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Product Documents


Additional information


Coupling Type


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Input power range kw

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Maximum input power (kw)


Transfluid has designed their KSL series variable fill fluid coupling to overcome problems experienced at “start up� and “speed variation� operation for medium and high power machines driven by electric motors and internal combustion engines.


Extremely efficient perfomance is achieved operating the KSL’s very simple and effective principle. Oil that’s the power medium is pumped from a sump to the hydrodinamic coupling circuit where it is finally “drained off� through a series of orifice plugs back into the sump.

The “START UP� principle:
By controlling the coupling’s feed pump oil flow to the working circuit by a small A.C. frequency converter changes occur inside the coupling working circuit which alter the coupling slip characteristics and this softens the “start up� dramatically.

The “VARIABLE SPEED� principle:
The same principle used to control the start-up permits the KSL to operate as variable speed drive varying the speed between input and output.

Its “TORQUE LIMITING� function:
Another KSL feature is its ability to limit the torque transmitted slipping for a time and then dumping its circuit oil disconnecting the driven machinery. The quick disconnection is possible by installation of quick realease valve.

The key “KSL� features are:

  • soft start
  • variable speed
  • torque limiting


Soft starter
The KSL’s fluid coupling working circuit is gradually filled with oil from an empty condition to a fully filled condition. Such behaviour enhances an extremely soft controlled start up especially with high inertia machinery. The KSL’s variable oil feed system is controlled by a frequency converter during the ramp up producing the ideal soft starter.

Accurate speed variation
By operating either manually or by the frequency converter controller the KSL always guarantees output speed accuracy as required by operator or control system.

Vibration Dampening
One of the most important characteristics of KSL fluid coupling is its torsional vibration dampening effect protecting both the driven machine as well as the motor or engine.

Overload Protection
This is a fluid coupling peculiarity and a big benefit to users. Even more protection can be achieved by installing “quick release drainable valves� which discharge oil from the working circuit in a few seconds limiting any prolonged overload period completely.

High Efficency
The KSL is an extremely efficient device compared to the constant filled type fluid coupling as its volume of working ciruit is controlled at the fullest possible volume to mantain a very small slip rate.

Shaft Labyrinth Sealing
These make the KSL series a low maintenance piece of equipment.

Ease of Maintenance
Thanks to its split casing design it’s possible to remove the complete fluid coupling impeller assembly without having to move either the motor/engine or driven machinery saving the need for realignment and costly down time. In addition all the accessories are externally mounted allowing an easy and fast replacement in case of need.


To correctly select the right coupling Transfluid needs to know the following:

  • Motor/Engine type power and speed
  • Driven machinery type power and speed
  • Output speed range
  • Environmental conditions
  • Cooling water characteristics
  • Assembly configuration
  • Drive and driven shaft dimensions and tolerances.

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