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Thread: Fluid coupling

  1. #1
    srikanth Guest

    Fluid coupling

    I have just started my profession in bulk handling, please answer my basic questions.
    which side of the fluid coupling should be the fusible plug, pump or turbine side?
    if the temperature at the hub of the f/c is high is it the indication of bearings failure?
    is there any animation available explaining the functioning of f/c?

  2. #2
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc.

    Conveyor Dynamics Inc.

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    Dear Srikanth:

    I have not bothered to study it. I make a guess, based on the normal circulation of oil in the coupling, the fuse coupling is on the impeller side. Although, I believe the greatest heat might occur after the fluid is sheared. I don't think the difference is significant.
    With the fuse plug on the driving side, driving action is arrested sooner and the rate of fluid pumping out the plug will be greater due to the higher speed (normal circulation = positively powered).

    The flow is toroidal in nature. It passes from the impeller (i=input = motor side) to the runner (r= reducer side). The flow is put in circulation by the impeller, first rotated by the motor, causing centrifugal force on the fluid . The centrifugal force pushes the fluid against the point of lowest pressure which is directly in opposition to its path on the runner side. The turbine blades trap the flow from escaping tangentially or with rotation. Since the impeller (motor) runs faster than the runner ( ie slip occurs as the fluid is sheared across the separation between impeller and runner) the circulation direction is sustained (positively powered or normal circulation). In downhill regenerative drives, the circulation is reversed but I would guess the fuse plug position is not changed.

    The fuse plug is used as protection against overheating and over powering of the coupling fluid due to excessive shearing of fluid in its attempt to transmit more power (kw-hrs = btu's) than it is rated for. Manufacturers' catalogs from Voith, Falk/Sime, ..... will go into better detail on the above description.

    Be careful of the spray!

    Lawrence Nordell
    Conveyor Dynamics, Inc.

  3. Dear Srikant,

    Your enquiry pertains to specific construction detail. I will suggest you to see the fluid coupling manufacturer / supplier's catalogue / leaflet or you can ask it from fluid coupling manufacturer such as Voith Germany which can provide this information and also how various types of fluid coupling operate.
    I have written a book on belt conveyor which also provides good information about functioning of fluid coupling and their overall features / characteristics.

    Generally, fusible plug will be on rotating casing, containing oil, and attached to motor side (but depends on specific make).

    I G Mulani.
    Author - Engineering Science and Application Design for Belt Conveyors.
    email :

  4. #4


    The FC manufacturer would be the best to tell you the correct location of the fusible plug.

    To prevent fluid loss install a dual contact temperature probe wired to warn at a first preset and then shutdown at second preset. The second setpoint should be about 5% below the fusible plugs melting temperture.

    Gary Blenkhorn

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