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COOLING SYSTEM
Typical fan performance graphs have total pressure curves and power absorption curves for a
given speed of rotation. The pressure, measured in water gage, represents the resistance to
fl
ow.
The higher the resistance, the lower the
fl
ow. The fan horsepower absorption follows a similar,
but not exactly the same, characteristic to the pressure curve. Depending on the installed system
characteristics, the fan operates only at one point of water gage and power.
Most fans have some region in which the
fl
ow separates from the blade and the
fl
ow becomes
unstable. This is called a stall region. Operation in the stall region is not recommended because
results are not consistent and the fan is inef
fi
cient and noisy.
There are maximum tip speeds in the range of 18,000 to 23,000 feet per minute that the fan
manufacturer based on his design. Check with the fan manufacturer.
The system characteristics are de
fi
ned by the air
fl
ow restrictions that are a result of:
□
Engine enclosure louvers
□
Engine and accessories
□
Fan guard
□
Radiator core
□
Charge air cooler if in tandem with radiator
□
Oil cooler if in tandem with radiator
□
Bug screen
□
any other internal or external obstructions
NOTICE:
The fan should never operate in the stall area, where a small
change in static pressure results in no change in air
fl
ow.
NOTICE:
The air side of the cooling system is critical and a change in the
air
fl
ow will generally have a greater impact on cooling than a
similar percentage change in coolant
fl
ow.
7-30
All information subject to change without notice.
(Rev. 03/06)
7SA250 0603
Copyright © 2006 DETROIT DIESEL CORPORATION