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Fuel flow transducer before or after vapor lock?

in General Tech Discussion 9 years ago
Hi. I have to install fuel flow transduce (FT60). On FT-60 diagram I can read that it should be after vapor lock valve. It's logic, because then it will not computer fuel that went back to tank.

In C42 Ikarus manual I can see that fuel flow should be before vapor lock. In this application I get bed readings.

Where I should to put this? If putting FT60 after valve (fuel pump, vapor lock, then FT60) can make any bad, for example decrease effectivity of vapor lock?

  • Re: Fuel flow transducer before or after vapor lock?

    by » 9 years ago

    Typically the transducer goes on the intake fuel line and not the pressure side out. There should be a fuel filter somewhere before the transducer and the line should be straight before and after the transducer. If the transducer is on the intake line then it is before the recirculation line and if placed in the proper place will not be any place subjected to any vapor lock.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Fuel flow transducer before or after vapor lock?

    by » 9 years ago

    Yes, but i some of plane I saw that transducer is after the pump and T splitter with vapor lock restrictor.
    It's works fine, indications are accurate. Anyway I saw diagrams that shows to do this like that. I'm only not sure how it affect vapor lock system. FT60 is wide opened transducer, without restrictors inside.
      
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  • Re: Fuel flow transducer before or after vapor lock?

    by » 9 years ago

    Producent of the plane have for example this type of diagram.
    Zrzutekranu2015-04-5o09.08.47.png (You do not have access to download this file.)
      
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  • Re: Fuel flow transducer before or after vapor lock?

    by » 9 years ago

    Can somebody explain how this system works?
    Is the "6mm metal T restrictor" a 6mm T with the branch to the tank having a restricting orifice in it allowing a small flow of gasoline (plus any vapor) to return to the tank?
    Mike G
      
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  • Re: Fuel flow transducer before or after vapor lock?

    by » 9 years ago

    If you put the xducer in the intake line it measures total fuel flow, including what returns to tank thru the bypass orifice, which then gives an inaccurate reading (too high). Some folks use two xducers, one in the intake and the other in the bypass line and program the readout to subtract the bypass flow. This doubles the cost and complexity of the system. Most folks, including me, just use one xducer in the intake line and then calibrate the "K" factor to make it read true fuel flow used. This is not quite as accurate as the two xducer method because it will be accurate at only one engine rpm. However if you do the "K" calibration at your normal cruise rpm the accuracy will be right on where it counts. I have been running this way for two years now and find it to be quite accurate. My xducer is mounted inside the cockpit away from engine heat and vibration.

    The other choice is to put it in the pressure line after the bypass tee to get perfect accuracy. The downside of this is you will probably have to mount the unit on the engine subject to heat and vibration-not good for long life of the xducer.
    Thank you said by: Rhett Mitchell
      
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