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a device in the form of a tube (usually with a diameter of 40–70 mm) that has a filter at the end and is used to lower the level of groundwater. Two types of well points—the light and ejector types—are used.
A light well point is connected by a rubber hose and a vacuum conduit to a pumping unit located on the surface. Water is pumped out by means of rarefaction in the well point and conduit, which is produced by a vacuum pump. The height of lift of the water may be up to 6 m. In an ejector well point the water is pumped and a vacuum that promotes drying of the rock is created by an ejector (water-jet pump) mounted within the well point. The ejector is driven by a jet of water forced through the distribution duct by a centrifugal pump located on the surface. An ejector well point raises water from a depth of 18–20 m.
A concentrated ejector well point (a so-called concentric vacuum hole) that makes possible accelerated drying of all water-bearing beds has been developed and introduced in the USSR for complex hydrogeological conditions (interstratification of water-bearing and waterproof rocks, low water permeability, and the presence of quicksand).