Transcript Irrigation Pumping Systems

Irrigation Pumping
Systems
Objectives
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Identify pumps commonly used in irrigation pumping
systems
List the steps involved in selecting the proper size pump
Calculate pump pressures required for an irrigation
system
Select a pump from a sample pump curve
Describe common pump controls
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Warning:
 A number of catalogs, websites, and stores sell
pumps that they call "irrigation" pumps.
 These are typically a small centrifugal pump.
 Most of these pumps will run a single small sprinkler
head, but not a sprinkler system.
 Typically pumps that are suitable for sprinkler
systems are marketed under the label "high pressure
pump".
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Many pumps are sold with misleading performance
labels.
 Often a pump package will say on the box or the sign,
"XX GPM, XX PSI".
 Or it may say "XX GPM, XX feet of lift".
 In most cases this means one "or" the other, not one
"and" the other.
Do not buy a pump until you have designed your
irrigation system!
Types of Pumps
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Displacement Pumps
 Force the water to move by displacement
 Examples include: piston pumps, diaphragm pumps,
roller-tubes, and rotary pumps.
 These pumps are used for moving very thick liquids,
or creating very high pressures.
 They are used in fertilizer injectors, spray pumps, air
compressors, and hydraulic systems for machinery.
Types of Pumps
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Centrifugal Pumps
 Almost all irrigation pumps fall into this category.
 A centrifugal pump uses an "impeller" to spin the
water rapidly in a "casing", "chamber", or "housing"
 This spinning action moves the water through the
pump by means of centrifugal force.
 Centrifugal pumps may be "multi-stage", which
means they have more than one impeller and
casing, and the water is passed from one impeller
to another with an increase in pressure occurring
each time.
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Each impeller/casing combination is referred to as a
"stage".
All centrifugal pumps must have a "wet inlet", that is,
there must be water in both the intake (inlet) pipe and
the casing when the pump is started.
They must be "primed" before the first use.
Types of Centrifugal Pumps
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End-Suction Centrifugal Pump
 The most common type of
pump.
 Typically "close-coupled" or
mounted to an electric motor's
drive shaft and the pump case is
bolted straight into the motor so
that it looks like a single unit.
 The water typically enters the
pump through a "suction inlet"
centered on one side of the
pump, and exits at the top.
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Almost all portable pumps are end-suction
centrifugals.
This type of pump needs to be installed on a pad
above the high water level if pumping from a lake or
river.
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Submersible Pumps
 Installed completely underwater,
including the motor.
 The pump consists of an electric
motor and pump combined in a
single unit. Typically the pump will
be shaped like a long cylinder so
that it can fit down inside of a well
casing.
 Submersibles don't need to be
primed.
 They also tend to be more efficient
because they only push the water,
they don't need to suck water into
them.
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Most submersible pumps must be installed
in a special sleeve if they are not installed
in a well, and sometimes they need a
sleeve even when installed in a well.
The sleeve forces water coming into the
pump to flow over the surface of the pump
motor to keep the motor cool.
Without the sleeve the pump will burn up.
Because the power cord runs down to the
pump through the water it is very important
that it be protected from accidental
damage.
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Turbines and Jet Pumps.
 A turbine pump is basically a centrifugal pump
mounted underwater and attached by a shaft to a
motor mounted above the water.
 The shaft usually extends down the center of a large
pipe.
 The water is pumped up this pipe and exits directly
under the motor.
 Turbine pumps are very efficient and are used
primarily for larger pump applications.
 They are typically the type of pumps used on
municipal water system wells.
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The turbine pump is mounted
in a large concrete vault with
a pipe connecting it to the
lake.
The water flows by gravity
into the vault where it enters
the pump.
The pump motors are
suspended over the vault on
a frame.
A jet pump is similar to a
turbine pump but it works by
redirecting water back down
to the intake to help lift the
water.
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Booster pump
 Most pumps are used to take water from a standing
(or non-pressurized) source and move it to another
location.
 A booster pump is used to increase the water
pressure of water that is already on its way
somewhere.
 Example: If you have a sprinkler system that needs
80 PSI of pressure to operate, but the water line
coming onto your property only has 50 PSI of
pressure.
 In this case you would install a booster pump to raise
the pressure from 50 PSI up to 80 PSI for your
sprinkler system.
Pressure vs. Flow
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The performance of a pump varies depending on how
much water the pump is moving and the pressure it is
creating.
An important relationship not only because it determines
whether the pump is suitable for your irrigation system,
but also because it is these pump characteristics which
allow you to control the operation of your pump.
The primary relationship to understand is that as the
flow INCREASES, the pressure DECREASES
Standard formulas used to estimate
flow, pressure, and horsepower
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FT.HD. = HP x 2178 / GPM
GPM = HP x 2178 / FT.HD.
HP = GPM x FT.HD. / 2178
 HP is brake horsepower
 GPM is gallons per minute of flow
 FT.HD. is pressure in feet of head (PSI x 2.31 =
FT.HD.)
Note: these formulas have been simplified to assume a
pump efficiency of 55% which is a good average figure
to work with if you don't know the exact efficiency of your
pump. Pressure for pumps is always measured in feet of
head, one foot of head is equal to 0.433 pounds per
square inch.
Selecting a Pump
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Here's the basic procedure to follow if you're selecting a
pump for a new irrigation system. This is presented here
as an overview to help you see where we are going with
all of this:
1. Estimate your flow (GPM) and pressure (feet of
head) requirements and select a preliminary pump
model to use.
2. Using your preliminary pump information, create a
first draft irrigation design.
3. Once you have a first draft of your irrigation you may
be able to fine tune your pump selection based on
that design. Return to the pump selection process
and re-evaluate your pump selection. Make your
final pump selection.
4. Return once again to your irrigation design. Can it
be fine tuned to better match your final pump
selection? Make any necessary adjustments.
Pump Pressure
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First you will need to find out the "Dynamic Water
Depth" of the water in your well.
Dynamic Water Depth is the depth of the water below
the top of the well, in feet, when the pump is running.
Note that the term "draw-down" is often erroneously
used in place of Dynamic Water Depth.
 When the pump is running, the water level in the well
drops below the water table. It may drop a few inches
or more than 100 feet depending on the type of soil
(or rock) the well is drilled into.
Elevation Difference
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Figure out the elevation difference between the top of
your well and the highest point in the area to be irrigated
This may be a negative number if the well is higher than
the irrigated area.
Irrigation System Operating
Pressure
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This pressure will be calculated as part of the irrigation
design process and if you have a design already it
should be noted on the irrigation design.
If you have an existing irrigation system that you want to
add a new pump to, then you can try measuring the
water pressure with a gauge at the point where you plan
to tap the new pump into the system. This is one of
those unusual cases where you want to measure the
dynamic pressure, not the static pressure.
So when you measure the pressure make sure that one
of the irrigation system valves turned on and the
sprinklers are running
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Chances are you don't have an irrigation system yet, or
even a design. In this case you will need to make an
"educated guess".
Minimum Pressures for Irrigation Systems
Drip Irrigation =70 feet head (30 PSI)
Spray Type Sprinkler Heads =93 feet head (40 PSI)
Rotor Type Sprinkler Heads =104 feet head (45 PSI)
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To finish up your pressure requirement calculations you
add the values of the Dynamic Water Depth, elevation
head, and operating pressure head together to get the
total head required.
Example:
 You measure a Dynamic Water Depth of 25 feet in
your well.
 The irrigation system is 10 feet higher than the top of
the well. Your going to use rotor type sprinkler heads
so you select an operating pressure of 104 feet head.
 Your total head required would be 25 + 10 + 104 =
139 feet of head!
Selecting a Pump
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Pump Curves
 Graph which shows the performance characteristics
of a particular pump.
 Pump curves are created by the pump manufacturer
and the manufacturer should be able to provide you
with performance curves for the pumps you are
considering.
 Remember, there is always an inverse relationship
between pressure and flow. Higher pressures mean
lower flows. Lower pressures result in higher flows.
Pump Controls
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Most pump control circuits are designed using a relay
circuit that isolates the user from the pump voltage.
Most relays use 12 or 24 volts, a few use 120 volts.
Automating the Control Circuit
Common types include:
 Timer
 Pressure Switch
 Most well pumps are controlled this way
 A typical installation will have a pressure tank which
stores pressurized water so that the pump doesn't
cycle on and off rapidly due to pressure changes.
 The tank acts as a reservoir to stabilize the pressure
in the system.
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Irrigation Controller
 Most irrigation controllers have a pump start circuit
built into them.
 You simply connect the wires that go to the switch to
the controller pump start terminals, and the irrigation
controller will turn the pump on whenever it turns on a
valve.
 Do not hook up the controller to an existing relay
circuit.
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Flow Switch
 Sometimes used on booster pumps.
 When the switch detects flow in the pipes it turns on
the pump.
Combination of one or more of the above switches.
 A very common application is one relay controlled by
both a pressure switch and a manual override switch,
and a second relay operated by the irrigation
controller.