum.
Mr. George Phelps, in a paper read by him in 1906 before the
Association of Water Engineers, stated that it was safe to
assume that on an average a fifteen miles per hour wind was
available for eight hours per day, and from this he gave the
following figures as representing the approximate average duty
with, a lift of l00 ft, including friction:--
TABLE NO. 14
DUTY OF WINTDMILU
Diameter of Wheel.
10
12
14
16
18
20
25
30
35
40
The following table gives the result of tests carried out by
the United States Department of Agriculture at Cheyenne, Wyo.,
with a l4 ft diameter windmill under differing wind
velocities:--
TABLE No. 15.
POWER or l4-rx WINDMILL IN VARYING WINDS.
Velocity of Wind (miles per hour).
0--5 6-10 11-15 16-20 21-25 26-30 31-35
It will be apparent from the foregoing figures that practically
the whole of the pumping for a small sewerage works may be done
by means of a windmill, but it is undesirable to rely entirely
upon such a system, even if two mills are erected so that the
plant will be in duplicate, because there is always the
possibility, although it may be remote, of a lengthened period
of calm, when the sewage would accumulate; and, further, the
Local Government Board would not approve the scheme unless it
included an engine, driven by gas, oil, or other mechanical
power, for emergencies.
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