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Too high fuel pressure

 
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hansjd(at)online.no
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PostPosted: Fri Oct 15, 2010 3:13 am    Post subject: Too high fuel pressure Reply with quote
Hi all,

On starting my Europa after an idle peiode of two months the fuel pressure went sky high as soon as I switched on the main fuel pump, (10 PSI). When switching on secondary pump the pressure went further up to 15-16 PSi.

My engine is a 914, and the pressure had risen increasingly higher (from normal green indication) - up to 6-7 PSi - during the flight test periode. I suspected the fuel pressure sender/instrument to be at fault, but after connecting an auxilliary pressure instrument to the Fuel Pressure Indicator it confirmed the high pressure. So instrument snag is ruled out.

I disconnected the fuel return and connected a hose to let return fuel into a can and all indications went back into the green band when switching on the main. On switching both pumps on there was no further pressure increase - which is normal with my in-series system.(The flow into the can was surprisingly high - 20 liters in 7- 8 minutes!)

Suspecting a clogged fuel return I blew through the return hose - and we could clearly hear bubbling fuel from the tank opening. Now, this should indicate that the return is functioning ok, or????
But when fitting the fuel return again: same high indications.

Now I'm running out of ideas - and to all you wizards out there: Can it be the Fuel Pressure Regulator which is at fault?

By the way: The engine starts and run beautifully and there is no dripping or other indications which should indicate override of the float valve of the carburetors.

Any one been there?? Ideas greatly appreciated!

Cheers
Hans, LN-HJD, #334







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brian.davies(at)clara.co.
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PostPosted: Fri Oct 15, 2010 5:46 am    Post subject: Too high fuel pressure Reply with quote
I have a very different setup to yours (Rotax 912S) but I have had indications of high fuel pressure recently with no other adverse sysmptoms. I found I had a high resistance connection to the fuel pressure transmitter. Wiggled the connector (spade type) and the problem went away.

Regards

Brian Advies

From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of Hans J. Danielsen
Sent: 15 October 2010 11:20
To: europa-list(at)matronics.com
Subject: Too high fuel pressure

Hi all,

On starting my Europa after an idle peiode of two months the fuel pressure went sky high as soon as I switched on the main fuel pump, (10 PSI). When switching on secondary pump the pressure went further up to 15-16 PSi.

My engine is a 914, and the pressure had risen increasingly higher (from normal green indication) - up to 6-7 PSi - during the flight test periode. I suspected the fuel pressure sender/instrument to be at fault, but after connecting an auxilliary pressure instrument to the Fuel Pressure Indicator it confirmed the high pressure. So instrument snag is ruled out.

I disconnected the fuel return and connected a hose to let return fuel into a can and all indications went back into the green band when switching on the main. On switching both pumps on there was no further pressure increase - which is normal with my in-series system.(The flow into the can was surprisingly high - 20 liters in 7- 8 minutes!)

Suspecting a clogged fuel return I blew through the return hose - and we could clearly hear bubbling fuel from the tank opening. Now, this should indicate that the return is functioning ok, or????
But when fitting the fuel return again: same high indications.

Now I'm running out of ideas - and to all you wizards out there: Can it be the Fuel Pressure Regulator which is at fault?

By the way: The engine starts and run beautifully and there is no dripping or other indications which should indicate override of the float valve of the carburetors.

Any one been there?? Ideas greatly appreciated!

Cheers
Hans, LN-HJD, #334







[quote]

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jan_de_jong(at)casema.nl
Guest
PostPosted: Sat Oct 16, 2010 4:43 pm    Post subject: Too high fuel pressure Reply with quote
From your description I would still suspect the return line. Is there a
1-way valve in there?
A way to test it would be to connect the forward line (from the pumps)
directly to the return line using a T-piece with the differential
pressure measurement moved to between the 3rd leg of the T and the
airbox. Run a pump, then both pumps, and see the lowest differential
pressure the regulator can be expected to provide. If it is over 5 psi
it is out of Rotax spec and the return line needs repair.
It could be a very improvised connection - it should only have to deal
with a gauge pressure of 5 psi.
On the other hand, with a completely closed return line a pump delivers
1.8 bar (26 psi). And both in series 3.6 bar (53 psi).
In that case you can make it a very short test.
At zero pressure the pumps are rated to supply 120 l/h. I have heard
that the pumps tend to get better with use. Maybe the improvement to
your current 160 l/h is making it apparent that the return line is too
restrictive.

Regards,
Jan de Jong

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hansjd(at)online.no
Guest
PostPosted: Sun Oct 17, 2010 2:21 am    Post subject: Too high fuel pressure Reply with quote
Thank you Jan for your good advice! I'll lokk into the problem on Monday.

Ragards
Hans
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ptag.dev(at)tiscali.co.uk
Guest
PostPosted: Sun Oct 17, 2010 5:42 am    Post subject: Too high fuel pressure Reply with quote
Hi! Hans.
Early Rotax/912 Europa aircraft instructions were to fit a restrictor in the
return line. This was a simple plug with a fine bore hole in it, they even
provided the plug.
I don't know the origin of your aircraft or fuel system but I do know that
this restrictor is not required in the 914 system.
Check out your installation as to if it has the restrictor in it? They were
simply held in place by a jubilee clip clamping it in place. I have heard of
such restrictors just buggering off down the line after the clips have
relaxed.
Check that out too.
Regards
Bob Harrison. G-PTAG

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