Page 251 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

t
Tolerance
Impeller Wear Ring

factory setting. This setting is based on the operating temperature of
the application. Let’s consider how much money the lost efficiency
costs. We will use some formulas from Chapter 5 in this book on useful
work and efficiency.

0.000189 x GPM x TDH x $Kwh x sp.gr. x 8,760
Cost per year =
Eff. Pump x Eff. Motor
where: 0.000189 = Conversion factor
GPM = Gallons per Minute
TDH = Total Dynamic Head
$Kwh = Cost per Kilowatt-hour
sp.gr. = Specific Gravity
8,760 = Hours in a year
Eff. Pump = Pump Efficiency
Eff. Motor = Motor Efficiency
To show cost increase, consider this newly installed pump in a properly
designed system. We have the following values:
GPM = 2,000gpm
TDH = 120ft.
$Kwh = $0.10
sp.gr. = 1 (water)
Eff. Pump = 77%
Eff. Motor = 93%
The electricity cost to run this pump for a year is $55,450.80.

Mer being in line for six months, this pump is disassembled and it is
noted that the tolerance in the wear bands has opened 0.004 inch from

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