Optimizing Pumping Systems for Agricultural Irrigation: Selecting the Best Solution for the Application
Reliability is critical with any pumping system, but in agricultural settings reliable water management can mean the difference between either a profitable or catastrophic growing season where a downed or declining system can result in a lost crop cycle, but consistent and precise coverage equates to better yields. So how do pumping professionals recommend and install the best pumping solution for the application? Can they recommend systems that maximize available resources and align maintenance within each grower's preferred range?
Optimizing agriculture irrigation starts with evaluating each potential site layout and the grower's needs. Does the system need to pull water from a lake or pond? Or will the system be set in a well? Will the pumping be performed on a schedule? These variables can heavily influence the type of system that is ideal for each project – whether it’s a lineshaft turbine, a submersible turbine, or a centrifugal pump. Understanding the performance parameters of each type of pump can help installers select the best solution for the application – and help deliver timely servicing during peak seasons.
From Shallow to Deep Well Settings: Address Water Supply with Submersible Pumping Systems
Submersible pumps are rugged, electric-driven systems designed to draw water from wells as shallow as 10 feet or as deep as 3,000+ feet. With submersible pumping systems, both the motor and pump are installed within a well and underground, protecting them from weather, implements, livestock, and other surface hazards.
Submersible pumping systems are available in most common voltages and frequencies for U.S. and international locations, making them versatile when electricity is readily available and reliable. When evaluating a submersible pumping system, it’s important to consider several key components – including flow and head requirements, set depth, casing size, screen location, and controls. Installers can also leverage the latest technology, permanent magnet motors, to deliver higher efficiency, which equates to cost savings on operation.
Even if power isn’t readily available, some farming operations can still utilize solar-based pumping systems. These convert alternative energy sources to a DC power supply. The DC power goes through an inverter with max power point tracking to supply AC current to a standard AC motor and pump. There are some size parameters to these systems, so installers will need to work with a manufacturer that understands the benefits and limitations of solar power.
Tackle High-flow Demand: Vertical Lineshaft Turbines
Vertical lineshaft turbine systems utilize a submerged pump, a shaft system installed from pump to surface, and a driver that is located above ground. Vertical lineshaft turbines can be installed anywhere from 10 feet to 2,500+ feet below grade and move up to 42,000 gallons per minute. Applications include supply to pressurized irrigation systems, filling settling reservoirs, boosting pressure from a wet well, flood irrigation, extensive water features, and much more. A vertical lineshaft turbine delivers several key benefits, including:
Serviceability: When uptime is critical, vertical lineshaft turbines allow for flexible servicing on both new and existing systems. A pump or bowl assembly can be replaced while the column, tube, shaft, discharge head, and motor are retained. When sand and other debris consistently wear components, semi-open impellers can be reset to optimize flow.
Durability: The materials used throughout the key components of a pumping system can prolong its lifecycle. For example, systems that utilize silicon carbide mechanical seals can pump water that contains silt, sand, or other mildly abrasive particles that are found in agricultural settings. These types of seals also help users avoid reliance on full oil cans for adequate shaft lubrication and dripping at the discharge head.
Move Massive Volumes of Water: Mixed or Axial Flow Lineshaft Turbines
Mixed flow and axial flow vertical turbine pumps are both good choices when the application demands a high flow. Axial flow pumps allow for shallow depth sets up to 35 feet while mixed flow work in depths up to 150 feet. Both are ideal for applications where you need to move a lot of water that is readily available – for example, from a lake or pond.
Move Large Volumes of Water at the Surface: Centrifugal Pumping Systems
A centrifugal pumping system is used in surface water applications, providing a versatile solution to a variety of agricultural irrigation needs. Common applications include boosting water pressure from creeks, rivers, reservoirs, and canals, water transfer across fields, and center pivot end gun boosters.
Sometimes referred to as above-ground or surface pumps, these systems can be packaged with a variety of industry standard motors and must be primed when the water level is below the pump suction.
Centrifugal pumps are relatively easy to maintain and have few moving parts, reducing the likelihood of breakdowns. They are also generally inexpensive systems compared to other types of pumps, and they can handle both clean water and suspended abrasives common to rivers, canals, and reservoirs.
Prolonging the System’s Life & Improving Efficiencies: Don’t Forget the Drive
Any agricultural pumping system is an investment for the grower, including operational expenses. That’s where controllers come in. They not only optimize performance but also provide varying levels of system protection from the power supply and operating conditions.
A variable frequency drive (VFD) is an example of a controller that offers built-in features designed to protect and extend the life of the pumping system. VFDs help with control, data gathering, troubleshooting, and efficiency, providing precise water delivery to the fields. For example, dry seasons lead to lower water levels; VFDs offer programmable low water level settings to dial in the trip points, ensuring the system shuts down when the pump starts pulling in air with the water. This protection feature also allows programmable recovery time, giving water levels time to recover and reducing the harmful effects of surging the well.
VFDs can also optimize an irrigation system to deliver constant pressure with varying flow requirements and water levels. Whether supplying water to a center pivot, multiple sprinklers, a drip system, or misters, the system can be designed to perform efficiently across the board. Constant pressure systems deliver the right amount of water across a property without gaps to maintain consistent yield. Constant pressure allows operators to dial in the ideal pressure required to operate their nozzles and emitters to what is best for their application and crops.
VFDs can be as complex or simple as needed for the user and application. Drive solutions can be fabricated with several options including status lights, service-entrance rated disconnects, input and output filtering, and communications or telemetry. When rated for outdoor use, they save time in building a structure to house them. You can program multiple speed set points with well level measurement devices to avoid running the well dry. Optional telemetry controls allow the grower to control the system remotely and compile data using a smartphone or computer.
An alternative to advanced control with VFDs is a reduced voltage soft starter. These controls limit the voltage and torque while the motor is starting to facilitate smooth current progression; this process reduces electrical costs from startup current, power supply stress, mechanical wear, and hydraulic shock. Soft starters accept dry and voltage input signals, do not require complex electrical filtering, and often utilize a bypass contactor for system reliability. Whenever controlling the startup time of a motor, ensure the time does not exceed the manufacturer's recommended length.
Use Case Examples: Center Pivot, Liner or Subsurface Drip Irrigation Systems
The location and long-term irrigation strategy can dictate the type of irrigation system needed. Rotating crops, tilling practices, and limited growing seasons can shift an irrigation system toward center pivot or linear methods. These systems can be simple single operation point designs or complex with corner systems/variable rate nozzles that require VFDs for consistent operation. High value vegetables, smaller or abnormal shaped grow areas, or limited water availability requiring maximum irrigation efficiency may encourage the use of drip irrigation. These systems can require advanced controls for even application and filtration methods to eliminate abrasives clogging small nozzles. Multiple pumping systems can be used depending on the complexity and operator preferences.
In each case, the pumping system you select is highly specific to the requirements of each project. Lineshaft vertical turbines can experience long life cycles but require consistent lubrication, motor maintenance, and environmental protection at times. Submersible pumps and motors generally offer low maintenance and long life with initial investment ensuring knowing screen location, control parameters, and potential for suspended abrasives. Centrifugal pumps offer moderate cost, easy maintenance, and mobility with surface water.
Conclusion
Optimizing water delivery in agricultural settings is a challenge. A firm understanding of the most common pumping systems – and how the technologies work – assures consistent and reliable irrigation across the variety of projects you are bound to encounter.
As featured in the Water Well Journal article: Optimizing Pumping Systems