3.2.7 Deep well pumps with ejector

Deep well pumps with ejector

Deep well pumps with ejector complement the previously described automatic water pumps when the level of the water in a well or, primarily in a borehole (deep bored in rock) lies more than 5 to 7 metres below the location of the pump. An ejector (or jet pump, see also group Jet pumps) is placed below the surface of the water in the borehole, which is supplied with motive water from a pump located at ground level (or as required). By means of the ejector, the water from the borehole together with the  motive water is transported to the pump. lt follows that it is necessary to have two hoses or pipes, see figure 3.271a, between the pump and the ejector. Discharge water is taken from a separate outlet on the pump. For multi stage pumps this outlet is located approximately in the middle of the pump.

By using an ejector the level of the water can be more than 100 metres below the pump. In as much as the water supply to a borehole is small, dry running of the pump system can be avoided if the ejector is equipped with a suction pipe which is a little more than 10.3 m long. A self regulating effect is thus created due to cavitation (the formation of vapour) in the ejector. The pump system is primed prior to initial start by filling a small reservoir (self priming device) on the pump. During normal operation, start and stop is performed automatically by the pressure difference in a hydrophore or a pressure cell equipped with a diaphragm.