3.2.4 Irrigation pumps
Irrigation pumps
Irrigation pumps are used within agriculture to pump a controlled amount of water to plants at regular intervals with the objective to increase crop yields. Irrigation uses groundwater, surface water, and water delivered directly from public water supply but since water cost is a critical profitability factor for farmers and companies involved in industrial cultivation most of the water is from a self sufficient source. To distribute water through hoses with holes (drip irrigation), piping systems to ponds, tanks and sprinkler nozzles makes use of many different pumps depending on the construction of the irrigation system and driving sources available.
Common types of pumps involved for irrigation systems:
- Deep well, submersible pumps
- Deep well pumps with ejector (Jet pumps)
- Turbine pumps
- Centrifugalpumps (end suction)
- Centrifugalpumps (self priming)
- Booster pumps
- Metering pumps
The function and design of the pumps above are all described in detail at pages for each pump respectively.
What pump to use depend on how to get the water (groundwater, surface water) and how to power them. How much water they need to distribute, how high the pumps need to lift and how extensive the system is will determine the size of the pump. Permanent installations normally have single stage pumps in accordance with standard water pumps or multi stage pumps. When wells have been bored, submersible deep well pumps are used. The driving source is generally an electric motor although anomalies in the electric tariff system can also make diesel operation a favorable alternative, even by using second hand truck engines. The required water flow depends on the type of spreader and the area to be irrigated and normally lies within the range 10-100 m³/h. The pump delivery heads are relatively high in the order of 50-120 m. Metering pumps are used for creating very precise flow volumes, or creating very high pressures, they are also used in irrigation for fertilizer injectors (mixing fertilizer into irrigation water) or sometimes as spray pumps.
Cost of water has been mentioned as one important factor, for self sufficient water supply farmers must consider energy consumption. Energy for irrigation pumps is one of the highest single cost drivers. In recent years a prominent part of agriculture have started to use technological innovation to increase efficiency and effectiveness of their irrigation system. This can be done in many different ways depending on need and what is possible to achieve but the key to efficient pumping is efficient control of volume flow. Control of volume flow from source to plant reduce risk of leakage (efficient use of produced water).
Since irrigation demand is ever changing due to rain and temperature as well as level in ponds or access to water, irrigation pumps tend to be sized for the worst case scenario which mens they tend to be over sized. Speed control is a very efficient way to reduce capacity on over sized pumps. Reducing the speed and thereby the flow is also reducing the power drawn from the motor and thus, the electrical cost. Control of pump speed using frequency inverter will optimize pumped volume to actual need and reduce (cost) power consumption per volume (kW/m³).
