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fuel line bubbles-Follow up

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rrhoyt(at)ieee.org
Guest

Posted: Fri Feb 24, 2006 5:08 am Post subject: fuel line bubbles-Follow up

A couple of weeks ago I inquired about fuel line bubbles.  I got some 

good perspective from the list.



I reviewed the Rotax service bulletin on 912F fuel pumps and 

determined that the fuel pump met the inspection test and the 

pressure test.  The fuel lines, filled with fuel, maintained a 5 psi 

pressure for half an hour after pressurizing.  (No additional 

pressurization after the initial pumping.)  I replaced the fuel line 

riser section with clear tubing and watched the engines pump draw 

fuel without bubbles. The fuel had small bubbles at the input to the 

carburetor. They appeared to be the result of trapped air in the 

clear tube connection to the fuel system.



I never did a vacuum test.  It might have exposed the failure 

mode.  By replacing the riser section with aluminum tubing and  short 

flexible couplings to the pump and off the engine to the plane I 

seemed to have remove the preponderance of the bubbles.  In the 

process of removing the neoprene tubing from the fuel pump I found 

that it could be turned and pulled off without loosening the 

clamp.  It did not leak during the pressure testing, however!



I concluded that The neoprene tubing was collapsing and or air was 

being drawn in through the loose clamp due to the vacuum exacerbated 

by the collapsed tubing.



The plane flew today without flashing alarms.  The nominal fuel 

pressure was greater than 4 psi and never lower.



I'm posting this follow up for anybody in the future who discovers 

bubbles in their fuel line.



Thanks for the help

Ron



At 10:13 AM 2/13/2006, you wrote:

 	  Quote: 	
		  



If you have bubbles in the fuel lines the first thing I would do is a vacuum

test.    Close off the supply and put a vacuum on the line going to the

carbs,, next do a pressure test,  because of the directional valves in the

fuel pump you will have to apply the pressure from the tank side of the

pump.



Next compare the pressure on your pump to the pressure the pump should

provide..



Boyd

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Fri Feb 24, 2006 7:46 am Post subject: fuel line bubbles-Follow up

I have never yet found a store-bought clamp that I thought was worth a 

flip on clear tubing.

If you are using clear tubing, then make your own fuel line clamps from 

safety wire.

Here is how to do it:

http://www.bcchapel.org/pages/0003/pg13.html

Scroll to the bottom of the page.



Richard Pike

MKIII N420P (420ldPoops)

Ron Hoyt wrote:

 	  Quote: 	
		   



 A couple of weeks ago I inquired about fuel line bubbles.  I got some 

 good perspective from the list.

   

<snip>
	


 	  Quote: 	
		    In the 

 process of removing the neoprene tubing from the fuel pump I found 

 that it could be turned and pulled off without loosening the 

 clamp.  It did not leak during the pressure testing, however!



 I concluded that The neoprene tubing was collapsing and or air was 

 being drawn in through the loose clamp due to the vacuum exacerbated 

 by the collapsed tubing.



   

<snip>

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

flht99reh(at)netzero.net
Guest

Posted: Fri Feb 24, 2006 10:25 am Post subject: fuel line bubbles-Follow up

Ah Richard, your site is a veritable garden of fruitful wisdom and I have

always enjoyed your one liner: "ask me how I know this". The wire wrap is a

natural and is far better than a hose clamp as the wire goes in-between the

barbs where the hose clamp simply straddles the barbs. But that homemade

gasolater looks to be a considerable amount of work. But having more time

than money myself, I may give this greater consideration. Do you have a part

number for the filter? Thanks for the info.



Wiser Ralph of Ohio



--

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Fri Feb 24, 2006 11:37 am Post subject: fuel line bubbles-Follow up

Richard,



For those who have not yet used safety wire for hose clamps.



I've used safety wire to clamp hoses like this too, and it works fine 

if done right, per your suggestion. The first time I did it, the wire 

cut the hose because the safety wire was too thin, so I recommend using 

heavier rather than lighter safety wire, as your pictures show. The 

thicker wire is less prone to cutting into the tubing.



Thom in Buffalo

do not archive

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Thom Riddle
Buffalo, NY (9G0)

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Larry Cottrell

Joined: 10 Jan 2006
Posts: 35
Location: Klamath Falls, Oregon

Posted: Fri Feb 24, 2006 3:43 pm Post subject: fuel line bubbles-Follow up

---

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jbhart(at)onlyinternet.ne
Guest

Posted: Fri Feb 24, 2006 4:42 pm Post subject: fuel line bubbles-Follow up

At 10:45 AM 2/24/06 -0500, you wrote:

 	  Quote: 	
		  



I have never yet found a store-bought clamp that I thought was worth a 

flip on clear tubing.

If you are using clear tubing, then make your own fuel line clamps from 

safety wire.

Here is how to do it:

http://www.bcchapel.org/pages/0003/pg13.html

Scroll to the bottom of the page.



Richard Pike

MKIII N420P (420ldPoops)




	


Kolbers, 



To save weight, I use Richard's safety wire clamps on all fuel line 

connections.  In my case I put on two clamps side be side, so that if one 

fails there is a second clamp.  The trick is to twist the wire until the 

safety wire has about one half the wire thickness pressed into the tubing.  

So far, I have not had one fail.



Jack B. Hart FF004

Winchester, IN



do not archive

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Fri Feb 24, 2006 4:45 pm Post subject: fuel line bubbles-Follow up

You are too kind. Unfortunately, I do not have a part number, the one in 

the pictures was chosen by going to the rotating rack at Advance Auto 

Parts, twirled it until I saw one that looked good, and said

"Hmm - wonder if this one will work?" It took about 40 minutes to do.

Sorry not to be more help.

Richard Pike

MKIII N420P (420ldPoops)

do not archive



flht99reh wrote:

 	  Quote: 	
		   



 Ah Richard, your site is a veritable garden of fruitful wisdom and I have

 always enjoyed your one liner: "ask me how I know this". The wire wrap is a

 natural and is far better than a hose clamp as the wire goes in-between the

 barbs where the hose clamp simply straddles the barbs. But that homemade

 gascolater looks to be a considerable amount of work. But having more time

 than money myself, I may give this greater consideration. Do you have a part

 number for the filter? Thanks for the info.



 Wiser Ralph of Ohio

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Fri Feb 24, 2006 5:06 pm Post subject: fuel line bubbles-Follow up

Actually, that gascolator is something I made to use, and then ended up 

not using it because I installed a different gas tank instead, (with a 

built in water sump to a drain) but I can tell you how I would have done 

it, and based on what I am currently using it which has a quick drain-



Since the gascolator is not heavy you can probably stick it in the fuel 

line at any convenient low point. The L shaped fitting that exits the 

bottom of the gascolator is then plumbed via a flex tube of almost any 

description to a low point and then add in a standard GA drain valve. 

(SAF-AIR, Curtis Push-N"-Twist, etc.)You can also thread the drain valve 

into a standard brass fitting (auto parts store) and solder the fitting 

to a short 1/4'  copper tube which makes it easier to attach to the 

airframe and to the flex line coming from the gascolator.



Richard Pike

MKIII N420P (420ldPoops)

do not archive

Larry Cottrell wrote:

 	  Quote: 	
		   I have a question as well. The gascolater looks to be pretty simple and 

 ingenious, but I was wondering about the method of attachment to the bottom 

 of the plane. The L shaped aluminum fitting that goes into the bottom of the 

 gascolater through the gasket is my point of confusion. I am guessing that 

 they only make them in that configuration, but it seems to complicate the 

 fitting to the plane. If you could elaborate on the attachment to the plane 

 it would help me a great deal. Is the gascolater fastened solidly or 

 floating with a tube going to the drain arrangement? The fitting that opens 

 the gascolater to drain, is that just a petcock arrangement, or is it a 

 standard fuel drain as in G.A.?

 Larry, Oregon

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

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