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Rotax 912 fuel pump

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klaus(at)utdallas.edu
Guest

Posted: Wed May 21, 2008 10:48 am Post subject: Rotax 912 fuel pump

Hi,



We just learned the hard way that a fuel filter immediately ahead of the 

Rotax mechanical

fuel pump is very important. When we first installed the engine, we did 

have such a filter

to catch initial debris possibly coming from the center tank. That tank 

receives all fuel

from the two wing tanks, which have filters ahead of the electric 

transfer pumps.

After 100 hrs of flying, we thought that the filter ahead of the Rotax 

pump could be

removed, since all fuel comes from the wing tanks and thus is filtered. 

WRONG!

The Rotax pump failed after 400 hrs, gradually losing pressure. The 

second Rotax pump

failed recently, gradually losing pressure after 700 hrs of service. In 

both cases

the electric boost pump saved the day. On the other hand, the three 

facet pumps

used in the system have never failed.



In the repair manual, Rotax warns that the mechanical pump can fail due 

to contamination.

Apparently this can happen even if the fuel sampled from the gascolator 

shows

no contamination, which has been the case for years. We can only conjecture

that the Rotax pump can be disabled by very small debris. The lesson is:

There must always be a filter just ahead of the mechanical pump. Since 

this is in the

engine compartment, the filter must be have a metal housing.



Maybe this will help somebody else avoid the problems and expense we have

had with the Rotax pump.



Happy flying,



Klaus



www.utdallas.edu/~klaus

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haven

Joined: 11 Apr 2007
Posts: 19
Location: Kansas City MO

Posted: Wed May 21, 2008 1:00 pm Post subject: Re: Rotax 912 fuel pump

Is the Rotax pump very costly?

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klaus(at)utdallas.edu
Guest

Posted: Wed May 21, 2008 2:08 pm Post subject: Rotax 912 fuel pump

The most recent cost of the Rotax fuel pump was around $170.



Klaus



www.utdallas.edu/~klaus

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billmileski

Joined: 07 Aug 2006
Posts: 68
Location: Ledyard, CT

Posted: Wed May 21, 2008 7:58 pm Post subject: Re: Rotax 912 fuel pump

Klaus,



Would you happen to know if, when failed, the pump is blocked, or freely allows fuel to still flow through?



Best,



Bill Mileski

701 912S 125hrs

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klaus(at)utdallas.edu
Guest

Posted: Thu May 22, 2008 2:32 pm Post subject: Rotax 912 fuel pump

Hi Bill,



You ask "Would you happen to know if, when failed, the pump is blocked,

or freely allows* *fuel to still flow through?"



The is a short and a long answer. The short answer is that, in the two 

cases

of Rotax pump failure in my plane, the electric boost pump, which is in 

series

and precedes the Rotax pump, managed to pump through the failing

Rotax pump. In both cases, there was a failure of the check valves and

not a diaphram failure, which is nasty indeed, but unlikely to happen

if one replaces the Rotax pump at TBO regardless of whether

one overhauls the engine at that time.



The long answer covers two choices, which are placing the electric boost

pump parallel or in series with the mechanical Rotax pump. Both arrangements

have pros and cons.



Parallel placement:

Either one uses one check valve in each parallel

branch immediately after the electric or mechanical pump. For that

choice, the specter of failing check valves looms.

Or  one omits such check valves and trusts that the internal  check

valve in the electrical pump holds while the

mechanical pump is working, and that the mechanical pump will

retain its internal check valve function even when it fails otherwise.

In my opinion, if I went for the parallel placement choice,

I would go with the choice of two check valves.



Series placement: One trusts that the electric valve will not somehow

become internally clogged and prevent the mechanical pump from

getting fuel, and one also trusts that in case of mechanical pump failure

the electric pump will still be able to pump through the mechanical

pump.



In our installation we opted for the series placement choice. It is

the simplest arrangement, and when one argues through the two possible

types of pump failures (diaphram failure versus check valve failure),

then it seemed to us that series arrangement is likely to save the day 

in case

of pump failure. But this is a matter of opinion, and everybody must

make his/her own decision for this important choice.



Happy flying,



Klaus



klaus(at)utdallas.edu

www.utdallas.edu/~klaus

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professor71(at)HOTMAIL.CO
Guest

Posted: Thu May 22, 2008 7:30 pm Post subject: Rotax 912 fuel pump

Hi Klaus



What kind of fuel filter and how many psi pump do you use? Where, how did you mount your pump? Do you use the filter in conjunction with a gascolator? I have only been relying on the mechanical pump in my 601HD but would like to install a backup electric pump just for such situations as you encountered. 

Thanks

John



[quote] Date: Thu, 22 May 2008 17:28:16 -0500

 From: klaus(at)utdallas.edu

 To: Zenith-List(at)matronics.com

 Subject: Re: Rotax 912 fuel pump

 

 --> Zenith-List message posted by: Klaus Truemper <klaus(at)utdallas.edu>

 

 Hi Bill,

 

 You ask "Would you happen to know if, when failed, the pump is blocked,

 or freely allows* *fuel to still flow through?"

 

 The is a short and a long answer. The short answer is that, in the two 

 cases

 of Rotax pump failure in my plane, the electric boost pump, which is in 

 series

 and precedes the Rotax pump, managed to pump through the failing

 Rotax pump. In both cases, there was a failure of the check valves and

 not a diaphram failure, which is nasty indeed, but unlikely to happen

 if one replaces the Rotax pump at TBO regardless of whether

 one overhauls the engine at that time.

 

 The long answer covers two choices, which are placing the electric boost

 pump parallel or in series with the mechanical Rotax pump. Both arrangements

 have pros and cons.

 

 Parallel placement:

 Either one uses one check valve in each parallel

 branch immediately after the electric or mechanical pump. For that

 choice, the specter of failing check valves looms.

 Or  one omits such check valves and trusts that the internal  check

 valve in the electrical pump holds while the

 mechanical pump is working, and that the mechanical pump will

 retain its internal check valve function even when it fails otherwise.

 In my opinion, if I went for the parallel placement choice,

 I would go with the choice of two check valves.

 

 Series placement: One trusts that the electric valve will not somehow

 become internally clogged and prevent the mechanical pump from

 getting fuel, and one also trusts that in case of mechanical pump failure

 the electric pump will still be able to pump through the mechanical

 pump.

 

 In our installation we opted for the series placement choice. It is

 the simplest arrangement, and when one argues through the two possible

 types of pump failures (diaphram failure versus check valve failure),

 then it seemed to us that series arrangement is likely to save the day 

 in case

 of pump failure. But this is a matter of opinion, and everybody must

 make his/her own decision for this important choice.

 

 Happy flying,

 

 Klaus

 

 klaus(at)utdallas.edu

 www.utdalla========================Change the world with e=EML_WL_ChangeWorld' target='_new'>Join the i’m Initiative from Microsoft.  [quote][b]

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klaus(at)utdallas.edu
Guest

Posted: Fri May 23, 2008 10:44 am Post subject: Rotax 912 fuel pump

Hi John,*



*1. Any decent metal automotive fuel filter will do.



2. According to the Rotax manual, max pressure of the

backup pump should not exceed 5.8 psi.

A good choice is the Facet pump #4015.

Aircraft Spruce offers this pump. There is also another

Facet pump that goes up to 6 psi. Do NOT install that pump

since it exceeds the Rotax psi limit.



3. We mounted the Facet pump on the firewall

downstream from and a bit higher than the gascolator.



4. Our gascolator is just an aluminum box with a quick drain.

It was part of the kit and does not have a screen.



5. Our arrangement is as follows:

gascolator -> filter -> Facet pump -> Rotax pump

There are other arrangements possible. Some aspects were

covered earlier (series versus parallel).



6. A backup pump can be a grief- or even life-saver.



Happy flying,



Klaus



-- 

Klaus Truemper

Professor Emeritus of Computer Science

University of Texas at Dallas

Erik Jonsson School of Engineering and

  Computer Science EC31

P.O. Box 830688

Richardson, TX 75083-0688

(972) 883-2712

klaus(at)utdallas.edu

www.utdallas.edu/~klaus

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