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Is check valve in fuel return line needed?

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Martin Pohl

Joined: 30 Jan 2006
Posts: 118
Location: CH-8645 Jona SG, Switzerland

Posted: Sun Dec 16, 2007 9:21 am Post subject: Is check valve in fuel return line needed?

Hi folks



Is there a need for a check valve in the fuel return line (vapour lock return line)? Engine will be the Rotax 912ULS.



Cheers Martin

_________________
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
http://www.pohltec.ch/ZodiacXL/Main.html

gfmjr_20(at)HOTMAIL.COM
Guest

Posted: Sun Dec 16, 2007 11:48 am Post subject: Is check valve in fuel return line needed?

Martin--

    I did not use a check valve on my return line.  There is a restricter in the return line with about a .3mm hole in it so there is not much fuel that flows through the line. The engine end of the line is also significantly higher that the termination at the tank.  I think when I did my fuel flow tests with just the electrical pump on the fuel returned through this line was  about 13 ounces

  

 George May

 601XL 912s 174hours



 	  Quote: 	
		   Subject: Is check valve in fuel return line needed?

 From: mpohl(at)pohltec.ch

 Date: Sun, 16 Dec 2007 09:21:42 -0800

 To: zenith-list(at)matronics.com

 

 --> Zenith-List message posted by: "Martin Pohl" <mpohl(at)pohltec.ch>

 

 Hi folks

 

 Is there a need for a check valve in the fuel return line (vapour lock return line)? Engine will be the Rotax 912ULS.

 

 Cheers Martin

 

 --------

 Martin Pohl

 Zodiac XL QBK

 8645 Jona, Switzerland

 www.pohltec.ch/ZodiacXL

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=152523#152523

 

 

 

 

 > 

 

 


	


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ashontz

Joined: 27 Dec 2006
Posts: 723

Posted: Mon Dec 17, 2007 7:25 am Post subject: Re: Is check valve in fuel return line needed?

What's your reasoning for the return lines? The plans don't call for it, but I was thinking of adding one myself to not burn out the pump with too much pressure.



[quote="gfmjr_20(at)HOTMAIL.COM"]Martin--

    I did not use a check valve on my return line.  There is a restricter in the return line with about a .3mm hole in it so there is not much fuel that flows through the line. The engine end of the line is also significantly higher that the termination at the tank.  I think when I did my fuel flow tests with just the electrical pump on the fuel returned through this line was  about 13 ounces

  

 George May

 601XL 912s 174hours



 	  Quote: 	
		   Subject: Is check valve in fuel return line needed?

 From: mpohl(at)pohltec.ch

 Date: Sun, 16 Dec 2007 09:21:42 -0800

 To: zenith-list(at)matronics.com

 

 --> Zenith-List message posted by: "Martin Pohl" <mpohl>

 

 Hi folks

 

 Is there a need for a check valve in the fuel return line (vapour lock return line)? Engine will be the Rotax 912ULS.

 

 Cheers Martin

 

 --------

 Martin Pohl

 Zodiac XL QBK

 8645 Jona, Switzerland

 www.pohltec.ch/ZodiacXL

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=152523#152523

 

 

 

 

 > 

 

 



	


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Martin Pohl

Joined: 30 Jan 2006
Posts: 118
Location: CH-8645 Jona SG, Switzerland

Posted: Mon Dec 17, 2007 8:32 am Post subject: Re: Is check valve in fuel return line needed?

Hi Andy

 	  Quote: 	
		  What's your reasoning for the return lines? 	
Vapour lock issues - it is e.g. in UK a mandatory modification (http://www.pfa.org.uk/Data%20Sheets/162B%20ZENAIR%20CH601-XL.pdf).



The CZAW plans include the return line. I have a left inner tank with return inlet.



We are using automotive fuel here in Europe (and it is in fact recommended for the Rotax rather than 100LL) which results in higher vapour lock risk.



Cheers Martin

_________________
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
http://www.pohltec.ch/ZodiacXL/Main.html

Last edited by Martin Pohl on Mon Dec 17, 2007 8:39 am; edited 1 time in total

Martin Pohl

Joined: 30 Jan 2006
Posts: 118
Location: CH-8645 Jona SG, Switzerland

Posted: Mon Dec 17, 2007 8:36 am Post subject: Re: Is check valve in fuel return line needed?

(at)George: Thank you for your info! The CZAW plans also don't call for a check valve. And as you said the line is going quite a bit down from the engine to the tank, so there shouldn't be any backpressure from the tank.



Cheers Martin

_________________
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
http://www.pohltec.ch/ZodiacXL/Main.html

Martin Pohl

Joined: 30 Jan 2006
Posts: 118
Location: CH-8645 Jona SG, Switzerland

Posted: Mon Dec 17, 2007 8:50 am Post subject: Re: Is check valve in fuel return line needed?

By the way: here is my "final" fuel system layout, which is apart from the additional left wing fuel pump and the fuel flow meter the standard CZAW fuel setup.



FuelSystem



Cheers Martin

_________________
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
http://www.pohltec.ch/ZodiacXL/Main.html

ashontz

Joined: 27 Dec 2006
Posts: 723

Posted: Mon Dec 17, 2007 8:51 am Post subject: Re: Is check valve in fuel return line needed?

Good to know, I'll probably install a return line myself. What can it hurt. I know all of my cars have a return line, probably for good reason too. Is the return line smaller?



That being the case, I always hear the term vapor lock, in technical terms can someone explain EXACTLY what it is and where in the fuel system it occurs generally for everyone's benefit? I know sometimes my old lawnboy mower won't start after running for awhile and I need to take the air filter off to let it breath better so I can restart it. I assume this is vapor lock, but I'm not really sure. I've never had it stop running, but restarting was a major problem before I replaced the mower due to other problems with the mower being a yardsale total piece of crap I bought when I was poor years ago and not worth fiddling with everytime I wanted to mow the lawn.



 	  Martin Pohl wrote: 	
		  Hi Andy

 	  Quote: 	
		  What's your reasoning for the return lines? 	
Vapour lock issues - it is e.g. in UK a mandatory modification (http://www.pfa.org.uk/Data%20Sheets/162B%20ZENAIR%20CH601-XL.pdf).



The CZAW plans include the return line. I have a left inner tank with return inlet.



We are using automotive fuel here in Europe (and it is in fact recommended for the Rotax rather than 100LL) which results in higher vapour lock risk.



Cheers Martin

Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Mon Dec 17, 2007 9:28 am Post subject: Re: Is check valve in fuel return line needed?

It there for a different reason in your car. Probably because there is a fuel injection system in use.

 	  ashontz wrote: 	
		  Good to know, I'll probably install a return line myself. What can it hurt. I know all of my cars have a return line, probably for good reason too. Is the return line smaller?

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

ashontz

Joined: 27 Dec 2006
Posts: 723

Posted: Mon Dec 17, 2007 9:49 am Post subject: Re: Is check valve in fuel return line needed?

My 1985 Nissan pickup is carburated and it has a return line.



 	  Gig Giacona wrote: 	
		  It there for a different reason in your car. Probably because there is a fuel injection system in use.

 	  ashontz wrote: 	
		  Good to know, I'll probably install a return line myself. What can it hurt. I know all of my cars have a return line, probably for good reason too. Is the return line smaller?

gfmjr_20(at)HOTMAIL.COM
Guest

Posted: Mon Dec 17, 2007 3:12 pm Post subject: Is check valve in fuel return line needed?

The Rotax installation manual suggests a return line and in addition ,since I burn mostly auto fuel, I wanted to insure against vapor lock.

[quote] Subject: Re: Is check valve in fuel return line needed?

 From: ashontz(at)nbme.org

 Date: Mon, 17 Dec 2007 07:25:46 -0800

 To: zenith-list(at)matronics.com

 --> Zenith-List message posted by: "ashontz" <ashontz(at)nbme.org>

 What's your reasoning for the return lines? The plans don't call for it, but I was thinking of adding one myself to not burn out the pump with too much pressure.

 [quote="gfmjr_20(at)HOTMAIL.COM"]Martin--

 I did not use a check valve on my return line. There is a restricter in the return line with about a .3mm hole in it so there is not much fuel that flows through the line. The engine end of the line is also significantly higher that the termination at the tank. I think when I did my fuel flow tests with just the electrical pump on the fuel returned through this line was about 13 ounces

 George May

 601XL 912s 174hours

 > Subject: Is check valve in fuel return line needed?

 > From: mpohl(at)pohltec.ch

 > Date: Sun, 16 Dec 2007 09:21:42 -0800

 > To: zenith-list(at)matronics.com

 > 

 > --> Zenith-List message posted by: "Martin Pohl" 

 > 

 > Hi folks

 > 

 > Is there a need for a check valve in the fuel return line (vapour lock return line)? Engine will be the Rotax 912ULS.

 > 

 > Cheers Martin

 > 

 > --------

 > Martin Pohl

 > Zodiac XL QBK

 > 8645 Jona, Switzerland

 > www.pohltec.ch/ZodiacXL

 > 

 > 

 > 

 > 

 > Read this topic online here:

 > 

 > http://forums.matronics.com/viewtopic.php?p=152523#152523

 > 

 > 

 > 

 > 

 > > 

 > 

 > 

 > 

 > 

 Share life as it happens with the new Windows Live. Share now! 

 > [b]

 --------

 Andy Shontz

 CH601XL - Corvair

 www.mykitlog.com/ashontz

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=152676#152676> 

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bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Mon Dec 17, 2007 7:13 pm Post subject: Is check valve in fuel return line needed?

Vapor lock is what results when the fuel pump is full of fuel vapor (or 

air)instead of liquid fuel. The pump is designed to pump liquid, it 

won't pump vapor worth a damn. It is caused when the fuel in the line 

leading into the pump is vaporized due to excessive heat and/or 

excessive suction on the line. It often results from drawing a suction 

on the fuel line by trying to suck fuel uphill to a hot engine 

compartment because reducing the pressure on the fuel also reduces its 

boiling point. The situation is worse with auto fuel because some of its 

components have a much lower boiling point than anything found in avgas. 

The one of the worst cases is a pump attached to a hot engine on a hot 

day at high altitude sucking fuel from low-wing tanks during a nose high 

maneuver at full throttle and maximum fuel flow (i.e. just after takeoff 

from a high density altitude airport). One of the easiest ways to avoid 

it is to put the fuel pump near the fuel tank and pushing the fuel to 

the engine.



ashontz wrote:

 	  Quote: 	
		   

 

 Good to know, I'll probably install a return line myself. What can it hurt. I know all of my cars have a return line, probably for good reason too. Is the return line smaller?

 

 That being the case, I always hear the term vapor lock, in technical terms can someone explain EXACTLY what it is and where in the fuel system it occurs generally for everyone's benefit? I know sometimes my old lawnboy mower won't start after running for awhile and I need to take the air filter off to let it breath better so I can restart it. I assume this is vapor lock, but I'm not really sure. I've never had it stop running, but restarting was a major problem before I replaced the mower due to other problems with the mower being a yardsale total piece of crap I bought when I was poor years ago and not worth fiddling with everytime I wanted to mow the lawn.

 


	


-- 

Bryan Martin

Zenith 601XL N61BM

Ram Subaru, Stratus redrive

Do Not Archive

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

wjones(at)brazoriainet.co
Guest

Posted: Tue Dec 18, 2007 5:41 am Post subject: Is check valve in fuel return line needed?

Bryan ,what you say is very true .However you can have vapor lock when no 

fuel pump is used .I fly a Sonerai that has a gravity fuel delivery system 

.In the Texas heat along with 450 degree cylinder head temps I get vapor 

lock when using auto fuel .There  was no problems when using 100LL .Those 

high temps was when I had a VW engine ,I now have an 0200 Cont. and the CHT 

is around 360 degrees .

Wade Jones    South Texas

601XL plans building

Cont. 0200

---

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Tue Dec 18, 2007 6:48 am Post subject: Is check valve in fuel return line needed?

Yes, a vapor bubble in the line can block the flow of liquid fuel in 

some cases. An electric boost pump upstream of the area where the bubble 

forms can cure the problem.

wade jones wrote:

 	  Quote: 	
		   

 

 Bryan ,what you say is very true .However you can have vapor lock when 

 no fuel pump is used .I fly a Sonerai that has a gravity fuel delivery 

 system .In the Texas heat along with 450 degree cylinder head temps I 

 get vapor lock when using auto fuel .There  was no problems when using 

 100LL .Those high temps was when I had a VW engine ,I now have an 0200 

 Cont. and the CHT is around 360 degrees .

 Wade Jones    South Texas

 601XL plans building

 Cont. 0200


	




-- 

Bryan Martin

Zenith 601XL N61BM

Ram Subaru, Stratus redrive

Do Not Archive

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

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