Contents preface (VII) introduction 1—37

4.12. PUMPING EQUIPMENT FOR WATER WELLS
In most wells, the static water level is below the ground surface and, hence, flowing wells are rare. The water has to be lifted from inside the well to the ground surface. Rope and bucket with or without windlass have been used and are still used for shallow wells and for low discharges. For deeper wells and high yields of water, pumps have to be used.
The purpose of installing pumps in wells is to lift water from inside the well to the ground surface. Pumps can be broadly classified as shallow well pumps and deep well pumps depending upon the position of the pump and not the depth of the well. A shallow well pump is installed on the ground and lifts water from the well by suction lift. A deep well pump is installed within the well casing and its inlet is submerged below the pumping level. If the pumping level is lower than the limit of a suction lift (about 7.5 m), only the deep well pump should be used.

GROUND WATER AND WELLS

161

Pumps are also classified on the basis of their design as positive displacement pumps and variable displacement pumps (6). Positive displacement pumps discharge almost the same volume of water irrespective of the head against which they operate. The input power, however, varies in direct proportion to the head. Such pumps are used extensively in ground water monitoring wells, hand pump-equipped wells, and wind-powered wells. They are rarely used for large-capacity water wells. The most common type of positive displacement pumps is the piston pump.

The variable displacement pumps are used for large-capacity wells. For these pumps, there is an inverse relationship between the discharge and the working head. Maximum input power is required when the pump has to operate at low heads delivering large volumes of water. The major types of variable displacement pumps are as follows (6):
(i) Centrifugal pumps: (a) suction lift pump,

(b) deep-well turbine pump, and (c) submersible turbine pump.

(ii) Jet pumps (iii) Air-lift pumps