3 August 1998
100 + 20 = 120 ft.
b. Discharge head is the difference in elevation from the pump to the water level in the
storage tank. Calculate the difference in ground elevation and add the required pressure.
Assume the well is at El. 695.
(820 - 695) + (40) (2.31)
= 217 ft.
c. Friction head is calculated by methods presented in TM 5-813-5. Add head loss in pipe
plus loss in fittings.
(18 ft/1000) (1.5) + 10
= 37 ft.
d. Velocity loss is calculated from the equation.
= 0.25 ft.
e. Total dynamic head is the sum of the above.
120 + 217 + 37 + 0.25
= 374 ft.
Calculate the pump horsepower using equation 5-7. Efficiency can be found in manufacturer's
= 41.2 hp.
B-7. SPECIFICATION PREPARATION. Given the above information, the designer can review
manufacturer's literature and consult with their representatives to determine types of pumps
and motor drives which are available to meet the operating conditions. The calculations can
then be refined to account for actual pump and well characteristics. Although not a function of
well design, the engineer may want to oversize the transmission main from the well to the
storage tank to allow for future expansion or make other modifications in the design. The
calculations should be reviewed when all systems are finally sized. The well diameter may be
oversized to allow for future installation of a larger pump, but the pump installed should not
exceed the capacity of the well. This procedure gives sufficient information to specify a water