Deming graphic. (Deming, N.M.) 1903-1948, 1913-11-21
Power REQUIRED for Irritation

=
taken unless the cost for pumping
will not be ont of proportion to the
increased yield that can be produced.
Since pumping cost is u continuous
expense it should receive first con-
sideration, cost of plant, deprecia-
ton, etc., really being secondary
matters.
Irrigation from wells when reduced
to what might be called the first ele-
ments, becomes a problem of lifting
a given weight Ga certain amount of
water) a specified number of feet IN
given time. Since horsepower Is
defined in just these terms. it would
seem that il should be an easymatter
for the farmer contemplating irrlga-
ton to make close estimate Of the
power required to do his work. Like
many other seemingly simple propo-
sitions, there are so many elements
that enter into and effect results. that
only rough approximation can be
made. Such an approximation. how
ever, should serve very useful pur'
pose in that it will help one TO de-
termine whether or not irrigation by
pumping is Il feasible proposition.
The question of how great dis
lance it will be necessary to lift the
water is. as a rule, readily answered.
One should bear in mind, however.
that the water will be nearer the SUR
face in the district where little or no
pumping has been done than II will
be when large number of wells are
in operation. The point in this case,
as applies all along. is that from
practically every standpoint one
should figure the power considerably
higher than the conditions seemingly
require.
The first factor mentioned. that of
the amount Of water to be lifted, Is
so modified by local conditions, that
no general statement can be even
ventured. To estimate closely, one
must take into consideration not only
the number of acres to be irrigated.
but the crop to be raised. kind and
character of soil. prevailing tempera-
lures, average yearly and monthly
rainfall. etc.
The power required for pumping
depends upon the weight of the liquid
to be lifted and the distance il must
be raised. Distance in this case
means the vertical height from source
of supply to the highest point of de-
livery. In practice. allowance must
be- made for the losses in the pump
ing equipment prop,t, and FRACTIONAL
losses in pipe lines.
One horse power is equivalent to
lifting n weight of $4,000 pounds n
distance of one foot in one minutes
time. To find the power required for
pumping in terms of horsepower
one therefore multiplicS the number
of gallons of water TO he raised by
the weight per gallon IS l-3 pounds
and this product by the height il
feet the water is to be lifted. This
product divided by $4,000 gives the
theoretical horsepower required.
In other words. multiply the num-
Der of gallons to be pumped per min
ute by the number of feet the water
is to be raised. and divide by 1000
The result obtained by the above
makes no allowance for losses, and
therefore, to get the horsepower ac.
tually required, one must know thu
efficiency of the pump he is using
of the engine driving same, to whicl
must be added losses due to friction
in pipe and belt losses if belt drive il
used.
Figuring actual power required i
a rather complicated process and re
quireS that the figure representing TN
height pumped be increased by tn
loss of head in feet due to friction il
rhe pipe line; the horsepower oh
tanned by this being divided by tn
efficiency of the pumping outfit ex
pressed a a decimal.
To illustrate: Assume the case o
farmer with ten acres of alfalf.
to irrigate, who has TO 90 80 fee
for water. Government reports sro'
that from 10 to 20 inches of waite
per acre is required - produce
crop by irrigation. the average bein
Ii inches. As alfalfa requires
large amount of water we will us
the maximum, namely 20 inches.
To wet the soil feet from the sur
face under ordinary conditions re
quires that alfalfa be flooded to
depth of 6 inches. We find that, a
lowing "a hours for the irrigatin
period to irrigate 100 acres. it WI
require pump, operated by a
horsepower engine, throwing l,2O
gallons per minute.