SPIS Toolbox - Water Pump
Water pump
Depending on the water source, there are two different possibilities for pump installation – submersible or surface. Surface pumps are often installed next to the water source andsuckwater up on one side before “pushing” it away on the other side of the pump. Surface pumps can pump water up from a maximum depth of six meters. Submersible pumps are installed under water in wells and boreholes and “push up” thewater.
Submersible pumps are installed at depths ranging from 10 to 120 meters. Using control switches (such as float switches in water tanks and wells), submersible pumps can be operated in automatic mode. In contrast, surface mounted pumps usually require the attendance of an operator who regularly checks the surface pump’s priming behavior. Use of primary chambers and non-return valves can prevent loss of prime, but are not very reliablein practice. Therefore, surface pumps are considered to be less reliable than submersible pumps.
Solarwaterpumpsaregenerallyconstructedfrom non-corrosivestainlesssteelandaredesignedto pumpcleanwaterwithoutanysolidsandfibers. The lifetime of a submersible motor pump strongly depends on the water and installation quality. If the pump is installed in a drilled well withaproperwellcasing(andthusreducedsediment intrusion), submersible pumps may reach lifetimes between 7–10 years. In very poorly constructedwells and boreholes with high sediment content, the hydraulic part of the water pump may have to be replacedafter2–3years.Inordertosecureasafe systemoperation,twosafetymeansarenecessary:
- a water level sensor installed in the storage tank that switches off the pump in order to avoid overflow;
- a second water level sensorinstalled towards the base of thewelltoavoiddryrunningofthepump.
There are two types of pumps to be typically found in today’s solar pumping systems: centrifugal and helical rotor pumps.
Centrifugal pump
A centrifugal pump creates an increase in pressure by transferring mechanical energy from the motor to the fluid through the rotating impeller. The fluid flows through the inlet to the impeller center and out along its blades. The centrifugal force increases the fluid velocity and consequently the kinetic energy is transformed to pressure. The pressure can be increased by simply adding several stages in series. Centrifugal pumps are generally utilized where pumping heads are low and water demand is high. For this reason centrifugal pumps are the preferred option for use in irrigation systems.
