Title: How to buy an irrigation system
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Title: How to buy an irrigation system
Series Title: How to buy an irrigation system
Physical Description: Book
Creator: Dowling, S. E.
Publisher: Agricultural Extension Service, University of Florida
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Full Text



Circular 173


January 1958


COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Fllorida State University and United States Department of Agriculture, Cooperating
M. O. Watkins, Director








How To Buy an Irrigation System


By S. E. DOWLING
Assistant Agricultural Engineer


Fig. 1.-A good portable irrigation system enables a farmer to provide
water when and where needed.






Irrigation in Florida is not something new. There are over
850,000 acres under some type of irrigation. Irrigation of farms,
ranches and groves in Florida is being accomplished by sprink-
lers, perforated pipe, underground tile, furrow, overhead Skinner
systems and several other methods. Water to supply these sys-
tems comes from deep wells, shallow wells, farm ponds, rivers,
streams, lakes, ditches, canals and other sources. These differ-
ences in types of irrigation equipment and water supply make the
job of designing a proper and economical system a complicated
process that should be done by a person with proper training and
experience.
Florida is a humid state with an average rainfall in excess of
50 inches. Even though this rainfall is sufficient in quantity,
its distribution is poor. There is seldom a year that one or two
irrigations would not have been beneficial during the growing
seasons of our crops.


Fig. 2.-A flowing artesian well provides surface irrigation.

An irrigation system in Florida is like an insurance policy-
it always gives you protection against the limiting growth factor,
insufficient moisture. If farmers are protected against insuffi-
cient moisture at critical growth periods they can plant for opti-
mum production by using more plants per acre, more fertilizer
and more labor-saving equipment. This will insure a bumper
2







crop even though the rainfall is sufficient and no irrigation is
needed. You will be able to plant and produce more if you have
control of the moisture.
Farmers are being forced to strive for optimum production.
The question most often asked is whether the farmer can afford
to irrigate or not. There can be only one answer to this question.
When the annual cost per acre for irrigating any crop by any
method of irrigation is less than the average anticipated returns
from the irrigation of an acre of that crop, then you can afford
to irrigate.
Irrigation should be based on its ability to pay, not cost. An
irrigation system should start paying dividends immediately.
This publication is devoted to a method of determining an
economical sprinkler irrigation system. This method with slight
modification, could be applied to systems other than sprinkler,
or could be used to compare costs of two different type systems
in order to find the one most economical. A farmer must know
all the costs involved as well as the returns expected before buy-
ing an irrigation system.



















Fig. 3.-A centrifugal pump mounted on a four-wheel trailer with diesel
power unit is frequently used to pump irrigation water.

Without applying cost figures to the design of an irrigation
system, it is nearly impossible to properly design the most eco-
nomical system for an individual farm. No two irrigation sys-
tems are the same; each must be designed for the job that it







must do. An irrigation system is like a chain with many links;
it is no stronger than the weakest point.
To obtain the most economical system for an individual farm-
er, rancher or grower, the design should be based on an annual
cost per acre figure. Only after this figure has been determined
will be purchaser be in a position to know, not guess, whether
he can afford to irrigate.

TABLE 1.-SUGGESTED DEPRECIATION PERIOD FOR COMPONENTS OF AN
IRRIGATION SYSTEM.*

Component Depreciation Period
o _Years

W ell ............... .... ....... .. .......... ...................... 25
Pum p ........... ........... ..... .... ............................. 15
Power Units
D iesel ............... ............................................................ 15
L P -G as ............................................................... ......... 12
Gasoline, Tractor, Fuel, etc. .................................. 9
Air-cooled Engine, Gasoline ..................................... 4
Power Units, Electric ................................. .... ..... .. 25
Open Farm Ditches (Permanent) ............................. 20
Concrete Structures ... ..... ....... ........................... 20
Concrete Pipe System s .................. ..................... ..... 20
W ood Flumes ........ ...... .. ................... ...- ...-- .--- 8
Pipe, surface, gated ........-.......... -......... ... ....... 10
Pipe, water works class ................ ......... -- .....i-..- 40
Pipe, steel coated underground ................................... 20
Pipe, aluminum, sprinkler use ............................-.. .-- 15
Pipe, steel, coated, surface use only ............................... 10
Pipe, steel, galvanized, surface only ........................ 15
Pipe, w ood buried ........... ....................... .......... ... 20
Sprinkler heads .............. ............................... 8

From Sprinkler Irrigation Association, 1955, "Sprinkler Irrigation".
Some sources depreciate land leveling in 7 to 15 years. However, if
proper annual maintenance is practiced, merely figure interest on the level-
ing costs.
Use interest on capital invested in water right purchase.
A new depreciation schedule should be developed, based on the percent
of the total hours each component would be used each season. Its total
number of years of service could then be more closely calculated, figuring
some loss from storage. Such a schedule could be used for any area of the
United States.

The annual cost per acre for irrigating takes into considera-
tion all fixed costs such as cost of the equipment, cost of well
drilling, land leveling, if needed, surface ditches, or any other
equipment that might be needed to give you a working irrigation
system. The average life of each of these components can be
found in Table 1. After this is known along with the rate of
interest to be paid, it is then possible to look at Table 2 and ob-







tain a figure which, when multiplied by the cost of the component,
will give the annual fixed cost for this part of the system. Every
component must be figured this way with the individual fixed
cost added in order to obtain the Total Fixed Annual Cost. To
this fixed cost we must add variable costs such as labor, fuel,
repairs, maintenance and any other annual costs that apply to
the system. This total will give the Annual Cost for irrigating
and can be divided by the number of acres irrigated to give an
Annual Cost per Acre figure.

TABLE 2.-CAPITAL RECOVERY FACTOR.
To use this table, read down left column to proper number of years for
life of equipment. Then read across page until you reach rate of interest
that will have to be paid. Example-10 years @ 5% Interest-the CRF is
.1295. This figure multiplied by the cost of the equipment will give you
the annual cost, which includes interest.
Est. |
Life
Years 2 2% 3 3Y2 4 4V2 5 6

1 1.0200 1.0250 1.0300 1.0350 1.0400 1.0450 1.0500 1.0600
2 0.5151 0.5188 0.5226 0.5264 0.5302 0.5340 0.5378 0.5454
3 0.3468 0.3501 0.3535 0.3569 0.3604 0.3638 0.3672 0.3741
4 .2626 .2658 .2690 .2723 .2755 .2787 .2820 .2886
5 .2122 .2153 .2184 .2215 .2246 .2278 .2310 .2374
6 .1785 .1816 .1846 .1877 .1908 .1939 .1970 .2034
7 .1545 .1575 .1605 .1635 .1666 .1697 .1728 .1791
8 .1365 .1395 .1425 .1455 .1485 .1516 .1547 .1610
9 .1225 .1255 .1284 .1315 .1345 .1376 .1407 .1470
10 I .1113 .1143 .1172 .1202 .1233 .1264 .1295 .1359
12 | .0946 .0975 .1005 .1035 .1066 .1097 .1128 .1193
14 .0826 .0855 .0885 .0916 .0947 .0978 .1010 .1076
15 .0778 .0808 .0838 .0868 .0899 .0931 .0963 .1030
16 .0737 .0766 .0796 .0827 .0858 .0890 .0923 .0990
18 .0667 .0697 .0727 .0758 .0790 .0822 .0856 .0924
20 .0612 .0642 .0672 .0704 .0736 .0769 .0802 .0872
22 .0566 .0597 .0628 .0659 .0692 .0726 .0760 .0831
24 .0529 .0559 .0591 .0623 .0656 .0690 .0725 .0797
25 .0512 .0543 .0574 .0607 .0640 .0674 .0710 .0782
30 I .0447 .0478 .0510 .0544 .0578 .0614 .0651 .0727
35 6 .0400 .0432 .0465 .0500 .0536 .0573 .0611 .0690
40 I .0366 .0398 .0433 .0468 .0505 .0543 .0583 .0665
45 1 .0339 .0373 .0408 .0445 .0483 .0522 .0563 .0647
50 | .0318 .0353 .0389 .0426 .0466 .0506 .0548 .0634


The Annual Fixed Cost can be reduced, but this does not
necessarily mean that the annual cost per acre will be reduced;
usually the opposite occurs. The fixed cost is usually reduced
by lowering the initial investment. This can be done in several
ways, such as reducing pipe size, eliminating labor-saving and
safety features, increasing the number of sets per day, poor land
leveling, plowing furrow ditches farther apart, or some other
5






method for reducing the amount of equipment to be purchased.
Any of these reductions will decrease the initial investment but
they will also result in an increase in labor or fuel consumption
or both. This usually causes an increase in the total annual cost.
What we must find is the proper balance between labor, fuel
and equipment in order to design the most economical system to
own and operate for the individual system that is being designed.





















Fig. 4.-A centrifugal pump operating from the power take-off of a tractor
provides irrigation water.

There is no definite step-by-step procedure for designing an
irrigation system, but every designer must have certain informa-
tion, such as would be required to fill in the data sheet under
Table 3. This Data Sheet, "Farm Information", must be used
as a starting point in the design of an irrigation system.
The data sheet, Design and Specification Information (Table
3), should be filled out and supplied to the purchaser so that he
will always have a record on hand that explains the system to
him. Before this data sheet can be filled in completely it will be
necessary to use the annual cost per acre method in order to be
sure the selection of equipment is the most economical.
Most of the answers to the questions raised by this form can
be easily and correctly supplied by the irrigation engineer. How-
ever, there are a few points that should be emphasized.
6





Under System Capacity Requirements (Table 3) we have a
sub-heading, "Water Application Efficiency (Percent)." Appli-
cation efficiencies of 70 percent have been used as standards
throughout most of Florida for both close and wide spacings,
high and low pressures, and in most cases for various wind con-
ditions as well as different temperatures and humidities. This
percentage cannot be correct for all of these conditions. It is,
however, possible to determine the application efficiency on the
basis of the condition which the system is designed.


Fig. 5.-A line valve and valve opener enables the operator to change
sprinkler lines without shutting down the system.

Frost and Schwalen have prepared a nomograph for deter-
mining percent evaporation and wind drift losses from sprinkler
systems in Fig. 6. One hundred minus the percent evaporation
losses would equal the initial application efficiency. This per-
centage could be used as the efficiency for design purposes if
there were complete uniformity of distribution of the water ap-
plied. As there is something less than 100 percent uniformity
in distribution, a measure of such uniformity is needed. This is
possible and is being done at present by several sprinkler com-

(Continued on Page 11)


Lu






TABLE 3.-SPRINKLER IRRIGATION TECHNICAL DATA SHEET*, ASAE
TENTATIVE STANDARD, APPROVED JANUARY 1957.

FARM INFORMATION
Name of Owner................................... Address----- --............................... Date-.......--.
Section............ Range............ Township................ County................ State........
IRRIGATION SYSTEM DESIGN AREA:
Topography-Include profile of proposed main pipeline locations. Give ele-
vations of points around field boundaries, water level, pump locations,
highest and lowest points in design area, and natural gas or electrical
power line location.
Soils-Show predominating soil types and location on map.
Field Nos. 1 2 3 4 5


Available moisture
holding capacity
................. (in/ft.)
Intake rate
(in/hr)
Effective depth
of soil (ft)


WATER SUPPLY
Source.................... Amount available.................... GPM...............
Seasonable variation GPM-....-..................to GPM-....-.........
Delivery scheduling-.....................


acre feet


POWER SOURCE
Electrical.------.......... .................. Internal combustion engine................
Fuel Type-...............................-...... Other .... ........................
If electrical give power phase...........-Voltage............HP Limitations......
LABOR AVAILABILITY
Hours of operation per day---.....--........--Operation days per week..............
IRRIGATION REQUIREMENTS

Design Area Requirements
I I Moisture
Effective to be re- Peak Peak use
Field root zone placed moisture period
Crops No. Acres depth each irri- use rate, irrigation
feet gation, in. per frequency
inches day days



This data sheet was developed by ASAE Sprinkler Irrigation Research Committee in
cooperation with the Sprinkler Irrigation Association, U. S. Farmers' Home Administration
and U. S. Soil Conservation Service.


i


I



L~ 1







TABLE 3.-SPRINKLER IRRIGATION TECHNICAL DATA SHEET, ASAE
TENTATIVE STANDARD, APPROVED JANUARY 1957.-(Continued)

DESIGN AND SPECIFICATION INFORMATION
SYSTEM CAPACITY REQUIREMENTS
Minimum system
capacity............................gpm Field Nos. 1 2 3 4 5
Application rate (in/hr) ..........................
Time of lateral operation per set (hrs) |
Depth applied per set (inches) .............. I
Number of lateral sets per day (no.)--....I
Operation period to cover area (days). I..
System capacity required (gallons) ....
Water application efficiency (percent)..
Depth moisture replaced
each irrigation (inches) ...........--.........
SPRINKLER SELECTION
Application rate............in per hr. Sprinkler spacing on lateral..... ......ft.
Lateral spacing on mainline............ft. Sprinkler discharge................gpm
Diameter of circle covered................ft. Type......Nozzle sizes ........ x ...----
Required operating pressure..............psi
LATERAL DESIGN
Lateral spacing on mainline........ft. Sprinkler spacing on lateral-.......ft.
Lateral length...............ft. Area covered per lateral setting............acres.
No. sprinklers per lateral....................Lateral discharge...................------gpm.
No. laterals required-.................. to cover design area in....................days.
Pipe size required: Length-...........ft. Diameter.... ....in. Gage pipe......
Length............ft. Diameter............in. Gage pipe......
Rise or fall (circle applicable condition) in lateral............ ..-----..- ft.
Pressure loss in lateral due to friction............psi or ..~~.- ..--------.....--ft.
Pressure required (at mainline) to operate lateral............psi or......-.....ft.
MAINLINE DESIGN
Portable------............. or Permanent......................--Material: Steel............
Aluminum....................--or Other.....--........---.....--
Mainline length........................ft. Discharge capacity ..........................gpm.
Rise or fall (circle one) in mainline...............................ft.
Allowable head loss due to friction.. -- -----............--ft.
Pipe sizes required ....................ft. of....................in pipe ..................- gage.
....--..... ..... ft. of................----- -in pipe....................gage.
................. ft. of-----....................in pipe....................gage.
Head loss due to friction............ft. Outlet spacing on mainline............ft.
SUPPLY LINE DESIGN (that portion of mainline outside design area)
Supply line length------......................ft. Discharge capacity......................gpm.
Pipe size required ...................... in. Friction head loss.. --------........................ft.
TOTAL DYNAMIC HEAD REQUIREMENTS
Pressure required at lateral ----------................... .......psi .....................- ...-ft.
Friction head loss in mainline ---...---- psi--.. ------.....................ft.
Friction head loss in supply line ............................----ft.
Friction head loss on suction line ..........................ft.
Elevation difference between pump and highest point of lateral line....ft.
Elevation difference between watersource and center of pump............ft.
Miscellaneous friction head loss in special valves and fittings............ft.
Total ................................................--------------------------. ft.







TABLE 3.-SPRINKLER IRRIGATION TECHNICAL DATA SHEET, ASAE
TENTATIVE STANDARD, APPROVED JANUARY 1957.-(Continued)


PUMP REQUIREMENTS
Capacity..........................gpm at head_.


............ft. Size ........................in.


PUMP SPECIFICATIONS
Type .......... .. ............................ capacity........................................--- -gpm
Efficiency ........................................ % at................ .................. ft. head
Rpm @ required discharge............Brake hp @ required discharge..........

POWER REQUIREMENTS


Water hp. .............. Efficiency.....

POWER UNIT SPECIFICATIONS
I


... % Brake hp............... Rpm...........


Type .................... M ake....................- M odel...................... Size.............
Continuous hp rating.-.................at ..............-...rpm.
Cu-in displacement ................Stroke................in.
Piston speed at design load............Bmep at design load-----......................psi
Type of power conversion................Speed ration.........................
Electric motor: Voltage -.............-.....- Phase...................... Rpm-...............


ECONOMIC ANALYSIS OF IRRIGATION
SYSTEM COST


I Quanti- I
ITEM I ty and
IUnit

W ell unit ......................................
Pumphouse unit ................. ..... --
Pow er unit ....................................
Pum p unit .......................................
Power line extension .................... ft.
Main pipe line (complete
with valves) .........-........-- .. -- ft.
Lateral pipe lines (complete) .... ft.
Sprinklers and risers ............ no.
Special equipment
List ...................................
Total Material Costs .....--......
Cash outlay for installation .......
Farm costs, Labor ......................
Tractor use .........-__
Other ................ I
Total Farm Costs .............. --
Total Cost ...............................


Unit Total
cost, cost,
dollars dollars


Annual
Fixed
cost


I I I


LABOR COSTS
Moving laterals (per irrigation) ...............................hrs.
Moving mainline (per irrigation) ......................-...hrs.
Starting and stopping pump (per irrigation) ..................hrs.
Other time required (per irrigation) ....................-..hrs.
Total labor (per irrigation) .......................hrs. @ $................ per hour -....
Seasonal cost = Cost per irrigation.......... x No. of irrigations..............
10







TABLE 3.-SPRINKLER IRRIGATION TECHNICAL DATA SHEET, ASAE
TENTATIVE STANDARD, APPROVED JANUARY 1957.-(Continued)

INVESTMENT COST
Water development....(well, pond, sump, etc.) ........$--
Land development....(leveling, clearing) .................----
Equipment ...................................... ................. ---
M materials .......................................................................... --
L abor .............................. ................................
Other....(rights of way, legal and technical costs)....
Total investment ................................... .. --------
ANNUAL FIXED COSTS
Annual depreciation of investment ............................$--
Interest on average investment .............................. --
Taxes....(irrigation equipment) ..................................-------
Insurance ...............---- ..............-..-------..------------
Total fixed cost ....................-- ---- ...............---- -- ------
ANNUAL OPERATING AND MAINTENANCE COST
Hours of operation per year
Fuel or electricity -----......- ......---- ----...----$-
Lubricating oils, grease, attendance ..........................--
Labor, irrigating ...----.................................. ----- ----
Maintenance irrigation system ..................................
Total operating and maintenance costs .............................. $--
Total cost of irrigation = Fixed cost plus operating and
m maintenance costs ....................... ....................................... $
Cost per acre inch = Total cost of irrigation divided by
total acre inches applied .............. ........................ $--
Cost per irrigated acre = Cost per acre inch mulitplied
by inches applied .............----------------- -- --
Remarks: --.. -----..--------------------------

Title --------- ---................................
Title .
D ate ........... .... ....... ...............
(Continued from Page 7)
panies. The formula being used by these companies to find the
uniformity coefficient, CU, of a given sprinkler head is:

c = 100 1.0 )
u MN
Where x = deviation of individual observation from the mean value M.
N = number of observations.

Another formula, identical to the uniformity coefficient formu-
la above, has been proposed by Vaughn E. Hansen, professor of
irrigation and drainage engineering, Utah State University.
This Water Distribution Efficiency formula is as follows:

W.D.E. 100 (1 average deviation
average depth applied

or E = 100 1 -
d D








PERCENT RELATIVE HUMIDITY
- s8


I I iI Ir-II- I\
0 o ol| O O .-
o a DC I i. E o O

VAPOR-PRESSURE DEFICIT IN LBS. PER SO. IN.


PIVOT


PIVOTT
-l7--


I
NOZZLE DIAMETER IN 64TH INCHES




0 -

PERCENT EVAPORATION LOSS
I
/


NOZZLE PRESSURE IN ,LBS.
I I .: CA
i i i I 1 i


PIVOT


PER SQ. IN.

I I I



PIVOT
-------- o


WIND VELOCITY IN MILES PER HOUR
I I I I I I







Where E = water distribution efficiency
d
y = average numerical deviation in depth of water stored from
average depth stored during the irrigation
d = average depth of water stored during the irrigation

The product of the water distribution efficiency and the initial
application efficiency would give the overall application efficiency
by which a system could be designed.
After considering the uniformity of the sprinklers and other
factors, such as the intake rate of the soil and evaporation and
wind drift losses, the design engineer can select the proper
sprinkler and spacings for the system to be designed.


Fig. 7.-A perforated pipe lateral line. In Florida this type of irrigation
is used mainly in groves.

The size of the lateral line is determined by the fact that it
is not economical for the loss in pressure to be more than 20%
of the operating pressure at the sprinkler head. For example,
if the sprinkler is to operate at 50 PSI, then the allowable fric-
tion loss between the first and last sprinkler on a given lateral
should not be over 10 PSI. If the friction loss is greater than
this allowable 20%, the size lateral line must be increased, or at
least enough larger size pipe used to reduce the friction loss total
13






in the lateral to an amount that is less than the allowable 20%
or the 10 PSI in the example.
Ordinarily on short laterals of 660 feet or less, having two
sizes of pipe presents a handicap in moving and keeping the
sizes separate. For this reason sprinkler lines are normally over
660 feet in length before it is economical to have two different
size pipes in the line. Always remember that the smaller'the
loss the more uniform the application.


Fig. 8.-A tee valve on the main line.


One of the methods that should be emphasized is that of se-
lecting the most economical size mainline. It is possible to pump
a given amount of water through nearly any size mainline if the
pump has sufficient capacity and is powered by a sufficiently large
power unit. The smaller the pipe, the lower the initial cost;
however, a larger pumping plant and more fuel will be required
to operate the equipment for the entire life of the system.
The following (Example I) shows a method for determining
the most economical size mainline for given conditions. All
these conditions have a bearing on the selection of the size main-
line and a change in any one of the stated conditions could pos-
sibly change the size mainline which would be most economical.
14







EXAMPLE I
MAINLINE SELECTION
Assuming 1320 feet of mainline is needed, with 350 G.P.M. for 600 hours,
the following procedure could be used.
FRICTION VALUES OF PIPE WITH COUPLERS AT 350 G.P.M. (1)
4" 5" 6" 7" 8"
350 G.P.M. Loss in Feet
per 100 Feet of Pipe ............ 8.5' 2.79' 1.20' 0.58' 0.28'
350 G.P.M. Loss in Feet
per 1320 Feet of Pipe ............ 114.6' 36.8' 15.8' 7.65' 3.7'
(350 G.P.M.) (1 TDH)
BHP = = .126 HP per Foot of Head @ 70% Eff.
3960 x (0.70) Eff
Assuming electricity to be used @ 0.93 HP hrs. per kilowatt (2) then
4" 5" 6" 7" 8"
BHP for 350 G.P.M.
@ 1320 Ft. Pipe ....................... 14.44 4.64 1.99 .96 .47
Kilowatts per Hour
HP 0.93 ............................. 15.5 5 2.14 1.03 .5
Cost @ 24/kilowatt hr. ............ .31 .10 .0428 .0206 .01
Cost /600 hours ........................ $186.00 $60.00 $25.68 $12.36 $6.00
Cost of 1320 feet mainline........$1099.56 $1544.40 $2204.40 $3022.80 $3828.00
Annual Fixed Cost -
using Capital Recovery
Factor .0963 ................. $105.89 $148.73 $212.28 $291.10 $368.64
Total Annual Cost .................... $291.89 $208.73 $237.96 $303.46 $374.64

The break even point between any two adjacent sizes of pipe figured in terms
of hours can be determined as follows:
Cost per Year of Cost per Year of
Larger Pipe Smaller Pipe
Break even point
Fuel Cost per Hour Fuel Cost per Hour
of Smaller Pipe of Larger Pipe
Break even point $148.73 $105.89 $42.84
--- --- 204 hrs.
between 4" & 5" $ .31- $ .10 $ .21
Break even point $212.28 $148.73 $63.55
= = 1111 hrs.
between 5" & 6" $ .10 $ .0428 $ .0572
(1) See Table 4, Loss of Head in Feet per 100 Ft.
(2) See Table 5, Brake Horsepower Hours/Unit of Fuel.

The result of the mainline selection example is that for the
conditions stated the proper and most economical size mainline is
5 inches. However, if all conditions remained the same except
the number of hours operation, the following results will be ob-
served: for less than 204 hours operation a 4-inch pipe will be
most economical, whereas for over 1111 hours operation a 6 inch
pipe will be most economical.
The second method that needs to be emphasized is selection
of the Power Unit. It is impossible to over-emphasize the im-









TABLE 4.-Loss OF HEAD IN FEET PER 100 FEET OF ALUMINUM TUBING WITH COUPLERS.*
Based on Scobey's Formula with Ks = 0.40


FLOW
Gallons Cubic Feet
per per 2"OD
Minute Second

10 0.02 0.32
50 0.11 6.70
100 0.22 21.6
120 0.27
140 0.31
160 0.35
180 0.40
200 0.44
220 0.49
240 0.53
260 0.58
280 0.62
300 0.67
350 0.77
400 0.89
450 1.00
500 1.11
550 1.22
600 1.33
650 1.45


3"OD


0.05
0.90
3.21
4.81
6.01
7.81
9.40
11.82
13.3
15.7
18.3
21.1
23.9


NOMINAL SIZE

4"OD 5"OD 6"OD 7"OD
I


0.81
1.20
1.48
1.97
2.31
3.01
3.51
4.09
4.89
5.80
6.61
8.50
10.21
12.5
15.3
18.6
21.8
25.3


0.28
0.39
0.51
0.67
0.83
1.02
1.20
1.41
1.64
1.94
2.24
2.79
3.69
4.46
5.20
6.09
7.60
8.98


8"OD


10"OD I 12"OD









TABLE 4.-Loss OF HEAD IN FEET PER 100 FEET OF ALUMINUM TUBING WITH COUPLERS.*
Based on Scobey's Formula with K, = 0.40

FLOW NOMINAL SIZE
Gallons Cubic Feet
per per 2"OD 3"OD 4"OD 5"OD 6"OD 7"OD 8"OD 10"OD 12"OD
Minute Second

700 1.56 10.52 4.13 1.89 1.04 0.35 0.14
750 1.67 11.1 4.59 2.15 1.13 0.39 0.16
800 1.78 12.5 5.29 2.40 1.27 0.42 0.18
850 1.89 13.9 5.80 2.71 1.41 0.46 0.21
900 2.00 15.7 6.59 3.05 1.57 0.53 0.22
950 2.11 17.3 7.25 3.35 1.76 0.58 0.23
1000 2.22 19.1 7.95 3.69 1.89 0.65 0.28
1100 2.45 22.9 9.19 4.59 2.31 0.79 0.35
1200 2.67 26.9 11.52 5.41 2.72 0.95 0.39
1300 2.89 12.6 6.79 3.40 1.11 0.46
1400 3.12 14.7 7.30 3.79 1.25 0.53
1500 3.33 16.7 8.50 4.29 1.41 0.60
1600 3.56 18.8 9.28 4.90 1.60 0.67
1700 3.78 21.0 10.20 5.41 1.81 0.74
1800 4.00 23.06 11.01 6.01 2.01 0.83
1900 4.22 12.4 6.70 2.19 0.90
2000 4.45 13.7 7.30 2.35 0.99
2500 5.56 3.91 1.59
3000 6.68 _______2.23

* Sehrunk, John F., Design Handbook, Irrigation Equipment Company, Eugene, Oregon.






portance of proper selection of the pumping plant. The type
pump curve should be carefully determined by such factors as
the water supply and the operational procedure that is to be
followed. Fluctuating water levels may make it desirable to
select a pump that will maintain a rather constant flow under
varying head conditions. However, if the operator plans to shut
down a portion of the system (one lateral) while moves are
being made, then a pump would need to be selected which would
maintain a more constant head under varying flow changes.
It is of vital importance to consider the pumping and power
units both separately and together. The designer should always
keep in mind the importance of selecting a pump to operate at
a high efficiency, as a cheaper pump operating at a lower effi-
ciency may result in a much higher total annual cost than a
higher priced pump which operates at a higher efficiency.


- .


.. '_X-u -


Fig. 9.-An electric turbine pump provides water for irrigation.

In considering the power source, the brake horsepower re-
quired must be available for continuous duty. For electric mo-
tors the actual horsepower needed is sufficient, while for internal
combustion engines the bare engine horsepower given for most
units is a theoretical horsepower at the maximum r.p.m. and is
18







not a usable horsepower. Therefore, the selected power unit
must have sufficient horsepower to compensate for the following
deductions and still have the required brake horsepower left at
the desired r.p.m.

TABLE 5.-PERFORMANCE OF IRRIGATION PUMPING UNITS
BRAKE HORSEPOWER HOURS/UNIT OF FUEL (1).

FUEL Fuel Consumption in BHP Hrs./Gallon
Average of Tests I Range |Maximum Possible

Diesel ............ ... 11.2 15.2 -6.1 15.2
Gasoline ............... 6.9 9.45-6.0 11.2
Tractor Fuel ........ 7.2 9.5 -4.8 11.1
Propane .............. .7 7.6 -3.9 8.7
Natural Gas* ..... 5.4* 5.7 -5.2* 8.3*
Electric** ............ 0.93** 1.15-0.55** 1.20**

* BHP Hours per 100 cubic feet of gas.
** BHP Hours per kw.

As an example, consider an engine that has a bare engine
horsepower of 148 at 2400 r.p.m. First, find what the horsepower
is at 1800 r.p.m., the speed desired for this example. This engine
has only 117 bare engine horsepower at this speed. The follow-
ing deductions need to be made in order to find the horsepower
of this engine that is available for continuous duty at 1800 r.p.m.
Deduct 31/2% for each 1000 ft. rise above sea level; deduct 1%
for each 100 rise in temperature above 600 F.; deduct 10% for
fan, belts, etc.; and deduct 20% for continuous duty. Therefore,
if the unit were operating at sea level with an average tempera-
ture of 90 F., the following deduction would be necessary:

Fig. 10.-A large gun-type sprinkler throws water over a considerable area.







300 temperature rise ...---.. 3%
Fan and accessories -... 10%
Continuous duty .......-- .....--. 20%

33%
117 HP minus 33% = 78.39 available for continuous duty.
In considering this example it is very easy to understand why
so many units are under-designed in the case of power. This
unit in the example would have been called a 148 HP engine,
while actually it developed for the purpose to be used only 78 HP.
This is the reason why it is usually bad to purchase a used auto-
mobile engine for irrigation purposes.
In Example II a method of proper power unit determination
is given.
EXAMPLE II

POWER UNIT DETERMINATION
Using as an example a power requirement of 40 horsepower
at 1750 r.p.m., and assuming that there will be an operating loss
3% per 1000 ft. elevation above sea level, and 1% per 100 F.
above 600 F., 20% for continuous operation and 10% for fan and
accessories, and further assuming that these factors and the,
site resulted in the need for 65 HP diesel, LP gas or gasoline
engine, at 1750 r.p.m. The Power Unit will operate an average
of 600 hrs/year. The following comparison can now be made:


Electric
B.h.p. required .............. 40
Average life, years ........ 25
Capital-recovery factor
@ 5% Int. ................ ...... 0.0710
Approx. purchase price-
(less pump)-includes all
motor & engine accesso-
ries ............................. ... $1500.00
Annual fixed cost.............. $ 106.50
Average fuel consump-
tion in b.h.p. hrs/gallon
or per KW ......................... 0.93
Fuel consumption per hr. 43 KW
Fuel consumption for
600 hrs. of use .................. 25,800 KW
Cost per unit of fuel ........ .02%2
Cost per 600 hrs. of fuel.. $ 645.00
Elect. minimum charge
12.00/year/HP ................ 480.00
Maintenance ................. 15.00
Other cost-oils, etc. .... ---
Total annual cost ............ $ 766.50


Diesel
65
15

0.0963


LP Gas
65
12


Gasoline
65
9


0.1128 0.1407


$2400.00 $1380.00 $1250.00
$ 231.12 $ 155.66 $ 175.88

11.2 5.7 6.9
3.58 Gals. 7.0 Gals. 5.8 Gals.


2,148 Gals.
.16
$ 343.68

None
100.00
25.00
$ 699.80


4,200 Gals.
.16
$ 672.00

None
50.00
25.00
$ 902.66


3,480 Gals.
.22
$ 765.60

None
70.00
25.00
$1036.48







As can be observed for the conditions and rates in Example
II, diesel power is the most economical.
The minimum electrical rate did not apply, since the electric
bill was in excess of the minimum. Any one of the conditions
could be changed and, therefore, possibly change the outcome in
favor of one of the other three sources of power.
After having found the proper and most economical compon-
ents of the system, it will be possible to find the Annual Cost per
acre for the system.
A method for determining this annual cost per acre is offered
in Example III.
EXAMPLE III
ANNUAL COST PER ACRE
Assuming 40 acres of vegetables with a well in the center
of the acreage and that all selections of equipment have been
determined as follows:
Cost of sprinkler heads ...................................... $198.00
Life of sprinkler heads ........-.........-- ................. 8 years
Capital recovery factor @ 5% Int. .................... .1547
Annual cost of sprinkler heads .......................... $ 30.62
Cost of main & lateral lines & fittings ............ 1700.00
Life of main & lateral lines ................................ 15 years
Capital recovery factor @ 5% Int. .............. .0963
Annual cost of main & lateral lines ............... 163.71
Cost of turbine pump ........................................ 2000.00
Life of turbine pump ......................................... 15 years
Capital recovery factor @ 5% Int. .........---.... .0963
Annual cost of turbine pump ............................ 192.60
Cost of power unit-LP gas .......-....................-. 1100.00
Life of LP gas engine ........................................ 12 years
Capital recovery factor @ 5% Int. .................. .1128
Annual cost of power unit .................................. 124.08
Cost of w ell ............................................................ 1000.00
Life of w ell .................................................. 25 years
Capital recovery factor @ 5% Int. ......-........ .0710
Annual cost of well .............................................. 71.00
Annual cost of fuel/600 hrs. .......................... 384.00
Annual m maintenance ............................................ 50.00
Annual oil & m isc. cost ..................................... 25.00
Annual labor cost- 600 hrs. .............................. 600.00
Total annual cost ......................................... .. $1641.01
Total annual cost
Total annual cost per acre = --- -
No. acres irrigated
1641.01
= $41.00
40
It is now possible to examine this cost of $41.00 per acre and
decide whether irrigating this 40 acres will pay the $41.00 cost
plus some return for the investment. If the average anticipated






return per acre of vegetables is higher than $41.00 the owner
can afford to irrigate. If the returns are less than $41.00 then
he could not afford to irrigate in this situation.
The annual cost per acre could range from approximately
$10.00 to as high as $200.00. Each individual system must be
worked out before it can be accurately determined if irrigation
is profitable.
In the purchasing of an irrigation system for a farm, be sure
to do all of the following:
1. Have a responsible firm with a trained irrigation engineer
design the system.
2. Insist that the design of the system be based on an annual
cost-per-acre basis.
3. Be sure the designer furnishes a performance sheet.
4. Have a guarantee in writing that system will perform as
performance sheet states.
5. Do not always buy the lowest priced system but do pur-
chase the system having the lowest annual cost per acre.
6. Do not buy system piecemeal but do buy from one repu-
table source that is in business locally and carries a substantial
inventory of parts in stock.
7. Do not purchase any system unless sketch to scale is fur-
nished showing layout of system.
8. Have the Extension Agricultural Engineer or Soil Conser-
vation Engineer check the system design before buying, if pos-
sible.

The author is not trying to make irrigation engineers out of
those who read this publication. It is hoped, however, that the
methods involved in selection of the most practical and economi-
cal system for the individual farmer can be understood and will
make the reader conscious of the difference between good design
and poor design. It is hoped that the reader, if he should become
a purchaser, will insist that he be shown that the recommended
design is the most economical for his farm.
The author would again like to call to the reader's attention
that the cost figures in this- publication are not necessarily cor-
rect. These figures are for illustration purposes only; it is the
method of obtaining that is important.
A properly designed irrigation system will pay dividends for
the life of the equipment.




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