New fuel pump
in 912 / 914 Technical Questions
14 years ago
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by Björn Lindqvist » 12 years ago
Permissible movement of the diaphragm inside the new pump is approx 4-5 mm compared to the older pumps with approx 10 mm. (The diameter of the diaphragm on the new pump is also smaller compared to the older pumps.) It's Important that the pump shaft rests against the cam without being compressed too much when the pump cam stays in the inner position. A compressed pump shaft during this stage will reduce the pumps capapacity (teor about 20%/mm). We have done some tests by adjusting the pump position by adding extra gaskets between the gear box and fuel pump. It was a remarkably good result with 2 extra gaskets, both during climb att 100% and during recovery of pressure after electric pump switch off.
(The above is only a presentation of test results. It's not a proposal for modification.
I apologize for bad English)
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by alessandro pezzola » 12 years ago
hi Bjorn,
it seems that your test suggest an aspiration problem inside the pump: at take of and climbs the pump has difficulties to suck enough fuel, viceversa in prolonged descent,like in finals,the pump has a lot of fuel and the pressure rises...why dont we all go back to our old Pierburg pump????
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by Björn Lindqvist » 12 years ago
Yes, it seems to be some issues about the new pump.
I would not complain if the new pump had greater displacement.
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by Kenneth Hagesten » 12 years ago
Hi Björn
I am flying a Rans S-6 with 80 hp UL engine, and it has worked fine with the older fuel pumps. The Rotax SI is only a recommendation to switch to this new pump. I am not going to replace my older fuel pump until after five years operation, and i have 4 years left.
One thing i and a few fellow pilots have pondered over is if the fuel pump with a malfunction can totally shut the fuel off. Or is it so that the fuel pump ALWAYS lets the fuel go trough even if it malfunctions. Example you have a high winged aircraft and/or a extra electric pump.
If it is so i will not replace my old pump with the new pump as Rotax SI recommends.
Tacksam för svar ifall du vet något om detta.
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by Björn Lindqvist » 12 years ago
Hej Kenneth,
The new fuel pump has never blocked the fuel flow according to our experience.
We have studied the pump parts quite well and the pump's ability to block the fuel flow is very unlikely in my opinion.
We haven't experienced any pump failures, only anomalies in function or performance degradation.
Björn
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