fbpx

 

Dear All,

I have a technical question regarding the 914 wiring diagram connection and specifically with the main and aux fuel pump.

In accordance to the installation manual the wiring diagram shows the main pump (18) connected directly to a 5A circuit breaker and after to the rectifier while the aux pump (19) connected directly to a 5A circuit breaker on the main bus. None of them use a switch but rather connected respectively to each of the magnetos switch. This will allow both fuel pump to run all the time once the magnetos switches are on the ON position. Is this statement correct? Does the 914 require both fuel pump to be ON all the time during flight? Why there is a main and aux pump if both are used?

I apologize in advance for any misinterpretation and thank you for everybody's input!

Matt  

9051_1_Pages from IM_914 Series_ED3 1.pdf (You do not have access to download this file.)
  • Re: Rotax 914F wiring diagram - fuel pumps

    by » 6 months ago


    Hello,

    can anybody give me some input on the topic above? Thank you very much in advance!


  • Re: Rotax 914F wiring diagram - fuel pumps

    by » 6 months ago


    I have experience with the 912ULS not the 914. If this was my project I would install each pump with its own dedicated switch and fuse or breaker wired to the ON side of the master switch. I would keep them isolated from your ignition switches.


  • Re: Rotax 914F wiring diagram - fuel pumps

    by » 6 months ago


    The Rotax Operator Manual for the 914 advises to use both pumps for takeoffs and landings, and shut off the aux pump at safe altitude. The Operator Manual is available on this website or at the official Rotax website.

    It is best to wire the main pump directly to the generator regulator output, without a switch, making it impossible to accidentally turn off the main pump.

    There is no connection between the mag switches and the fuel pumps.


  • Re: Rotax 914F wiring diagram - fuel pumps

    by » 6 months ago


    Breakers (46) and (47) are assumed to be Switchable Breakers but could also be installed as a separate switch and fuse.
    The Main Fuel Pump(18) is powered directly from the Generator and will remain powered through the breaker(46) as long as the generator operates even if the Generator Relay (58) is de-energized.
    The ALT Pump(19) is powered via the generator or the Battery through Breaker (47).
    This gives the two pumps separate/redundant power sources.

    Under normal flight, either pump can operate the engine singly.
    Operation using only one pump is acceptable once a safe altitude has been reached.
    The term MAIN and AUX is arbitrary. They could have also been labeled 1,2 or Left,Right, or A,B
    - - -

    Emergency landing procedures should include a method of ensuring that both Pumps are de-energized shortly before/after touchdown to ensure that the pumps are not able to continue pumping after impact and feed fuel to any fire.
    - - -

    Confusion ????
    The fuel pumps are not connected to either of the Magneto/Ignition Switches (33)
    Do you mean Master Switch(34) ?


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: Rotax 914F wiring diagram - fuel pumps

    by » 6 months ago


    Hello Bill,

    first at all thank you for your reply! Yes you are correct both fuel pumps are connected to the Master Switch (34) and not the magnetos switches. With that being said I still do not understand why they do not show switches on the diagram if they are required. I understand your statement "are assumed to be switchable breaker" but technically speaking there should be no assumption in aviation also considering that 46 and 47 are called specifically "circuit breakers" just like all the other circuit breakers on the same diagram. So if we follow the diagram as is the two pumps are installed without a switch and in order to turn them OFF as you noted in an emergency situation you will have to pull the two breaker. With this configuration you will have both pumps running all the time unless a breaker is pulled, which is totally fine but I just wanted to confirm since it is unusual on an airplane installation. Of course as you stated above the electrical connection of each pump will then assure the functionality of at least one pump in case of an electrical failure.

    At the end I think that a switch for each pump could be installed but realistically it is not necessary and they can be connected using two standard circuit breaker 46 & 47 which can be pulled in case of necessity/emergency. Honestly I think this remove an extra piece in the system (switch) which could potentially fail.

    Feel free to add any comment you may have and thanks again!


You do not have permissions to reply to this topic.