Suction Lift Applications
In a suction lift application, the system does not have incoming pressure, but is instead pulling from a water source, such as a lake, river, sump, etc. Pumps in suction lift applications can realistically lift water 15 to 20 feet maximum, depending on the elevation. A suction lift application may pull water from a lake, river, sump, etc.
Suction lift applications commonly require the use of horizontal centrifugal pumps and vertical turbines. Vertical multistage pumps are not recommended for suction lift applications in irrigation systems due to net positive suction head required (NPSHr) constantly changing in a variable flow irrigation system.
An advantage of horizontal centrifugal pumps is that they are easier to install and maintain because the internal parts are easily accessible. In a suction lift application, the horizontal centrifugal pump moves water vertically, lifting it up from the water source to feed into the pump intake. Centrifugal pumps can also accommodate both low suction pressure and high suction pressure needs.
Vertical turbines and submersibles are suited to suction lift applications, since they are located in the water and do not need to create the vacuum to lift water to the pump intake.
A vertical turbine can be installed close to the bottom of the sump, making good use of available water. In sump or open water applications, submersibles should be installed with flow sleeves to drive the water past the motor to avoid the motor overheating, unless the submersible is a bottom suction configuration, which incorporates a flow sleeve in its design.
Variable Frequency Drives & Irrigation Systems
VFDs are not required for smaller irrigation systems with nonvarying flows. They are recommended for larger systems to enable soft starts and energy reduction.
VFDs give irrigation systems the ability to react to variations in consumption, making the system more efficient and reactive. For pumps with steep pump curves, VFDs can elicit a faster, more controlled reaction to changes in flow than in pumps with a flat pump curve. Vertical turbine pumps, submersibles and vertical multistage pumps are all available with steep curves and can benefit from VFDs.