Irrigation Pumping Irrigation Pumping SystemsSystems

ObjectivesObjectives

Identify pumps commonly used in irrigation pumping Identify pumps commonly used in irrigation pumping systemssystems

List the steps involved in selecting the proper size pumpList the steps involved in selecting the proper size pump Calculate pump pressures required for an irrigation Calculate pump pressures required for an irrigation

systemsystem Select a pump from a sample pump curveSelect a pump from a sample pump curve Describe common pump controlsDescribe common pump controls

Warning:Warning: A number of catalogs, websites, and stores sell A number of catalogs, websites, and stores sell

pumps that they call "irrigation" pumps. pumps that they call "irrigation" pumps. These are typically a small centrifugal pump. These are typically a small centrifugal pump. Most of these pumps will run a single small sprinkler Most of these pumps will run a single small sprinkler

head, but not a sprinkler system. head, but not a sprinkler system. Typically pumps that are suitable for sprinkler Typically pumps that are suitable for sprinkler

systems are marketed under the label "high pressure systems are marketed under the label "high pressure pump".pump".

Many pumps are sold with misleading performance Many pumps are sold with misleading performance labels.labels. Often a pump package will say on the box or the sign, Often a pump package will say on the box or the sign,

"XX GPM, XX PSI". "XX GPM, XX PSI". Or it may say "XX GPM, XX feet of lift". Or it may say "XX GPM, XX feet of lift". In most cases this means one "In most cases this means one "oror" the other, not one " the other, not one

""andand" the other. " the other. Do not buy a pump until you have designed your Do not buy a pump until you have designed your

irrigation system!irrigation system!

Types of PumpsTypes of Pumps

Displacement PumpsDisplacement Pumps Force the water to move by displacement Force the water to move by displacement Examples include: piston pumps, diaphragm pumps, Examples include: piston pumps, diaphragm pumps,

roller-tubes, and rotary pumps. roller-tubes, and rotary pumps. These pumps are used for moving very thick liquids, These pumps are used for moving very thick liquids,

or creating very high pressures. or creating very high pressures. They are used in fertilizer injectors, spray pumps, air They are used in fertilizer injectors, spray pumps, air

compressors, and hydraulic systems for machinery. compressors, and hydraulic systems for machinery.

Types of PumpsTypes of Pumps

Centrifugal PumpsCentrifugal Pumps Almost all irrigation pumps fall into this category. Almost all irrigation pumps fall into this category. A centrifugal pump uses an "impeller" to spin the A centrifugal pump uses an "impeller" to spin the

water rapidly in a "casing", "chamber", or "housing" water rapidly in a "casing", "chamber", or "housing" This spinning action moves the water through the This spinning action moves the water through the

pump by means of centrifugal force. pump by means of centrifugal force. Centrifugal pumps may be "multi-stage", which Centrifugal pumps may be "multi-stage", which

means they have more than one impeller and means they have more than one impeller and casing, and the water is passed from one impeller casing, and the water is passed from one impeller to another with an increase in pressure occurring to another with an increase in pressure occurring each time. each time.

Each impeller/casing combination is referred to as a Each impeller/casing combination is referred to as a "stage". "stage".

All centrifugal pumps must have a "wet inlet", that is, All centrifugal pumps must have a "wet inlet", that is, there must be water in both the intake (inlet) pipe and there must be water in both the intake (inlet) pipe and the casing when the pump is started. the casing when the pump is started.

They must be "primed" before the first use. They must be "primed" before the first use.

Types of Centrifugal PumpsTypes of Centrifugal Pumps

End-Suction Centrifugal PumpEnd-Suction Centrifugal Pump The most common type of The most common type of

pump. pump. Typically "close-coupled" or Typically "close-coupled" or

mounted to an electric motor's mounted to an electric motor's drive shaft and the pump case is drive shaft and the pump case is bolted straight into the motor so bolted straight into the motor so that it looks like a single unit. that it looks like a single unit.

The water typically enters the The water typically enters the pump through a "suction inlet" pump through a "suction inlet" centered on one side of the centered on one side of the pump, and exits at the top. pump, and exits at the top.

Almost all portable pumps are end-suction Almost all portable pumps are end-suction centrifugals. centrifugals.

This type of pump needs to be installed on a pad This type of pump needs to be installed on a pad above the high water level if pumping from a lake or above the high water level if pumping from a lake or river. river.

Submersible PumpsSubmersible Pumps Installed completely underwater, Installed completely underwater,

including the motor. including the motor. The pump consists of an electric The pump consists of an electric

motor and pump combined in a motor and pump combined in a single unit. Typically the pump will single unit. Typically the pump will be shaped like a long cylinder so be shaped like a long cylinder so that it can fit down inside of a well that it can fit down inside of a well casing. casing.

Submersibles don't need to be Submersibles don't need to be primed. primed.

They also tend to be more efficient They also tend to be more efficient because they only push the water, because they only push the water, they don't need to suck water into they don't need to suck water into them. them.

Most submersible pumps must be installed Most submersible pumps must be installed in a special sleeve if they are not installed in a special sleeve if they are not installed in a well, and sometimes they need a in a well, and sometimes they need a sleeve even when installed in a well. sleeve even when installed in a well.

The sleeve forces water coming into the The sleeve forces water coming into the pump to flow over the surface of the pump pump to flow over the surface of the pump motor to keep the motor cool. motor to keep the motor cool.

Without the sleeve the pump will burn up. Without the sleeve the pump will burn up. Because the power cord runs down to the Because the power cord runs down to the

pump through the water it is very important pump through the water it is very important that it be protected from accidental that it be protected from accidental damage.damage.

Turbines and Jet PumpsTurbines and Jet Pumps. . A turbine pump is basically a centrifugal pump A turbine pump is basically a centrifugal pump

mounted underwater and attached by a shaft to a mounted underwater and attached by a shaft to a motor mounted above the water. motor mounted above the water.

The shaft usually extends down the center of a large The shaft usually extends down the center of a large pipe. pipe.

The water is pumped up this pipe and exits directly The water is pumped up this pipe and exits directly under the motor. under the motor.

Turbine pumps are very efficient and are used Turbine pumps are very efficient and are used primarily for larger pump applications. primarily for larger pump applications.

They are typically the type of pumps used on They are typically the type of pumps used on municipal water system wells. municipal water system wells.

The turbine pump is mounted The turbine pump is mounted in a large concrete vault with in a large concrete vault with a pipe connecting it to the a pipe connecting it to the lake. lake.

The water flows by gravity The water flows by gravity into the vault where it enters into the vault where it enters the pump. the pump.

The pump motors are The pump motors are suspended over the vault on suspended over the vault on a frame. a frame.

A jet pump is similar to a A jet pump is similar to a turbine pump but it works by turbine pump but it works by redirecting water back down redirecting water back down to the intake to help lift the to the intake to help lift the water. water.

Booster pumpBooster pump Most pumps are used to take water from a standing Most pumps are used to take water from a standing

(or non-pressurized) source and move it to another (or non-pressurized) source and move it to another location. location.

A booster pump is used to increase the water A booster pump is used to increase the water pressure of water that is already on its way pressure of water that is already on its way somewhere. somewhere.

Example: If you have a sprinkler system that needs Example: If you have a sprinkler system that needs 80 PSI of pressure to operate, but the water line 80 PSI of pressure to operate, but the water line coming onto your property only has 50 PSI of coming onto your property only has 50 PSI of pressure. pressure.

In this case you would install a booster pump to raise In this case you would install a booster pump to raise the pressure from 50 PSI up to 80 PSI for your the pressure from 50 PSI up to 80 PSI for your sprinkler system. sprinkler system.

Pressure vs. FlowPressure vs. Flow

The performance of a pump varies depending on how The performance of a pump varies depending on how much water the pump is moving and the pressure it is much water the pump is moving and the pressure it is creating. creating.

An important relationship not only because it determines An important relationship not only because it determines whether the pump is suitable for your irrigation system, whether the pump is suitable for your irrigation system, but also because it is these pump characteristics which but also because it is these pump characteristics which allow you to control the operation of your pump. allow you to control the operation of your pump.

The primary relationship to understand is that The primary relationship to understand is that as the as the flow INCREASES, the pressure DECREASESflow INCREASES, the pressure DECREASES

Standard formulas used to Standard formulas used to estimate flow, pressure, and estimate flow, pressure, and

horsepowerhorsepower FT.HD. = HP x 2178 / GPMFT.HD. = HP x 2178 / GPM GPM = HP x 2178 / FT.HD.GPM = HP x 2178 / FT.HD. HP = GPM x FT.HD. / 2178HP = GPM x FT.HD. / 2178

HP is brake horsepowerHP is brake horsepower GPM is gallons per minute of flowGPM is gallons per minute of flow FT.HD. is pressure in feet of head (PSI x 2.31 = FT.HD. is pressure in feet of head (PSI x 2.31 =

FT.HD.)FT.HD.) Note: these formulas have been simplified to assume a Note: these formulas have been simplified to assume a

pump efficiency of 55% which is a good average figure pump efficiency of 55% which is a good average figure to work with if you don't know the exact efficiency of your to work with if you don't know the exact efficiency of your pump. Pressure for pumps is always measured in feet of pump. Pressure for pumps is always measured in feet of head, one foot of head is equal to 0.433 pounds per head, one foot of head is equal to 0.433 pounds per square inch.square inch.

Selecting a PumpSelecting a Pump

Here's the basic procedure to follow if you're selecting a Here's the basic procedure to follow if you're selecting a pump for a new irrigation system. This is presented here pump for a new irrigation system. This is presented here as an overview to help you see where we are going with as an overview to help you see where we are going with all of this:all of this:

1.1. Estimate your flow (GPM) and pressure (feet of Estimate your flow (GPM) and pressure (feet of head) requirements and select a preliminary pump head) requirements and select a preliminary pump model to use. model to use.

2.2. Using your preliminary pump information, create a Using your preliminary pump information, create a first draft irrigation design. first draft irrigation design.

3.3. Once you have a first draft of your irrigation you may Once you have a first draft of your irrigation you may be able to fine tune your pump selection based on be able to fine tune your pump selection based on that design. Return to the pump selection process that design. Return to the pump selection process and re-evaluate your pump selection. Make your and re-evaluate your pump selection. Make your final pump selection. final pump selection.

4.4. Return once again to your irrigation design. Can it be Return once again to your irrigation design. Can it be fine tuned to better match your final pump selection? fine tuned to better match your final pump selection? Make any necessary adjustments. Make any necessary adjustments.

Pump PressurePump Pressure

First you will need to find out the "Dynamic Water First you will need to find out the "Dynamic Water Depth" of the water in your well.Depth" of the water in your well.

Dynamic Water Depth is the depth of the water below Dynamic Water Depth is the depth of the water below the top of the well, in feet, when the pump is running.the top of the well, in feet, when the pump is running.

Note that the term "draw-down" is often erroneously Note that the term "draw-down" is often erroneously used in place of Dynamic Water Depth. used in place of Dynamic Water Depth. When the pump is running, the water level in the well When the pump is running, the water level in the well

drops below the water table. It may drop a few inches drops below the water table. It may drop a few inches or more than 100 feet depending on the type of soil or more than 100 feet depending on the type of soil (or rock) the well is drilled into. (or rock) the well is drilled into.

Elevation DifferenceElevation Difference

Figure out the elevation difference between the top of Figure out the elevation difference between the top of your well and the highest point in the area to be irrigatedyour well and the highest point in the area to be irrigated

This may be a negative number if the well is higher than This may be a negative number if the well is higher than the irrigated area.the irrigated area.

Irrigation System Operating PressureIrrigation System Operating Pressure

This pressure will be calculated as part of the irrigation This pressure will be calculated as part of the irrigation design process and if you have a design already it design process and if you have a design already it should be noted on the irrigation design. should be noted on the irrigation design.

If you have an existing irrigation system that you want to If you have an existing irrigation system that you want to add a new pump to, then you can try measuring the add a new pump to, then you can try measuring the water pressure with a gauge at the point where you plan water pressure with a gauge at the point where you plan to tap the new pump into the system. This is one of to tap the new pump into the system. This is one of those unusual cases where you want to measure the those unusual cases where you want to measure the dynamic pressure, not the static pressure. dynamic pressure, not the static pressure.

So when you measure the pressure make sure that one So when you measure the pressure make sure that one of the irrigation system valves turned on and the of the irrigation system valves turned on and the sprinklers are runningsprinklers are running

Chances are you don't have an irrigation system yet, or Chances are you don't have an irrigation system yet, or even a design. In this case you will need to make an even a design. In this case you will need to make an "educated guess". "educated guess".

Minimum Pressures for Irrigation SystemsMinimum Pressures for Irrigation Systems

Drip Irrigation =70 feet head (30 PSI) Drip Irrigation =70 feet head (30 PSI)

Spray Type Sprinkler Heads =93 feet head (40 PSI) Spray Type Sprinkler Heads =93 feet head (40 PSI)

Rotor Type Sprinkler Heads =104 feet head (45 PSI) Rotor Type Sprinkler Heads =104 feet head (45 PSI)

To finish up your pressure requirement calculations you To finish up your pressure requirement calculations you add the values of the add the values of the Dynamic Water DepthDynamic Water Depth, , elevation elevation headhead, and , and operating pressure headoperating pressure head together to get the together to get the total head requiredtotal head required. .

Example:Example: You measure a Dynamic Water Depth of 25 feet in You measure a Dynamic Water Depth of 25 feet in

your well. your well. The irrigation system is 10 feet higher than the top of The irrigation system is 10 feet higher than the top of

the well. Your going to use rotor type sprinkler heads the well. Your going to use rotor type sprinkler heads so you select an operating pressure of 104 feet head. so you select an operating pressure of 104 feet head.

Your total head required would be 25 + 10 + 104 = Your total head required would be 25 + 10 + 104 = 139 feet of head!139 feet of head!

Selecting a PumpSelecting a Pump

Pump CurvesPump Curves Graph which shows the performance characteristics Graph which shows the performance characteristics

of a particular pump. of a particular pump. Pump curves are created by the pump manufacturer Pump curves are created by the pump manufacturer

and the manufacturer should be able to provide you and the manufacturer should be able to provide you with performance curves for the pumps you are with performance curves for the pumps you are considering. considering.

Remember, there is always an inverse relationship Remember, there is always an inverse relationship between pressure and flow. Higher pressures mean between pressure and flow. Higher pressures mean lower flows. Lower pressures result in higher flows. lower flows. Lower pressures result in higher flows.

Pump ControlsPump Controls

Most pump control circuits are designed using a relay Most pump control circuits are designed using a relay circuit that isolates the user from the pump voltage. circuit that isolates the user from the pump voltage.

Most relays use 12 or 24 volts, a few use 120 volts. Most relays use 12 or 24 volts, a few use 120 volts.

Automating the Control CircuitAutomating the Control Circuit

Common types include:Common types include: TimerTimer Pressure SwitchPressure Switch

Most well pumps are controlled this wayMost well pumps are controlled this way A typical installation will have a pressure tank which A typical installation will have a pressure tank which

stores pressurized water so that the pump doesn't stores pressurized water so that the pump doesn't cycle on and off rapidly due to pressure changes. cycle on and off rapidly due to pressure changes.

The tank acts as a reservoir to stabilize the pressure The tank acts as a reservoir to stabilize the pressure in the system. in the system.

Irrigation ControllerIrrigation Controller Most irrigation controllers have a pump start circuit Most irrigation controllers have a pump start circuit

built into them. built into them. You simply connect the wires that go to the switch to You simply connect the wires that go to the switch to

the controller pump start terminals, and the irrigation the controller pump start terminals, and the irrigation controller will turn the pump on whenever it turns on a controller will turn the pump on whenever it turns on a valve. valve.

Do not hook up the controller to an existing relay Do not hook up the controller to an existing relay circuit. circuit.

Flow SwitchFlow Switch Sometimes used on booster pumps. Sometimes used on booster pumps. When the switch detects flow in the pipes it turns on When the switch detects flow in the pipes it turns on

the pump. the pump. Combination of one or more of the above switches.Combination of one or more of the above switches.

A very common application is one relay controlled by A very common application is one relay controlled by both a pressure switch and a manual override switch, both a pressure switch and a manual override switch, and a second relay operated by the irrigation and a second relay operated by the irrigation controller. controller.