An irrigation pump is a mechanical device used to move water from a source to a distribution system for agricultural or landscaping purposes. They ensure crops and plants receive water, especially in regions with unreliable rainfall. Pumps convert energy from an external source, typically an electric motor or combustion engine, into hydraulic energy that moves the water.
The pump draws water from a source, such as a well, river, lake, or reservoir, and delivers it through pipes to the field. By creating pressure and flow, the pump allows water to reach every part of the land, overcoming both distance and elevation changes.
How Irrigation Pumps Move Water
Irrigation pumps convert mechanical energy into hydraulic energy (flow and pressure). This process involves the actions of suction and discharge to create continuous water movement. Suction lift is the initial step, where the pump creates a low-pressure zone at its inlet, drawing water from the source into the pump casing.
Once inside the pump, the mechanical component, often an impeller, increases the water’s velocity and pressure. The water is then forced out through the discharge port under pressure. For pumps operating above the water source, the vertical distance water is pulled up is the suction lift, which is physically limited to about 33 feet at sea level.
The pump must create enough discharge pressure to overcome the system’s total resistance, including vertical height and friction losses in the piping. This action transforms the water’s kinetic energy (velocity) into potential energy (pressure) as it leaves the pump and enters the distribution network. The efficiency of this energy conversion determines how much power moves the water.
Major Categories of Irrigation Pumps
Irrigation pumps fall into two main categories based on their operating principle: dynamic pumps and positive displacement pumps. Dynamic pumps, most commonly centrifugal pumps, use a rotating impeller to continuously increase the speed of the water. The water is accelerated by the impeller and then directed into a progressively widening casing, which converts the high velocity into high pressure.
Centrifugal pumps are the most popular choice for irrigation due to their ability to handle high flow rates and variable pressures. End-suction pumps are often used for small to medium applications, mounted above the water source. Vertical turbine pumps and submersible pumps are specialized centrifugal designs used for deep wells; submersible models have the motor and pump encased underwater, eliminating the need for priming.
Positive displacement pumps operate by trapping a fixed volume of water and forcing it into the discharge pipe. Unlike centrifugal pumps, their flow rate is constant regardless of the pressure they are pushing against. Though less common for large-scale crop irrigation, pumps like piston or diaphragm pumps are used in applications requiring very high pressure or precise, low flow rates.
Determining the Right Pump for Your Needs
Selecting the correct irrigation pump requires assessing the system’s hydraulic demands, involving two primary metrics: flow rate and Total Dynamic Head (TDH). Flow rate is the volume of water the system requires, typically measured in gallons per minute (GPM) or liters per minute. This figure is determined by the crop water needs and the size of the area to be irrigated.
Total Dynamic Head (TDH) measures the total resistance the pump must overcome to move the required flow. TDH is the sum of three components: static head (the vertical distance the water must be lifted), friction head loss (pressure lost due to friction in pipes and fittings), and pressure head (operational pressure required at the system’s end). Calculating TDH accurately ensures the pump has the power to reach the farthest or highest point of the system.
The power source influences operational flexibility and cost. Electric pumps are common for smaller, permanent installations due to their low maintenance and consistent power. Diesel or gasoline engine-driven pumps offer portability and high power for remote or large-scale applications. Matching the system’s required flow rate and TDH to the manufacturer’s published pump performance curve is necessary for selecting an energy-efficient pump.