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Fuel boost M vs. R


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Does anyone know why the Ovation has two fuel boost pumps (high and low) while the Bravo only has one?  I flew in my friend's 98 Ovation the other day and noticed the high fuel boost pump switch that had a cover over it, in addition to a fuel boost pump switch just like in my Bravo.  I read in the Ovation POH but only found that it seemed to reduce the amount of priming time needed for a hot start.  I thought that was odd since both of our airplanes were made in 1998.  Thanks for any insight.  

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Yes...

And the M20K has even more options than any other...

There are four different functions that the fuel pump achieves... for the O.

  • It is all one fuel pump...
  • Different rates of delivery...
  • For some Ks... different location of delivery...

The four different functions...

1) Pre-starting fuel delivery... aka priming the fuel system.  Lo or Hi... count the seconds...

2) post starting fuel boost... on cold days. Lo only...

3) Mechanical fuel pump replacement... in the event the mechanical pump goes missing in flight?  Hi only...

4) Max FF when WOT... gets enhanced automatically with the electric fuel pump...

The O has two pump switches that could have been named better...

It sounds like there are two different pumps...  there is only one... Hi boost is about 3X the flow rate of Lo boost...

They both send fuel to the same place...

As the system ages.... the electronic regulator for Lo Boost may need an OH...

The fuel pump and tank selector switches are selected by the engine manufacturer...

The return line from the fuel system back to the tanks is always interesting... for the O, the return is simultaneously switched to the tank it is drawn from... some planes are not that lucky, and always return to one side...

Pre-hot start... fuel is circulated through the system from the tanks to the injection system stopping at the mixture that is at ICO... the warmed fuel heads back to the selector valve and back to the tank it came from...

PP thoughts only not a mechanic...

Best regards,

-a-

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Thanks for the insight.  I was just asking out of pure curiosity.  So why in the same model year would the Ovation have more fuel boost options than the Bravo?  Is there something different about the Continental engine that makes more options necessary?  Overall I thought the Ovation was a simpler plane, no cowl flaps to mess with, no turbocharger to cause problems; however, it seems it has the more complicated fuel delivery system.  Just curious, nothing more.         

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Lycoming vs Continental...

Mooney takes the recommendation from the engine manufacturer and installs it as a whole system... including the selector valve...

Bravo and Ovation probably haven’t changed in this respect from day one...

The M20K changed some detail over time...

The M20C wins the simplicity award... its primer pump is also its accelerator pump... that operates when mechanically / manually pushing the throttle all the way in...  :)

Best regards,

-a-

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Good descriptions! Pretty much have settled on the red switch for 10 seconds of prime for cold starts then upon start turn on the black switch till idle is stable and then turn off. 

 

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