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Rotax 912ULS Low Fuel Pressure

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arwel.pritchard(at)powerc
Guest

Posted: Wed Apr 21, 2021 2:47 pm Post subject: Rotax 912ULS Low Fuel Pressure

Good Evening



I noticed something strange this evening asI was climbing out at full 

power, when I got to about 1000ft, I switched the electric fuel pump off 

and the fuel pressure dropped quite alarmingly from about 0.32bar to 

below 0.2bar. When I noticed it, I immediately switched the electric 

pump back on to restore the pressure. I then leveled off, reduced power 

and flew a tight circuit back to land.



After landing, I monitored the pressure at various power levels (with 

mechanical pump only) and saw the pressure was at around 0.3bar 

continuously.



I have seen it posted on various forums that its 'one of those things' 

and its nothing to worry about, but I do!!



I should also mention that Im seeing the pressure on a mechanical gauge 

as opposed to an electrical display readout.



Has anybody else come accross this before and is it a real problem?

Thanks



Arwel



G-BYPM

peterz(at)zutrasoft.com
Guest

Posted: Wed Apr 21, 2021 2:58 pm Post subject: Rotax 912ULS Low Fuel Pressure

What I notice is that when the electric pump is shut off, the pressure does drop to near zero, but recovers within about 5 seconds back to the normal 5-7psi.



 	  Quote: 	
		  From my research, this type of intermittent drop is acceptable when the series boost pump is turned off.


	


Cheers,

Pete



 	  Quote: 	
		   On Apr 21, 2021, at 6:55 PM, arwel pritchard <arwel.pritchard(at)powercom.ltd.uk> wrote:

 

 

 

 Good Evening

 

 I noticed something strange this evening asI was climbing out at full power, when I got to about 1000ft, I switched the electric fuel pump off and the fuel pressure dropped quite alarmingly from about 0.32bar to below 0.2bar. When I noticed it, I immediately switched the electric pump back on to restore the pressure. I then leveled off, reduced power and flew a tight circuit back to land.

 

 After landing, I monitored the pressure at various power levels (with mechanical pump only) and saw the pressure was at around 0.3bar continuously.

 

 I have seen it posted on various forums that its 'one of those things' and its nothing to worry about, but I do!!

 

 I should also mention that Im seeing the pressure on a mechanical gauge as opposed to an electrical display readout.

 

 Has anybody else come accross this before and is it a real problem?

 

 

 Thanks

 

 Arwel

 

 G-BYPM

Griffo

Joined: 18 Mar 2021
Posts: 70
Location: The Oaks, NSW, Australia

Posted: Wed Apr 21, 2021 3:31 pm Post subject: Re: Rotax 912ULS Low Fuel Pressure

I have been through almost the same process - in the end borrowed a "Master Gauge" -  with it, I found that the fuel pressure remained, at all times, within Rotax specifications - suggest you do the same.

_________________
46

budyerly@msn.com

Joined: 05 Oct 2019
Posts: 286
Location: Florida USA

Posted: Wed Apr 21, 2021 4:40 pm Post subject: Rotax 912ULS Low Fuel Pressure

Arwel,

Pressure senders differ.  When a rapid change occurs, they tend to lag or even fluctuate for a moment.  Bench test is the only way to assure yourself of what is going on.  Normally a momentary change in flow or pressure causes lights to flash and all kinds of exciting things.  Every manufacturer has a smoothing method to prevent rapid needle or digit fluctuation.  They are all annoying.



Most gauges and senders have their own idiosyncrasies. Normally a direct reading fuel pressure has a very small orifice to dampen the gauge.  If the gauge hookup is teed into a line, the change in flow/pressure rapidly changes the direct reading gauge.  It is that damned Italian Bernoulli to blame.  We forget that pressure and flow are related.  Change either and the other is quickly affected.  Put in a bleed orifice like the FS02 and that too affects the momentary pressure/flow.  



Sounds like you tested it out on the ground and all's well.



Gauges moving up and down after any change don't excite me unless I hear, see, feel other changes.  Sudden quiet does bother me though.



Best Regards,

Bud Yerly



--

IanCook_1(at)hotmail.com
Guest

Posted: Wed Apr 21, 2021 11:08 pm Post subject: Rotax 912ULS Low Fuel Pressure

Check your fuel filters for contamination.



Ian



--

SteveIvell(at)pestproof.c
Guest

Posted: Thu Apr 22, 2021 12:25 am Post subject: Rotax 912ULS Low Fuel Pressure

Apparently it's a known "phenomenon" .



Kind Regards



Steve Ivell



--

Peter jeffers

Joined: 24 Aug 2020
Posts: 20
Location: hp143hr

Posted: Thu Apr 22, 2021 12:40 am Post subject: Rotax 912ULS Low Fuel Pressure

Hi ARWEL,

What you are seeing is quite normal. If you have the nerve wait a few seconds (and I do mean seconds) without switching on the electric pump and you will find the pressure indication recovers. 

Read what Bud says. Only investigate further if the pressure does not recover or anything else exciting happens.

Pete



--

_________________
Pete

Dave Disney

Joined: 16 Aug 2010
Posts: 54
Location: Weston-Super-Mare

Posted: Thu Apr 22, 2021 8:34 am Post subject: Re: Rotax 912ULS Low Fuel Pressure

As a matter of interest I seem to remember reading that on the RV12 they leave the electric fuel pump 'on' all the time. I now do this and only turn it off at height to check that the mechanical pump is working properly. My low pressure warning light flickers for a few seconds then remain off. I then switch the electric fuel pump back on again.



My reasoning for this is that the electric pump is a low cost item when it comes to replacement, it will help avoid any problems with vapor lock and is one less thing to worry about pre take-off and landing (although I still check that it's on).

Griffo

Joined: 18 Mar 2021
Posts: 70
Location: The Oaks, NSW, Australia

Posted: Thu Apr 22, 2021 7:19 pm Post subject: Re: Rotax 912ULS Low Fuel Pressure

Hi Dave,



Hi,



It’s good that you are taking precautions to avoid having the electric (boost/back up) pump mask/hide a failed mechanical fuel pump.

However, I would question the merit of leaving your electric pump on at all times, as I would expect a pump, so operated, to become a service item replaced at ?? hours of operation (as the mechanical pump has a recommended service life).

I only use my electric pump – prior to engine start (off for start) to check fuel pressure/availability. On again, for take-off. Off when safe height above terrain achieved. On again, when downwind for landing.

Your engine will run perfectly without the need for the electric pump, which should only be used when you have a mechanical fuel pump failure, at critical times, when fuel starvation is not a good option.

_________________
46

jeffwill55(at)sbcglobal.n
Guest

Posted: Fri Apr 23, 2021 12:23 pm Post subject: Rotax 912ULS Low Fuel Pressure

This has caused me to think a bit.



The Europa builder’s manual shows the fuel going from the fuel selector to the electric fuel pump and then to the engine’s mechanical fuel pump. Is that how it is set up? 



If so, does the fuel get pulled through the electric fuel pump by the mechanical fuel pump when the electrical fuel pump is turned off? That seems like it would cause variation at that point.



Various aircraft builder’s books from the EAA show a parallel system for low-wing aircraft. Those diagrams make sense to me. In other words, they show the fuel being provided by a parallel fuel system, with fuel lines going from the fuel selector to both 1) the electric fuel pump and then to the carb, and  2) to the engine’s mechanical fuel pump and to the carb. 



That way, if the mechanical pump quits, the electrical pump doesn’t have to try to push fuel though the mechanical one to get to the carb. And, the mechanical pump doesn’t have to pull fuel through the electric fuel pump if the electric fuel pump is off or it quits.



Which way should this be set up, and and if you think it’s the way shown in the Europa builder’s manual, why?



Jeff Williams

Builder A157

 	  Quote: 	
		  On Apr 22, 2021, at 10:19 PM, Griffo <scangriffin(at)bigpond.com.au (scangriffin(at)bigpond.com.au)> wrote:

--> Europa-List message posted by: "Griffo" <scangriffin(at)bigpond.com.au (scangriffin(at)bigpond.com.au)>Hi Dave,Hi,Itâs good that you are taking precautions to avoid having the electric (boost/back up) pump mask/hide a failed mechanical fuel pump.However, I would question the merit of leaving your electric pump on at all times, as I would expect a pump, so operated, to become a service item replaced at ?? hours of operation (as the mechanical pump has a recommended service life).I only use my electric pump â prior to engine start (off for start) to check fuel pressure/availability. On again, for take-off. Off when safe height above terrain achieved. On again, when downwind for landing.Your engine will run perfectly without the need for the electric pump, which should only be used when you have a mechanical fuel pump failure, at critical times, when fuel starvation is not a good option.--------46Read this topic online here:http://forums.matronics.com/viewtopic.php?p=501476#501476

peterz(at)zutrasoft.com
Guest

Posted: Fri Apr 23, 2021 12:42 pm Post subject: Rotax 912ULS Low Fuel Pressure

Fwiw, mine was pulling through the elec fuel pump, but I have re-hosed it and now added an andair checkvalve in parallel with the pump. Common practice, and removes any fuel pump restriction.



Will be interesting to see if that change reduces the drop.

Cheers

PeteZ



On Fri., Apr. 23, 2021, 4:30 p.m. Jeffrey Williams, <jeffwill55(at)sbcglobal.net (jeffwill55(at)sbcglobal.net)> wrote:



 	  Quote: 	
		  This has caused me to think a bit.

The Europa builder’s manual shows the fuel going from the fuel selector to the electric fuel pump and then to the engine’s mechanical fuel pump. Is that how it is set up? 

If so, does the fuel get pulled through the electric fuel pump by the mechanical fuel pump when the electrical fuel pump is turned off? That seems like it would cause variation at that point.

Various aircraft builder’s books from the EAA show a parallel system for low-wing aircraft. Those diagrams make sense to me. In other words, they show the fuel being provided by a parallel fuel system, with fuel lines going from the fuel selector to both 1) the electric fuel pump and then to the carb, and  2) to the engine’s mechanical fuel pump and to the carb. 

That way, if the mechanical pump quits, the electrical pump doesn’t have to try to push fuel though the mechanical one to get to the carb. And, the mechanical pump doesn’t have to pull fuel through the electric fuel pump if the electric fuel pump is off or it quits.

Which way should this be set up, and and if you think it’s the way shown in the Europa builder’s manual, why?

Jeff Williams

Builder A157

 	  Quote: 	
		  On Apr 22, 2021, at 10:19 PM, Griffo <scangriffin(at)bigpond.com.au (scangriffin(at)bigpond.com.au)> wrote:



--> Europa-List message posted by: "Griffo" <scangriffin(at)bigpond.com.au (scangriffin(at)bigpond.com.au)>



Hi Dave,



Hi,



Itâ€™s good that you are taking precautions to avoid having the electric (boost/back up) pump mask/hide a failed mechanical fuel pump.

However, I would question the merit of leaving your electric pump on at all times, as I would expect a pump, so operated, to become a service item replaced at ?? hours of operation (as the mechanical pump has a recommended service life).

I only use my electric pump â€“ prior to engine start (off for start) to check fuel pressure/availability. On again, for take-off. Off when safe height above terrain achieved. On again, when downwind for landing.

Your engine will run perfectly without the need for the electric pump, which should only be used when you have a mechanical fuel pump failure, at critical times, when fuel starvation is not a good option.



--------

46





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=501476#501476

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