Page 284 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

However, as the discharge of water takes place in this type of pump only during the discharge stroke, the pump
creates a pulsating flow of water and not a continuous flow. This type of pump is called a piston pump.

Rotary pumps : There are very many varieties of this pump in the market. However centrifugal pumps, jet pumps
and submersible pumps are the commonly used pumps for lifting water in houses.
Centrifugal pumps : Fig 2 shows the construction and operation of a centrifugal pump.
The operation of a centrifugal pump is based on centrifugal force. As the fluid being pumped enters the inlet or
central section of the pump, the rotating action of the impeller vanes forces it to the outside of the pump casing
(Fig 2).
Fig 2

Because the fluid moves faster at the outer edge of the impeller the momentum increases. As more fluid enters
the pump, more fluid momentum is built up in the casing that encloses the impeller. This momentum forces the
fluid out of the pump discharge port.
The centrifugal pumps are used where large volumes of water are to be pumped at relatively low pressure.
Submersible pumps : This pump also comes under the category of centrifugal pumps and is found in use at
places where water is found in great depth.
Submersible pumps have motor and pump in an axial length are submerged in water (Fig 3). Generally such
pumps are used for borewells where the volume of water to be lifted exceeds the capacity of reciprocating pumps.
The motor used in such types of pumps is of 3-phase.

Fig 3

The cables and motor windings have water proof sealing as they are immersed in water. Such pump sets will have
following advantages.
– Diameter is smaller.
– Motor and pump are submerged in water. Hence needs no space on ground level.
– The motor and pump are entirely connected through metal pipes for delivering water.
– Efficiency is more as the motor with the pump will be to the level of water or inside the water.

271
CITS : Power - Electrician & Wireman - Lesson 101-103