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Rotax 912 pump bypass

in 912 / 914 Technical Questions 13 years ago

  • Re: Rotax 912 pump bypass

    by » 13 years ago

    The engine pump on my 912ULS is one of those made by AC (the last manufacturer to be used by Rotax prior to the new pump that has just come out). It would be surprising if Rotax were to design their new pump to have less flow-through capability than the AC one --- but the only real way to know the answer is to run a flow-through test. Personally, I would rather do this and find if I actually needed to install a bypass.

    A bypass checkvalve is a simple thing that is normally reliable and lasts a long time. However, it is one more possible point of failure --- even if that is a low probability --- and extra weight and complexity --- so I would only install this if the flow-through test showed it to be necessary.

    BTW, if doing a flow-through test the usual safeguards should apply e.g. earthing the aircraft to a metal pole in the ground ( a hanger metal column, for example) and a fire extinguisher nearby.

    Regards, Douglas N
    Thank you said by: Jez O'Hare
      
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  • Re: Rotax 912 pump bypass

    by » 13 years ago

    Thank you, sorry to bother you with another question :

    In the 912 installation manual it shows the electric pump is after the gascolator.. On my trike there is limited space and will be very hard to do this - I was wondering if it would be ok to install the electric pump before the gascolator? My friend said not to do this as it could push water up the line?

    Many thanks if you have any advice on this :)
      
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  • Re: Rotax 912 pump bypass

    by » 13 years ago

    Jez,

    Ideally, the fuel and water should go through the gascolator first. This keeps water and trash from the tank going through the pump. Other than that, the location doesn't really make much difference. If the pump is before the gascolator it will push the water to the gascolator. If it is after the gascolator it will pull the water to the gascolator. Either way, the water and trash stops at the gascolator. An inline filter immediately after the fuel tank or the tank fitting with a built in finger filter would stop any trash right at the tank.

    Bill.
    Thank you said by: Jez O'Hare
      
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  • Re: Rotax 912 pump bypass

    by » 13 years ago

    Thanks Bill, what I meant was : could an electric pump before the gascolator 'agitate the trapped water in the gascolator' pushing some water through to the carbs? Thats what my friend was telling me. Are gascolators a guarantee absolutely no water will go through?
      
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  • Re: Rotax 912 pump bypass

    by » 13 years ago

    Jez,

    There is some merit to your friend's theory. The water/fuel mix could be stirred up by the pump before it gets to the gascolator. The Idea behind the gascolator is that the velocity of the fuel moving through the fuel line drops drastically as it enters the the bowl, allowing the water to drop out of the fuel. Because of the velocity drop, the water cannot be lifted up to the filter screen. The fine mesh screen in the top will stop any small water droplets from passing through. There is no guarantee no water will get through. You should always check for water in the gascolator during the preflight and occasionally remove the carb bowls and check for water. For all practical purposes however, the gascolator is going to remove the water no matter which side the pump is on. Having the pump on the wrong side of the gascolator is preferable to not having an electric pump or not having a gascolator.

    Bill.
    Thank you said by: Jez O'Hare
      
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