Irrigation Water Pumps
AE-1057, April 1993
Thomas F. Scherer, Extension Agricultural Engineer
Introduction
Basic Pump Operating Characteristics
Pump Power Requirements
Centrifugal Pumps
Deep Well Turbine Pumps
Submersible Pumps
Propeller Pumps
Pump Selection Criteria
Factors to Consider in Selecting an Irrigation Pump
The heart of most irrigation systems is a pump. To make an irrigation
system as efficient as possible, the pump must be selected to match the requirements of
the water source, the water piping system and the irrigation equipment.
Pumps used for irrigation include centrifugal, deep well turbine, submersible and
propeller pumps. Actually, turbine, submersible and propeller pumps are special forms of a
centrifugal pump. However, their names are common in the industry. In this circular the
term centrifugal pump will refer to any pump located above the water surface and using a
suction pipe.
Before selecting an irrigation pump, a careful and complete inventory of the conditions
under which the pump will operate must take place. The inventory must include:
- The source of water (well, river, pond, etc.)
- The required pumping flow rate
- The total suction head
- The total dynamic head
There usually is no choice when it comes to the source of the water; it is either
surface water or well water and availability will be determined by the local geology and
hydrologic conditions. However, the flow rate and total dynamic head will be determined by
the type of irrigation system, the distance from the water source and the size of the
piping system.
Basic Pump Operating Characteristics
"Head" is a term commonly used with pumps. Head refers to the height of a
vertical column of water. Pressure and head are interchangeable concepts in irrigation,
because a column of water 2.31 feet high is equivalent to 1 pound per square inch (PSI) of
pressure. The total head of a pump is composed of several types of head that help define
the pump's operating characteristics.
Total Dynamic Head
The total dynamic head of a pump is the sum of the total static head, the pressure
head, the friction head, and the velocity head. An explanation of these terms is given
below and graphically shown in Figure 1.
Figure 1. The Total Dynamic Head (TDH) is the sum of
the total static head, the total friction head and the pressure head. The components of
the total static head for a surface water and well wate pumping system are shown.
(16KB b&w diagram)
Total Static Head
The total static head is the total vertical distance the pump must lift the water. When
pumping from a well, it would be the distance from the pumping water level in the well to
the ground surface plus the vertical distance the water is lifted from the ground surface
to the discharge point. When pumping from an open water surface it would be the total
vertical distance from the water surface to the discharge point.
Pressure Head
Sprinkler and drip irrigation systems require pressure to operate. Center pivot systems
require a certain pressure at the pivot point to distribute the water properly. The
pressure head at any point where a pressure gage is located can be converted from pounds
per square inch (PSI) to feet of head by multiplying by 2.31. For example, 20 PSI is equal
to 20 times 2.31 or 46.2 feet of head. Most city water systems operate at 50 to 60 PSI,
which, as illustrated in Table 1, explains why the centers of most city water towers are
about 130 feet above the ground.
Table 1. Pounds per square inch (PSI)
and equivalent head in feet of water.
------------------------------------------
PSI Head (feet)
------------------------------------------
0 0
5 11.5
10 23.1
15 34.6
20 46.2
25 57.7
30 69.3
35 80.8
40 92.4
45 104
50 115
55 127
60 138
65 150
70 162
75 173
80 185
85 196
90 208
95 219
100 231
------------------------------------------
Friction Head
Friction head is the energy loss or pressure decrease due to friction when water flows
through pipe networks. The velocity of the water has a significant effect on friction
loss. Loss of head due to friction occurs when water flows through straight pipe sections,
fittings, valves, around corners, and where pipes increase or decrease in size. Values for
these losses can be calculated or obtained from friction loss tables. The friction head
for a piping system is the sum of all the friction losses.
Velocity Head
Velocity head is the energy of the water due to its velocity. This is a very small amount
of energy and is usually negligible when computing losses in an irrigation system.
Suction Head
A pump operating above a water surface is working with a suction head. The suction head
includes not only the vertical suction lift, but also the friction losses through the
pipe, elbows, foot valves and other fittings on the suction side of the pump. There is an
allowable limit to the suction head on a pump and the net positive suction head (NPSH) of
a pump sets that limit.
The theoretical maximum height that water can be lifted using suction is 33 feet.
Through controlled laboratory tests, manufacturers determine the NPSH curve for their
pumps. The NPSH curve will increase with increasing flow rate through the pump. At a
certain flow rate, the NPSH is subtracted from 33 feet to determine the maximum suction
head at which that pump will operate. For example, if a pump requires a minimum NPSH of 20
feet the pump would have a maximum suction head of 13 feet. Due to suction pipeline
friction losses, a pump rated for a maximum suction head of 13 feet may effectively lift
water only 10 feet. To minimize the suction pipeline friction losses, the suction pipe
should have a larger diameter than the discharge pipe.
Operating a pump with suction lift greater than it was designed for, or under
conditions with excessive vacuum at some point in the impeller, may cause cavitation.
Cavitation is the implosion of bubbles of air and water vapor and makes a very distinct
noise like gravel in the pump. The implosion of numerous bubbles will eat away at an
impeller and it eventually will be filled with holes.
The power added to water as it moves through a pump can be calculated with the
following formula:
Q x TDH
WHP = ----------- (1)
3960
where:
WHP = Water Horse Power
Q = Flow rate in gallons per minute (GPM)
TDH = Total Dynamic Head (feet)
However, the actual power required to run a pump will be higher than this because pumps
and drives are not 100 percent efficient. The horsepower required at the pump shaft to
pump a specified flow rate against a specified TDH is the Brake Horsepower (BHP)
which is calculated with the following formula:
WHP
BHP = ---------------------- (2)
Pump Eff. x Drive Eff.
BHP -- Brake Horsepower (continuous horsepower rating of the power unit).
Pump Eff. -- Efficiency of the pump usually read from a pump curve and having a
value between 0 and 1.
Drive Eff. -- Efficiency of the drive unit between the power source and the
pump. For direct connection this value is 1, for right angle drives the value is 0.95 and
for belt drives it can vary from 0.7 to 0.85.
Effect of Speed Change on Pump Performance
The performance of a pump varies with the speed at which the impeller rotates. Theoretically,
varying the pump speed will result in changes in flow rate, TDH and BHP according to the
following formulas:
RPM2
(-----) x GPM1 = GPM2 (3)
RPM1
RPM2
(-----)2 X TDH1 = TDH2 (4)
RPM1
RPM2
(-----)3 x BPH1 = BPH2 (5)
RPM1
where:
RPM1 = Initial revolutions per minute setting
RPM2 = New revolutions per minute setting
GPM = Gallons per Minute
(subscripts same as for RPM)
TDH = Total Dynamic Head
(subscripts same as for RPM)
BHP = Brake Horsepower
(subscripts same as for RPM)
As an example, if the RPM are increased by 50 percent, the flow rate will increase by 50
percent, the TDH will increase (1.5 � 1)2 or 2.25 times, and the required BHP
will increase (1.5 � 1)3 or 3.38 times that required at the lower speed. It is
easy to see that with a speed increase the BHP requirements of a pump will increase at a faster
rate than the head and flow rate changes.
Pump Efficiency
Manufacturers determine by tests the operating characteristics of their pumps and
publish the results in pump performance charts commonly called "pump curves." A
typical pump curve is shown in Figure 2.
Figure 2. A typical pump curve for a horizontal
centrifugal pump. NPSH is the Net Positive Suction Head required by the pump and TDSL is
the Total Dynamic Suction Lift available (both at sea level).
(40KB b&w graph)
All pump curves are plotted with the flow rate on the horizontal axis and the TDH on
the vertical axis. The curves in Figure 2 are for a centrifugal pump tested at different
RPM.
Each curve indicates the GPM versus TDH relationship at the tested RPM. In addition,
pump efficiency lines have been added and wherever the efficiency line crosses the pump
curve lines that number is what the efficiency is at that point. Brake horsepower
(BHP) curves have also been added; they slant down from left to right. The BHP curves are
calculated using the values from the efficiency lines. At the top of the chart is an NPSH
curve with its scale on the right side of the chart.
Reading a Pump Curve
When the desired flow rate and TDH are known, these curves are used to select a pump.
The pump curve shows that a pump will operate over a wide range of conditions. However, it
will operate at peak efficiency only in a narrow range of flow rate and TDH.
As an example of how a pump characteristic curve is used, let's use the pump curve in
Figure 2 to determine the horsepower and efficiency of this pump at a discharge of 900
gallons per minute (GPM) and 120 feet of TDH.
Solution: Follow the dashed vertical line from 900 GPM until it crosses the
dashed horizontal line from the 120 feet of TDH. At this point the pump is running at a
peak efficiency just below 72 percent, at a speed of 1600 RPM. If you look at the BHP
curves, this pump requires just less than 40 BHP on the input shaft. A more accurate
estimate of BHP can be calculated with equations 1 and 2. Using equation 1, the WHP would
be [900 x 120] / 3960 or 27.3, and from equation 2 the BHP would be 27.3 / 0.72 or 37.9,
assuming the drive efficiency is 100 percent. The NPSH curve was used to calculate the
Total Dynamic Suction Lift (TDSL) markers at the bottom of the chart. Notice that the TDSL
at 1400 GPM is 10 feet, but at 900 GPM the TDSL is over 25 feet.
Changing Pump Speed
In addition, suppose this pump is connected to a diesel engine. By varying the RPM of
the engine we can vary the flow rate, the TDH and the BHP requirements of this pump. As an
example, let's change the speed of the engine from 1600 RPM to 1700 RPM. What effect does
this have on the GPM, TDH and BHP of the pump?
Solution: We will use equations 3, 4 and 5 to calculate the change. Using
equation 3, the change in GPM would be (1700/1600) x 900, which equals 956 GPM. Using
equation 4, the change in TDH would be (1700/1600)2 x 120, which equals 135.5
feet of TDH. Using equation 5, the change in BHP would be (1700/1600)3 x 37.9,
which equals 45.5 BHP. This point is plotted on Figure 2 as the circle with the dot in the
middle. Note that the new operating point is up and to the right of the old point and that
the efficiency of the pump has remained the same.
When a pump has been selected for an irrigation installation, a copy of the pump curve
should be provided by the installer. In addition, if the impeller(s) was trimmed, this
information should also be provided. This information will be valuable in the future,
especially if repairs have to be made.
Centrifugal pumps are used to pump from reservoirs, lakes, streams and shallow wells.
They are also used as booster pumps in irrigation pipelines. All centrifugal pumps must be
completely filled with water or "primed" before they can operate. The suction
line as well as the pump have to be filled with water and free of air. Air tight joints
and connections are extremely important on the suction pipe. Priming a pump can be done by
hand operated vacuum pumps, internal combustion engine vacuum, motor powered vacuum pumps
or small water pumps that fill the pump and suction pipe with water.
Centrifugal pumps are designed for either horizontal or vertical operation. The
horizontal centrifugal has a vertical impeller connected to a horizontal drive shaft as
shown in Figure 3. Horizontal centrifugal pumps are the most common in irrigation systems.
They are generally less costly, require less maintenance, easier to install and more
accessible for inspection and maintenance than a vertical centrifugal. There are
self-priming horizontal centrifugal pumps, but they are special purpose pumps and not
normally used with irrigation systems.
Figure 3. A horizontal centrifugal pump.
(5KB b&w diagram)
Vertical centrifugal pumps may be mounted so the impeller is under water at all times.
This makes priming unnecessary, which makes the vertical centrifugal desirable for
floating applications. Also, a self priming feature is very desirable in areas where there
are frequent electrical power outages or off-peak electrical price reductions are
available. Self priming also lends itself to the new control panels for center pivots
where automatic restart is a programmable function. A note of caution: because the
bearings are constantly under water, a higher level of maintenance may be required.
Deep well turbine pumps are adapted for use in cased wells or where the water surface
is below the practical limits of a centrifugal pump. Turbine pumps are also used with
surface water systems. Since the intake for the turbine pump is continuously under water,
priming is not a concern. Turbine pump efficiencies are comparable to or greater than most
centrifugal pumps. They are usually more expensive than centrifugal pumps and more
difficult to inspect and repair.
The turbine pump has three main parts: (1) the head assembly, (2) the shaft and column
assembly and (3) the pump bowl assembly as shown in Figure 4. The head is normally cast
iron and designed to be installed on a foundation. It supports the column, shaft and bowl
assemblies and provides a discharge for the water. It also will support either an electric
motor, a right angle gear drive or a belt drive.
Figure 4. A deep well turbine pump.
(7KB b&w diagram)
The shaft and column assembly provides a connection between the head and pump bowls.
The line shaft transfers the power from the motor to the impellers and the column carries
the water to the surface. The line shaft on a turbine pump may be either water lubricated
or oil lubricated.
The oil-lubricated pump has an enclosed shaft into which oil drips, lubricating the
bearings. The water-lubricated pump has an open shaft. The bearings are lubricated by the
pumped water. If there is a possibility of fine sand being pumped, select the oil
lubricated pump because it will keep the sand out of the bearings. If the water is for
domestic or livestock use, it must be free of oil and a water-lubricated pump must be
used. In some states, such as Minnesota, there is no choice; water-lubricated pumps are
required in all new irrigation wells.
Line shaft bearings are commonly placed on 10-foot centers for water-lubricated pumps
operating at speeds under 2,200 RPM and at 5-foot centers for pumps operating at higher
speeds. Oil-lubricated bearings are commonly placed on 5-foot centers.
A pump bowl encloses the impeller. Due to its limited diameter, each impeller develops
a relatively low head. In most deep well turbine installations several bowls are stacked
in series one above the other. This is called staging. A four-stage bowl assembly contains
four impellers all attached to a common shaft and will operate at four times the discharge
head of a single-stage pump.
Impellers used in turbine pumps may be either semi-open or enclosed as shown in Figure
5. The vanes on semi-open impellers are open on the bottom and they rotate with a close
tolerance to the bottom of the pump bowl. The tolerance is critical and must be adjusted
when the pump is new. During the initial break-in period the line shaft couplings will
tighten, therefore, after about 100 hours of operation, the impeller adjustments should be
checked. After break-in, the tolerance must be checked and adjusted every three to five
years or more often if pumping sand.
Figure 5. Both enclosed and semi-open impellers are
used in vertical turbine and centrifugal pumps. Only enclosed impellers are used in
submersible pumps.
(8KB b&w diagram)
Both types of impellers may cause inefficient pump operation if they are not properly
adjusted. Mechanical damage will result if the semi-open impellers are set too low and the
vanes rub against the bottom of the bowls. The adjustment of enclosed impellers is not as
critical; however, they must still be checked and adjusted.
Impeller adjustments are made by tightening or loosening a nut on the top of the head
assembly. Impeller adjustments are normally made by lowering the impellers to the bottom
of the bowls and adjusting them upward. The amount of upward adjustment is determined by
how much the line shaft will stretch during pumping. The adjustment must be made based on
the lowest possible pumping level in the well. The proper adjustment procedure if often
provided by the pump manufacturer. The adjustment procedure for many of the common deep
well turbine brands is outlined in Nebraska Cooperative Extension Service bulletin EC
81-760, entitled "How to adjust vertical turbine pumps for maximum efficiency."
Operating Characteristics
The operating characteristics of deep well turbine pumps are determined by test and
depend largely on the bowl design, impeller type and the speed of the impeller shaft. Flow
rate, TDH, BHP, efficiency, and RPM are similar to those given for centrifugal pumps.
Vertical turbine pumps are generally designed for a specific RPM setting.
A vertical turbine pump curve is shown in Figure 6. This pump curve is similar to the
centrifugal pump curve except instead of curves for various RPM's, the curves are for
different diameter impellers. Decreasing the diameter of impellers is called
"trimming." Manufacturers will trim impellers to the proper size to match the
TDH and flow rate requirements of a specific irrigation installation. Pump curves for
turbine pumps are normally shown for a single stage so the TDH obtained will be determined
by multiplying the indicated head on the pump curve by the number of stages. The brake
horsepower requirements must also be multiplied by the number of stages. Note that the
flow rate will not change no matter how many stages are added.
Figure 6. Deep well turbine pump curve. The brake
horsepower and total head are for one stage. If the pump had five stages, multiply the
brake horsepower and the total head values by five. The gallons per minute will stay the
same no matter how many stages are added.
(27KB b&w diagram)
Using the Pump Curve
As an example, suppose the pump curve in Figure 6 is for a 5-stage pump, with a 7.13
inch impeller supplying 800 GPM. What would be the TDH and BHP values?
Solution: Follow the dashed vertical line from 800 GPM up to where it meets the
7.13-inch impeller curve on the upper portion of the chart. Follow the dashed horizontal
line left to where it shows 26 feet of TDH. Multiplying 26 by 5 gives 130 feet of TDH.
Next, follow the dashed vertical line from 800 GPM up to the 7.13-inch impeller BHP curve
on the lower portion of the chart and then follow the horizontal dashed line left to where
it shows 6.5 BHP. Multiplying 6.5 BHP by 5 stages produces a 32.5 BHP requirement for this
pump. Also note that the pump is operating at its peak efficiency of 80 percent. At this
efficiency the calculated BHP (equations 1 and 2) is 32.8.
Installation of Vertical Turbine Pumps
Deep well turbine pumps must have correct alignment between the pump and the power
unit. Correct alignment is made easy by using a head assembly that matches the motor and
column/pump assembly. It is very important that the well is straight and plumb. The pump
column assembly must be vertically aligned so that no part touches the well casing.
Spacers are usually attached to the pump column to prevent the pump assembly from touching
the well casing. If the pump column does touch the well casing, vibration will wear holes
in the casing. A pump column out of vertical alignment may also cause excessive bearing
wear.
The head assembly must be mounted on a good foundation at least 12 inches above the
ground surface. A foundation of concrete (Figure 7) provides a permanent and trouble-free
installation. The foundation must be large enough to allow the head assembly to be
securely fastened. The foundation should have at least 12 inches of bearing surface on all
sides of the well. In the case of a gravel-packed well, the 12-inch clearance is
measured from the outside edge of the gravel packing.
Figure 7. Recommended concrete base with access pipe
for water level measurement and chlorination.
(15KB b&w diagram)
A well access pipe at least 1.5 inches in diameter must extend through the foundation
into the well casing. The access pipe serves two purposes. The first is to measure both
static and pumping water levels in the well and the second is to allow chlorination of the
well. A 3/4-inch diameter polyethylene tubing with the bottom end closed inserted into the
access pipe and extending to the pump level will make measuring water levels much easier.
Small holes must be drilled into the tubing to allow water to move in and out of the
tubing easily. More information on well maintenance can be found in NDSU circular AE-97,
"Operation and Maintenance of Irrigation Wells."
A submersible pump is a turbine pump close-coupled to a submersible electric motor as
shown in Figure 8. Both pump and motor are suspended in the water, thereby eliminating the
long drive shaft and bearing retainers required for a deep well turbine pump. Because the
pump is located above the motor, water enters the pump through a screen located between
the pump and motor.
Figure 8. A submersible pump installed in a well.
(10KB b&w diagram)
The submersible pump uses enclosed impellers because the shaft from the electric motor
expands when it becomes hot and pushes up on the impellers. If semi-open impellers were
used, the pump would lose efficiency. The pump curve for a submersible pump is very
similar to a deep well turbine pump.
Submersible motors are smaller in diameter and much longer than ordinary motors.
Because of their smaller diameter, they are lower efficiency motors than those used for
centrifugal or deep well turbine pumps. Submersible motors are generally referred to as
dry or wet motors. Dry motors are hermetically sealed with a high dielectric oil to
exclude water from the motor. Wet motors are open to the well water with the rotor and
bearings actually operating in the water.
If there is restricted or inadequate circulation of water past the motor, it may
overheat and burn out. Therefore, the length of riser pipe must be sufficient to keep the
bowl assembly and motor completely submerged at all times. In addition, the well casing
must be large enough to allow water to easily flow past the motor.
Small submersible pumps (under 5 horsepower) use single phase power. However, most
submersible pumps used for irrigation need three phase electrical power. Electrical wiring
from the pump to the surface must be watertight and all connections sealed. The electrical
line should be attached to the column pipe every 20 feet to prevent it from wrapping
around the column pipe. Voltage at the motor leads must be within plus or minus 10 percent
of the motor nameplate voltage. If there is a 5 percent voltage drop in the submersible
pump cable, voltage at the surface must not be less than 95 percent of rated voltage.
Because the pump is located in the well, lightning protection should be wired into the
control box. Lightning hits on wells with submersible pumps is a leading cause of pump
failures.
Submersible pumps can be selected to provide a wide range of flow rate and TDH
combinations. Submersible pumps more than 10 inches in diameter generally cost more than
comparably sized deep well turbines because the motors are more expensive.
Many manufacturers make submersible booster pumps. These pumps are usually mounted
horizontally in a pipeline. An advantage to using a submersible as a booster pump instead
of a centrifugal is noise reduction. This is a desirable attribute in residential settings
and near golf courses. Submersibles have also been used as booster pumps in the suction
lines of centrifugal pumps. This application is used in situations where the water level
will fluctuate a considerable amount over the season. Having a submersible in the suction
line will change the head at the inlet of the centrifugal pump from a suction head to a
positive head.
Propeller pumps are used for low lift, high flow rate conditions. They come in two
types, axial flow and mixed flow. The difference between the two is the type of impeller.
The axial flow pump uses an impeller that looks like a common boat motor screw and is
essentially a very low head pump. A single-stage propeller pump typically will lift water
no more than 20 feet. By adding another stage, heads from 30 to 40 feet are obtainable.
The mixed-flow pump uses either semi-open or closed impellers similar to turbine pumps.
In permanent installations, propeller pumps are mounted vertically as shown in Figure
9. For portable pumping platforms, they are mounted on trailers or they are mounted on
pontoons for use as floating intakes. Portable propeller pumps are commonly mounted in
almost horizontal positions (low angles) to allow them to pump into pipelines easily as
well as to be backed into a water source. Portable propeller pumps are commonly powered by
the power-take-off (PTO) on tractors. On many farms, propeller pumps are used to pump out
waste storage lagoons.
Figure 9. A propeller pump.
(8KB b&w diagram)
Power requirements of the propeller pump increase directly with the TDH so adequate
power must be provided to drive the pump at maximum lift. Propeller pumps are not suitable
under conditions where it is necessary to throttle the discharge to reduce the flow rate.
It is important to accurately determine the maximum TDH against which this type of pump
will operate.
Propeller pumps are not suitable for suction lift. The impeller must be submerged and
the pump operated at the proper submergence depth. The depth of submergence will vary
according to various manufacturers recommendations, but generally, the greater the
diameter of pump, the deeper the submergence. Following recommended submergence depths
will ensure that the flow rate is not reduced due to vortices. Also, failure to observe
required submergence depth may cause severe mechanical vibrations and rapid deterioration
of the propeller blades.
The selection of an irrigation water pump is based almost entirely on the relationship
between pump efficiency and the TDH the pump will provide at a specific flow rate. As
shown before, these parameters are also the basis of the pump characteristic curve. Table
2 can be used to narrow the selection of a pump type for a broad range of flow rates and
total dynamic heads. One item not included in the TDH values in Table 2 is the suction
lift. If your application needs to lift the water to the pump then a centrifugal pump will
have to be used.
Table 2. A chart showing the most desirable pump types
to use for a given range of flow rates and total
dynamic heads.
--------------------------------------------------------------
TDH (feet)
Gallons per ----------------------------------------------
Minute 50 or less 50 to 500 500 or more
--------------------------------------------------------------
0 to 300 Propeller Centrifugal Centrifugal
Centrifugal Vertical Turbine Vertical Turbine
Submersible Submersible
--------------------------------------------------------------
300 to 5000 Propeller Centrifugal Centrifugal
Vertical Turbine Vertical Turbine
Submersible Submersible
--------------------------------------------------------------
5000 or more Propeller Centrifugal Centrifugal
Vertical Turbine Vertical Turbine
Propeller
Submersible
--------------------------------------------------------------
Factors to Consider in Selecting an Irrigation Pump
-------------------------------------------------------------------
Pump Type Advantages Disadvantages
-------------------------------------------------------------------
Centrifugal 1. High efficiency over 1. Suction lift is limited.
a range of operating It needs to be within
conditions. 20 vertical feet of the
2. Easy to install. water surface.
3. Simple, economical and 2. Priming required.
adaptable to many 3. Loss of prime can damage
situations. pump.
4. Electric, internal 4. If the TDH is much lower
combustion engines or than design value, the
tractor power can be motor may overload.
used.
5. Does not overload with
increased TDH.
6. Vertical centrifugal
may be submerged and
not need priming.
-------------------------------------------------------------------
Vertical 1. Adapted for use in 1. Difficult to install,
Turbine wells. inspect, and repair.
2. Provides high TDH and 2. Higher initial cost
flow rates with high than a centrifugal pump.
efficiency. 3. To maintain high
3. Electric or internal efficiency, the impellers
combustion power can must be adjusted
be used. periodically.
4. Priming not needed. 4. Repair and maintenance
5. Can be used where is more expensive
water surface than centrifugals.
fluctuates.
-------------------------------------------------------------------
Submersible 1. Can be used in deep 1. More expensive in larger
wells. sizes than deep well
2. Priming not needed vertical turbines.
3. Can be used in crooked 2. Only electric power
wells. can be used.
4. Easy to install. 3. More susceptible to
5. Smaller diameters are lightning.
less expensive than 4. Water movement past
comparable sized motor is required.
vertical turbines.
-------------------------------------------------------------------
Propeller 1. Simple construction. 1. Not suitable for suction
2. Can pump some sand. lift.
3. Priming not needed. 2. Cannot be valved back
4. Efficient at pumping to reduce flow rate.
very large flow rates 3. Intake submergence depth
at low TDH. is very critical.
5. Electric, internal 4. Limited to low (less
combustion engine and than 75 feet) TDH.
tractor power can be
used.
6. Suitable for portable
operation.
-------------------------------------------------------------------
Additional Sources of Information
How To Adjust Vertical Turbine Pumps For Maximum Efficiency, University of
Nebraska Extension Bulletin Number EC 81-760.
Irrigation Handbook, Extension Agricultural Engineering Dept, NDSU.
Irrigation Power Unit Selection, NDSU Extension circular number AE-88.
Operation and Maintenance of Irrigation Wells, NDSU Extension circular number
AE-97.
Pumping Plant Efficiency, Extension Agricultural Engineering Dept, NDSU.
AE-1057, April 1993
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