Tube Well
http://en.wikipedia.org/wiki/Tube_well
A tube well is a type of water well in which a long 100200 mm (5 to
8 inch) wide stainless steel tube or pipe is bored into an underground
aquifer. The lower end is fitted with a strainer, and a pump at the top lifts
water for irrigation. The required depth of tube well depends on depth of water
table.
The tube well casing houses the inlet, cylinder,
piston valves and rising main of a “down-the-hole” type hand pump.
Casing to support the external surfaces of the borehole against collapse may be
needed, either temporarily or permanently, and is often made of PVC pipe which
is both cheap and inert.
Seepage down the tube well bore is prevented by
the sanitary seal. Seepage from the ground above the aquifer is excluded by the
lengths of plain casing. Water to be pumped is admitted through slots in the
lower lengths of casing.
Water abstracted from aquifers in relatively
soft ground usually contains sand or silt particles, which are liable to cause
rapid wear to pump valves and cylinders (and dissatisfaction among consumers).
Methods of preventing these particles from reaching the pump are of two general
types, screening and sand/gravel packing.