If you’re assessing how to upgrade your operations or installing a new pumping system, there are a variety of factors to consider, including the technologies available and the overall irrigation needs of the agricultural enterprise.
If you’re replacing an existing system, it may seem easiest to swap out the old with a comparable new version of the same system. Remember that continuous technological advancements can provide better and more cost-effective options. Plus, farms and their water sources can change over time. The current conditions of a well may mean less water at a smaller diameter borehole.
Here’s how two of today’s most popular agricultural pumping system options compare, and how they’re designed to address specific needs of the agricultural industry.
Option 1: Optimized submersible pumping systems
A complete irrigation water supply system consists of pumps, motors and controls. A submersible pumping system consists of a multistage centrifugal pump coupled to a submersible motor that has been designed for installation in a narrow well/borehole. Submersible motors are available in various construction designs, horsepower range and physical size. Submersibles are normally classified to indicate the smallest well casing diameter that will accommodate the pump: typically, from 4-inch to 12-inch. These often include power ratings as low as 1/3 horsepower up to 250 horsepower.
They can also utilize permanent magnet motors, which are growing in popularity in submersible applications. Unlike an induction motor where the internal rotor is an electromagnet and becomes energized by the system’s power supply, permanent magnet rotors are always magnetized due to the raw material selection. These internal magnetic rotors make them more efficient, especially at reduced speeds and partial loads.
Optimizing a submersible pumping system with a variable frequency drive offers several benefits in agricultural settings, such as constant pressure, soft-start protection, input and output adjustments and reporting capabilities. VFDs can account for low water levels in your well and are customizable for underload sensitivity and off time. This helps to protect your pump from dry run while it also reduces the risk of the well running dry entirely.
Option 2: Vertical lineshaft turbines
For a lot of farmers, vertical lineshaft turbines are a familiar solution for moving water in agriculture settings across the country. Besides permanent magnet submersible, they’re one of the most effective and efficient pumping system choices in high-capacity applications. Applications with high-volume pumping needs will benefit from the efficiency and smooth operation VLSTs offer.
Another consideration for VLSTs is their ability to move water exposed to sandy soil when configured with a semi-open impeller. This impeller design allows the flow of sandy water while lessening the wear and tear of the pump. In these semi-open impeller situations, it’s also important that the well and pump be installed and adjusted properly. Otherwise, efficiency may suffer. As the impeller wears, it can be readjusted periodically to perform optimally. This involves some added scheduled maintenance but allows maximum usage of the pump life.
A major drawback for these systems is durability and longevity. For a VLST, there are many extra parts that can wear and need to be maintained or replaced. The VLST also has an above-ground footprint that needs to be accounted for whereas a submersible system has a much smaller footprint.
Weighing the benefits of each option
If you’re weighing the merits of installing a submersible turbine pump or a VLST, you’re probably wondering how to choose. Ask yourself these questions:
- How high of a flow rate do you require? Submersible lines often feature bowl sizes up to 12 inches while lineshaft pumps go up to 42 inches, making them better for very high-capacity applications.
- What role does price play in your decision? With both types of pumps, pricing can depend on a lot of variables: How deep are you setting the system? What horsepower do you require? In terms of installation, smaller horsepower motors are typically less expensive to set in a submersible application.
- How impactful is the cost of maintenance downtime to your operations? Submersible pumps feature fewer moving parts, which can mean easier initial installation and less scheduled maintenance down the road. Keep in mind, due to pre-lubrication requirements for lineshaft and bearings, VLSTs demand a more involved initial installation process than submersible pumps.
- Do you need the capability to replace your motor down the road? Motors in VLST installations are typically more accessible and therefore easier to replace.
- Are you looking for quiet operation? If your well is close to office space, residential areas or even sensitive livestock, you want to keep noise at a minimum. In these applications, a submersible pump is the better choice since it operates at a lower decibel level.
When it comes to application-specific considerations, take into account the following aspects of your installation:
- Is your well straight or misaligned? If you’re installing a pump and you happen to come across a misaligned well, a submersible pump is typically the better choice. A lineshaft and its bearings require a specific alignment, which can be challenging to achieve in a crooked well.
- Do you need high flow from a reduced diameter borehole? Submersibles are typically operated at higher speeds than lineshafts, enabling them to move more water with a slimmer diameter pump.
- Do you have a top feeding well or open water application? If you are solving pumping needs for these applications, consider a VLST that will not demand any cooling flow requirements due to its design, while a submersible turbine may require a flow sleeve to ensure adequate cooling flow past the motor.
- What power source is available and how reliable is it? Do you need a diesel-driven backup option? Some ag pumping situations can withstand a short period of downtime, while others cannot. If you’re concerned about the reliability of your electric source, you may need to install a pumping system that includes a diesel-driven backup. Vertical lineshaft pumps featuring a gear drive can deliver this flexibility.
- How clear is the water you’re moving? For areas with sandy soil, such as Texas and the Mississippi Delta region, a semi-open impeller design in your pump can help lessen its wear and tear.
When it comes to comparing and selecting the best pump for an agricultural application, online tools can provide guidance and allow selections to be made across multiple product categories for a single application. These tools will factor in unique needs to narrow down the hundreds of different pump configurations available into the one that will maximize investment and deliver reliable water management for your farm for years to come.
As featured in Irrigation Today's article: Weigh Your Options When Replacing a Pumping System
Brandon Schumm is a senior product manager for Franklin Electric. He has earned vast experience throughout his previous roles in manufacturing/application engineering, sales, marketing and product development. He can be reached via email.