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Table of Contents
                            Vision 2020
Document Text Contents
Page 23

times DWF and third pump of capacity 3 times DWF. For larger pumping stations
five pump
sets are provided with capacities of 2 units of 0.5 DWF, 2 pumps of 1 DWF and
one pump of
3 DWF.

Head Requirement
Head describes pressure in terms of lift. The discharge head on a pump is a sum
of the
following contributing factors:
1) Static Head (hd) - The vertical distance through which the liquid must be lifted
i.e. the
lowest water level in wet well and highest point on the discharge side.
2) Friction Head (hf) - The resistance to flow caused by friction in the pipes,
valves, and
bends. Entrance and transition losses shall also be included. The loss of head in
friction in the
pipes is estimated from the well known equation hf = fLv2/(2gD)
3) Velocity Head (hv) - The head required to impart energy into a fluid to induce
Normally this head is quite small and can be ignored unless the total head is low.
This is
estimated as v2/2g.
4) Pressure Head (hp) - The pressure differential that the pump must develop to
deliver water
on the delivery side under higher pressure. The pressure on water in sump well
is usually
atmospheric pressure, whereas when pumping into sewers there would be
potential head at
the point of delivery, against which the pump have to deliver. Thus, this is the
between pressures on the liquid in the wet well and at the point of delivery.
Total Head (H) of pumping is thus expressed by the following equation:
H = hd + hf + hv ± hp (2)

Suction Lift
The amount of suction lift that can be handled must be carefully computed. It is
limited by
the barometric pressure (which depends on elevation and temperature), the
vapor pressure
(which also depends on temperature), friction and entrance losses on the
suction side, and the
net positive suction head (NPSH) - a factor that depends on the shape of the
impeller and is
obtained from the pump manufacturer.


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