Science of Water : Concepts and Applications

332 The Science of Water: Concepts and Applications
Solution:
Before fi eld bhp can be calculated, the shaft loss must be factored in:
Now the fi eld bhp can be determined:
⎛ 029 . hp loss⎞
( 170 ft) 0.5 hp loss
⎝
⎜
100 ⎠
⎟
Field bhp bowl bhpshaft loss, hp
51.8 bhp0.5 hp
52.3 bhp
Example 10.14
Problem:
The fi eld horsepower for a deep-well turbine pump is 62 bhp. If the thrust-bearing loss is 0.5 hp and the
motor effi ciency is 88%, what is the motor input horsepower? (Use Equation 10.8.)
Solution:
field (total) bhp
mhp
motor efficiency100 62 bhp 0.5 hp
0.88
71 mhp
When speaking of the effi ciency of any machine, we are speaking primarily of a comparison
of what is put out by the machine (e.g., energy output) compared to its input (e.g., energy input).
Horsepower effi ciency, for example, is a comparison of horsepower output of the unit or system with
horsepower input to that unit or system—the unit’s effi ciency. In regard to vertical turbine pumps,
there are four types of effi ciencies to be considered:
•
•
•
•
Bowl effi ciency
Field effi ciency
Motor effi ciency
Overall effi ciency
The general equation used in calculating percent effi ciency is:
part
% 100
whole
(10.13)
Vertical turbine pump bowl effi ciency is easily determined using a pump performance curve
chart—provided by the pump manufacturer.
Field effi ciency is determined using Equation 10.14:
(field head, ft)(capacity, gpm) 3960
Field efficiency, %
100
total
bhp
(10.14)