Page 310 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch08_265-296.qxd 8/2/10 9:53 PM Page 270

270 Chapter 8 Pumping, Storage, and Dual Water Systems

where Q water flow, gpm; H head or lift, ft; and HP power in U.S. customary unit, hp.
In the SI or metric system:
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3
MP (Q, m /s)(1,000 kg/m )(H, m)(kW/101.97 m-kg/s)
MP 9.8066 (Q)(H) (8.7a)
3
where Q water flow, m /s; H head or lift, m; and MP power in metric unit, kW. Here
1 kW 101.97 m-kg/s 1,000 watt; 1 watt 0.102 m-kg/s 1 J/s; and 1 hp 0.746 kW
550 ft-lb/s.
The total power input can be determined using the following equation:
INHP input power in U.S. customary unit (V)(A)>746 (8.8)
INMP input power in metric unit 0.001 (V)(A) (8.8a)
where V volt; and A current, amp.
The wire-to-water efficiency is the efficiency of the total power input to produce water
horsepower:
E ww (E pump )(E motor )(E ) (8.9)
o
E ww water horsepower>input horsepower (8.10)
where
E ww wire-to-water efficiency
E pump efficiency of the pump
E motor efficiency of the motor driving the pump
E o efficiency of any other parts in the entire motor-pump-wiring system.

EXAMPLE 8.2 DETERMINATION OF PUMP POWER
Determine the water horsepower, break horsepower, and motor horsepower for a pump operating
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under the following conditions: Water flow of 620 gpm (0.039 m /s 39 L/s) is to be pumped
against a total head of 135 ft (41.15 m); the pump efficiency is 80%; and the motor driving the
pump has an efficiency of 90%.
Solution 1 (U.S. Customary System):
WHP water horsepower in U.S. customary unit (Q)(H)>3,957 (8.11) (8.7)
(620)(135)>3,957 21.2 hp
BHP break horsepower in U.S. customary unit WHP>E pump (8.12)
21.2>0.80 26.5 hp
MHP motor horsepower in U.S. customary unit BHP>E motor (8.13)
26.5>0.90 29.4 hp
where Q water flow, gpm; H head or lift; ft;
Solution 2 (SI System):
WMP water power in metric unit 9.8066 (Q)(H) (8.14) (8.7a)
9.8066 (0.0391)(41.15) 15.7866 kW
BMP break power in metric unit WMP>E pump (8.15)
15.7866>0.80 19.733 kW
MMP motor power in metric unit BMP>E motor (8.16)
19.733>0.90 21.92 kW
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where Q water flow, m /s; H head or lift; m;