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Non-return valves

in General Tech Discussion 7 years ago
Just wondering how important it is to fit non-return valves on 914 engines fuel lines considering that they run two electric fuel pumps into a "T" junction before the regulator.
Should they be mandatory???

  • Re: Non-return valves

    by » 7 years ago

    Are you reading the 914 installation manual? (Page 84.)

    The pumps are in series, The Non-Return Valves are installed as By-Pass Valves and are absolutely mandatory.
    One is open at all times.
    The Tee should be AFTER the Fuel pressure regulator.

    What Installation is this?

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Rick Elliott
      
    Report

  • Re: Non-return valves

    by » 7 years ago

    The "T" I am referring to is the junction of the two pumps which I believe should be before the regulator. The installation is in a gyrocopter.
    The manufacturer has said that non-return valves are not mandatory.
      
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  • Re: Non-return valves

    by » 7 years ago

    Hi Rick,

    There have been many aircraft Mfg's. that have been wrong and caused a lot of their own problems. Even if it isn't mandatory best practice and info right out of the Rotax installation manual say different.

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

      
    Report

  • Re: Non-return valves

    by » 7 years ago

    +1 to Roger,

    If your Pumps are plumbed in parallel, you have a problem.
    They should be plumbed in SERIES as shown in the installation manual.
    When you turn ON both parallel pumps at the same time, fuel flow rates double and you risk overwhelming the fuel regulator and tank return line.

    The 914 pumps do not permit reverse flow by the nature of their design. Additional Non-Return valves are Not needed.
    The One-Way valves shown in the installation manual act as bypass valves for the pumps.
    When operating with a single pump, the fuel needs to By-Pass the other pump as fuel will not flow through the non-powered pump.

    Note:
    This advice applies to the 914 Medium Pressure(25psi)Turbo Fuel pumps.
    This does NOT apply to 912ul(s) Low pressure(4psi) Fuel Pumps which are of a different design.
    The 912is and the 915 engines use High Pressure(90psi) Fuel Injection pumps and are different from the others.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Rick Elliott
      
    Report

  • Re: Non-return valves

    by » 7 years ago

    Thanks Bill, I am a bit confused though. You said in an earlier post that non-return valves are mandatory but in the most recent post you say that the electric fuel pumps on 914 engines do not allow reverse flow.
    If the pumps don't allow for reverse flow, why would non-return valves be required????
      
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