Efficiency

There are two kinds of losses present in hydrokinetic, hydrodynamic, and hydroviscous couplings. First, we will consider what are termed circulation losses. They are made up of bearing friction, windage, and the power required to accelerate the oil in the rotor. On internal pump units, the power required to drive the oil pump is included. As an average, these losses represent approximately 1.5% of the unit rating, and for most purposes these losses may be considered as being constant, regardless of output speed.

Second are slip losses. As is the case on similar slip machines such as mechanical clutches and eddy-current couplings, the torque on the input shaft equals the torque on the output shaft. Therefore any reduction in the speed of the output shaft has a directly related power loss inside the machine. In other words, output speed

input speed

The total fluid drive losses are the sum of the two inefficiencies. The complete energy formula is

In USCS units

. ,, output horsepower / circulation horse-A

output speed/input speed V power losses J

In SI units output kilowatts circulation

Fluid drive input kilowatts =-—-r + I . ., .. , output speed/input speed kilowatt losses

At maximum designed operating speed (which is usually about 98% of driven speed), the total coupling efficiency is approximately 96.5%, with 1.5% of the losses being circulation losses and 2% being slip losses. The hydroviscous unit can be operated at 100% driven speed, but under these conditions it is not a fluid coupling.

Because the circulation losses become relatively insignificant at reduced speeds, approximate calculations may be made using the formula output speed

input speed

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Survival Treasure

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