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Fuel Return Tee

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pbesing(at)yahoo.com
Guest

Posted: Tue May 09, 2006 7:33 pm Post subject: Fuel Return Tee

I'm plumbing in a new fuel selector, and instead of

having my fuel return (older simmons injection that

has a fuel return) return to the tank, was thinking of

plumbing in a tee in the line just before the fuel

pump. This is because the fuel return is currently

going to one tank, and makes fuel management a chore. 



Any reason why I shouldn't do this? Cavatation, etc?



Paul Besing

__________________________________________________

Bruce(at)glasair.org
Guest

Posted: Tue May 09, 2006 8:06 pm Post subject: Fuel Return Tee

Andair has a more elegant solution, a double valve fuel selector. It

switches the return line to the tank from which you are drawing.



Bruce

www.glasair.org

 



--

Albert Gardner

Joined: 10 Jan 2006
Posts: 455
Location: Yuma, AZ

Posted: Tue May 09, 2006 8:15 pm Post subject: Fuel Return Tee

This is the method that's being used in the RV-10. The fuel is returned to a

T installed in the line between the fuel selector valve and the fuel filter.

Albert Gardner

RV-10 #422



--

_________________
RV-9A N872RV
RV-10 N991RV

jmpcrftr(at)teleport.com
Guest

Posted: Tue May 09, 2006 8:15 pm Post subject: Fuel Return Tee

Vapor Lock

Assuming this is a continuous full time re-circulation.  Fuel gets 

heated as it circulates through the fuel injection components up 

front.  It needs to go to the tank to cool.  It can get hot enough 

that the boost pump doesn't create enough pressure to overcome the 

vaporization.



I'm not familiar with the Simmons injection you mentioned.  This is a 

typical question/problem for alternate engine installations.  These 

typically have a constant volume or high pressure pump that has a 

high recirc volume through the pressure regulator.  In this case we 

have to use something like the Andair Duplex (six port) fuel valve so 

the recirc goes to the tank it came out of.  This valve eliminates 

the fuel management issue you talked about.  The valve is 

unfortunately very expensive at over 

$300.  http://www.andair.co.uk/system/index.html



Mike

Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR

13B in gestation mode, RD-1C, EC-2

At 20:31 2006-05-09, you wrote:

 	  Quote: 	
		  



I'm plumbing in a new fuel selector, and instead of

having my fuel return (older simmons injection that

has a fuel return) return to the tank, was thinking of

plumbing in a tee in the line just before the fuel

pump. This is because the fuel return is currently

going to one tank, and makes fuel management a chore.



Any reason why I shouldn't do this? Cavatation, etc?



Paul Besing

pbesing(at)yahoo.com
Guest

Posted: Tue May 09, 2006 8:32 pm Post subject: Fuel Return Tee

Yeah, I saw that, very pricey, and I only have one

line plumbed to one tank.  I'd have to spend the $400

on the selector, remove the right tank, take the

sender bracket off, plumb a return line to the tank,

etc, etc.  I thought it was much easier just to plumb

the return back into the system, instead of the tank

it comes from.



Paul Besing



--- Bruce Gray <Bruce(at)glasair.org> wrote:



[quote] 

 <Bruce(at)glasair.org>

 

 Andair has a more elegant solution, a double valve

 fuel selector. It

 switches the return line to the tank from which you

 are drawing.

 

 Bruce

 www.glasair.org

  

 

 --

Albert Gardner

Joined: 10 Jan 2006
Posts: 455
Location: Yuma, AZ

Posted: Tue May 09, 2006 8:46 pm Post subject: Fuel Return Tee

I think this will link to a picture of the assembly out of the plane.

Builder is Larry Rosen.

http://lrosen.nerv10.com/Construct/Log/Fuselage/Fuel_lines/slides/2006-02-27

-fuel-27.html

Albert Gardner

RV-10 #422

_________________
RV-9A N872RV
RV-10 N991RV

pbesing(at)yahoo.com
Guest

Posted: Tue May 09, 2006 9:38 pm Post subject: Fuel Return Tee

It's only about 1 GPH that returns..wouldn't 1 GPH

mixing with 9 GPH cool enough?



--- Michael McGee <jmpcrftr(at)teleport.com> wrote:



 	  Quote: 	
		   

 <jmpcrftr(at)teleport.com>

 

 Vapor Lock

 Assuming this is a continuous full time

 re-circulation.  Fuel gets 

 heated as it circulates through the fuel injection

 components up 

 front.  It needs to go to the tank to cool.  It can

 get hot enough 

 that the boost pump doesn't create enough pressure

 to overcome the 

 vaporization.

 

 I'm not familiar with the Simmons injection you

 mentioned.  This is a 

 typical question/problem for alternate engine

 installations.  These 

 typically have a constant volume or high pressure

 pump that has a 

 high recirc volume through the pressure regulator. 

 In this case we 

 have to use something like the Andair Duplex (six

 port) fuel valve so 

 the recirc goes to the tank it came out of.  This

 valve eliminates 

 the fuel management issue you talked about.  The

 valve is 

 unfortunately very expensive at over 

 $300.  http://www.andair.co.uk/system/index.html

 

 Mike

 Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR

 13B in gestation mode, RD-1C, EC-2

 

 

 At 20:31 2006-05-09, you wrote:

 >

 <pbesing(at)yahoo.com>

 >

 >I'm plumbing in a new fuel selector, and instead of

 >having my fuel return (older simmons injection that

 >has a fuel return) return to the tank, was thinking

 of

 >plumbing in a tee in the line just before the fuel

 >pump. This is because the fuel return is currently

 >going to one tank, and makes fuel management a

 chore.

 >

 >Any reason why I shouldn't do this? Cavatation,

 etc?

 >

 >Paul Besing

 

 

 

 

 



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__________________________________________________

retasker(at)optonline.net
Guest

Posted: Tue May 09, 2006 10:17 pm Post subject: Fuel Return Tee

Yes, but depending on how much fuel is consumed on each trip around the 

circuit the fuel may get very hot and then you have the makings of a 

vapor lock problem.  If you don't want to replumb it to return fuel back 

to the source tank, any chance you can add a small header tank?  That 

would allow more volume of fuel to dissipate any heat from the pass 

through the fuel circuit.

On the other hand, if a significant portion of the pumped fuel is 

consumed each time around the circuit, it may be no problem at all.

My $0.02.  I have one of the $300 Andair fuel valves   .

Dick Tasker

Paul Besing wrote:

[quote]

Yeah, I saw that, very pricey, and I only have one

line plumbed to one tank.  I'd have to spend the $400

on the selector, remove the right tank, take the

sender bracket off, plumb a return line to the tank,

etc, etc.  I thought it was much easier just to plumb

the return back into the system, instead of the tank

it comes from.

Paul Besing

--- Bruce Gray <Bruce(at)glasair.org> wrote:

>

><Bruce(at)glasair.org>

>

>Andair has a more elegant solution, a double valve

>fuel selector. It

>switches the return line to the tank from which you

>are drawing.

>

>Bruce

>www.glasair.org

> 

>

>--

Bruce(at)glasair.org
Guest

Posted: Tue May 09, 2006 11:16 pm Post subject: Fuel Return Tee

The most critical time for vapor lock is after you rotate on takeoff after a

long time at idle power. There's only 2 ways to reduce the possibility of

vapor lock, decrease the temperature of the fuel or raise the pressure in

the fuel line. We also have to consider the different locations where vapor

lock can occur. The most common is the low/suction side of the engine driven

fuel pump. If the fuel or pump temperature is at it's vapor point, the

pressure drop at the fuel pump will vaporize it and no more pumping. That's

the condition the electric fuel pump is likely to correct. The next most

likely is the fuel servo, this is already seeing the high pressure of the

engine pump, so turning on the electric pump is not likely to have much

beneficial effect. Your best choice here is, a thermal brake between your

servo and the engine induction housing (fiberglass/wood gasket/spacer) or

cooling the servo case with fuel flow. This condition is what the fuel

return line is designed to cure. If the engine is already at full power the

extra 1 gph of a return line will have little effect. So the return line can

only be beneficial from a preventative standpoint. It's designed to cool the

servo during long taxi periods at idle power. There might be some benefit to

running the engine at mid power levels after a long taxi before takeoff on

hot days for 3-5 minutes to cool the servo with fuel if you don't have a

return line.



Vapor lock in the feed line from the servo to the spider is only an issue

for hot starts. Some FI systems have a purge line on the distribution spider

to solve this issue. 



One other area of concern is that our diaphragm type of engine fuel pumps

have a failure mode that will block the fuel line and not allow fuel to

reach the servo even with the electric pump operational. Some builders have

installed a second faucet type pump with check valve and plumbed to a T

right at the main inlet of the fuel servo. This pump is always left on. Gear

driven fuel pumps (Lear-Romec) don't have this failure mode



Bruce

www.glasair.org

rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Tue May 09, 2006 11:20 pm Post subject: Fuel Return Tee

 	  Quote: 	
		   I'm plumbing in a new fuel selector, and instead of

 having my fuel return (older simmons injection that

 has a fuel return) return to the tank, was thinking of

 plumbing in a tee in the line just before the fuel

 pump. This is because the fuel return is currently

 going to one tank, and makes fuel management a chore. 

 

 Any reason why I shouldn't do this? Cavatation, etc?


	


Paul,



Clearly the best way is the Andair valve that directs

the return to the same tank as the source.  If that's

off the table, I would just make sure that after you

fill up, you select the tank that has the return line.

After burning a few gallons, then you should be ok to

switch tanks, keeping in mind the tank without the

return will empty a bit more quickly.



I would not return the hot, possibly vapor laden fuel

to the intake of the fuel pump, since as you suggested,

cavitation and then vapor lock can happen.



I've read somewhere that fuel issues are one of the

leading cause of accidents in the first 10 hours of

flight in experimental aircraft, so this is an area

where I feel it is worth a lot of extra effort to

make it bulletproof.  I know that fuel delivery on

my Subaru powered RV8 has been the single largest

time sink for me.



-- 

Mickey Coggins

http://www.rv8.ch/

#82007 finishing

_________________
Mickey Coggins
http://www.rv8.ch/

pitts_pilot(at)bellsouth.
Guest

Posted: Wed May 10, 2006 6:01 am Post subject: Fuel Return Tee

Since we're talking servo's here, then we should only discuss the 

problem with fuel injection with this thread.

Bruce Gray wrote:



 	  Quote: 	
		  



The most critical time for vapor lock is after you rotate on takeoff after a

long time at idle power.



Why do you think this is so??  If you suffer vaopr lock at rotation, you 
	


would just roll out .... unless you're just cutting the runway length a 

little close!!! 



 	  Quote: 	
		   There's only 2 ways to reduce the possibility of

vapor lock, decrease the temperature of the fuel or raise the pressure in

the fuel line.



Agreed!
	




 	  Quote: 	
		   We also have to consider the different locations where vapor

lock can occur. The most common is the low/suction side of the engine driven

fuel pump. If the fuel or pump temperature is at it's vapor point, the

pressure drop at the fuel pump will vaporize it and no more pumping. That's

the condition the electric fuel pump is likely to correct. The next most

likely is the fuel servo, this is already seeing the high pressure of the

engine pump, so turning on the electric pump is not likely to have much

beneficial effect.



I kinda disagree .... If you plumb the pumps in parallel, then I agree. 
	


 But I don't know why you'd do that.  If plumbed in series, depending on 

the head pressure and temperature at the electric pump, you still may 

have a risk.  If you plumb the electric pump so it's low and inside the 

cockpit, you've pretty much conquered the vapor lock possibility.



 	  Quote: 	
		   Your best choice here is, a thermal brake between your

servo and the engine induction housing (fiberglass/wood gasket/spacer) or

cooling the servo case with fuel flow. This condition is what the fuel

return line is designed to cure. If the engine is already at full power the

extra 1 gph of a return line will have little effect.




	


But experiencing vapor lock usually precludes starting the engine. 

 Here's the rub.  You can use the electric pump to overcome the vapor 

problem and get cool fuel into the engine compartment ..... but you also 

risk the possibility of flooding.



 	  Quote: 	
		   So the return line can

only be beneficial from a preventative standpoint. It's designed to cool the

servo during long taxi periods at idle power.



Not true.  It's designed to return excess fuel to the tank instead of 
	


creating an excessively rich condition.  Not all fuel servo's have a 

return line.



 	  Quote: 	
		   There might be some benefit to

running the engine at mid power levels after a long taxi before takeoff on

hot days for 3-5 minutes to cool the servo with fuel if you don't have a

return line.



I doubt it.  If the engine is running, then the system is supplied with 
	


cooler fuel already and the servo is under pressure ..... hence no vapor 

problem.



 	  Quote: 	
		  Vapor lock in the feed line from the servo to the spider is only an issue

for hot starts. Some FI systems have a purge line on the distribution spider

to solve this issue. 



OK.
	




 	  Quote: 	
		  One other area of concern is that our diaphragm type of engine fuel pumps

have a failure mode that will block the fuel line and not allow fuel to

reach the servo even with the electric pump operational.



You'll have to tell me what that is.  Pressure on the inlet to the 
	


mechanical pump will flow through the two reed valves with no problem.



 	  Quote: 	
		   Some builders have

installed a second faucet type pump with check valve and plumbed to a T

right at the main inlet of the fuel servo. This pump is always left on. Gear

driven fuel pumps (Lear-Romec) don't have this failure mode



Please tell me what that failure mode is.  AFAIK, what you describe is a 
	


reaction to a non-existent problem.

Linn

do not archive



 	  Quote: 	
		  Bruce

www.glasair.org

pitts_pilot(at)bellsouth.
Guest

Posted: Wed May 10, 2006 6:08 am Post subject: Fuel Return Tee

Mickey Coggins wrote:

 	  Quote: 	

>I'm plumbing in a new fuel selector, and instead of

>having my fuel return (older simmons injection that

>has a fuel return) return to the tank, was thinking of

>plumbing in a tee in the line just before the fuel

>pump. This is because the fuel return is currently

>going to one tank, and makes fuel management a chore. 

>

>Any reason why I shouldn't do this? Cavatation, etc?

>    

>

Paul,

Clearly the best way is the Andair valve that directs

the return to the same tank as the source.

Maybe not the best way INMHO, but a good idea.

 	  Quote: 	
		    If that's

off the table, I would just make sure that after you

fill up, you select the tank that has the return line.

After burning a few gallons, then you should be ok to

switch tanks, keeping in mind the tank without the

return will empty a bit more quickly.

That's not a good idea.  If you start with full tanks and (because 

you're human) don't have the selector on the 'return' tank, you'll just 

pump the return fuel overboard.

 	  Quote: 	
		  I would not return the hot, possibly vapor laden fuel

to the intake of the fuel pump, since as you suggested,

cavitation and then vapor lock can happen.

If you have fuel flow, then there's no vapor lock problem to begin with. 

 In a closed loop system where the hot fuel is returned to the input 

side of the mechanical pump, it's being mixed with cool fuel from the 

tank, so vapor lock shouldn't be an issue at that point.

 	  Quote: 	
		  I've read somewhere that fuel issues are one of the

leading cause of accidents in the first 10 hours of

flight in experimental aircraft, so this is an area

where I feel it is worth a lot of extra effort to

make it bulletproof.  I know that fuel delivery on

my Subaru powered RV8 has been the single largest

time sink for me.

I suspect that the issues you're referring to are caused by trash in the 

system from construction or deterioration of materials used in hte 

system.  Then comes issues relating to pickup of the fuel in the tank, 

fittings that aren't tight, and other assembly errors.  At the bottom of 

my list would be the yo-yo that doesn't fill it up!

Linn

do not archive

dan.beadle(at)inclinesoft
Guest

Posted: Wed May 10, 2006 6:45 am Post subject: Fuel Return Tee

I checked prices - these are over $500.  Very nice.  Seems like the best

solution.  



Recirculating warm fuel thru a T doesn't seem like a great solution for

cooling servo to get a Hot Start to work.  On my C414, they are very

difficult to start on a warm Nevada day after shutting down for 15-60

minutes.  Exchanging warm fuel from the servo for "cold" fuel from the tanks

seems the way to go.



Looking at the specs for the Andair valve, it says it is suitable for 200HP

engines.  They don't have a flow rate spec'ed.  I am going with a 210.  Is

there enough margin there?  What size fuel lines are you guys using for

IO390s?



Thanks



Dan Beadle

--

rvbuilder(at)sausen.net
Guest

Posted: Wed May 10, 2006 2:22 pm Post subject: Fuel Return Tee

Actually, there is a big difference between recirculating the fuel =

from the engine and what the whole Airflow Performance boost pump setup =

does.  The AP boost pump setup is full of check valves and bypasses that =

are mainly to protect the pump and make sure there is always fuel going =

to the engine.  It does not recirculate anything from the fuel injection =

servo.



Michael Sausen

RV-10 #352 Working on Fuselage

Do Not Archive

--

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