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  #11  
Old 03-28-2016, 07:41 AM
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Saville Saville is offline
 
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Quote:
Originally Posted by Kevin Horton View Post
If you don't understand this, conduct a practical test - get some clear, flexible tubing and a T connector. Cut three lengths of tubing and put one piece on each leg of the T. Take two glasses with water - one mostly full, and one mostly empty. Put one piece of tubing in each glass, then suck on the third piece. Watch what happens when the first glass runs dry - suddenly you are sucking air, not water. Now, imagine that each glass is a fuel tank, and replace the water with fuel - your engine will stop once the first tank runs dry, no matter how much fuel is in the second tank.

A Both position works on a high wing aircraft because gravity will cause the tank with fuel to feed even if the other tank is empty. Both positions are bad, bad news on low wing aircraft, unless there is a header tank that is fed by gravity from both wing tanks.


No need - I understand it completely.
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  #12  
Old 03-28-2016, 11:35 AM
jdmunzell jdmunzell is offline
 
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.....nothing like one picture is worth a thousand words!
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  #13  
Old 03-28-2016, 11:43 AM
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Mike S Mike S is offline
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High wing, doesnt count.

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  #14  
Old 03-28-2016, 11:55 AM
rightrudder rightrudder is offline
 
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Yeah, sorta high wing, but I think the tubes come in from the top of the cups! (Not gravity feed)
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Last edited by rightrudder : 03-28-2016 at 12:22 PM.
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  #15  
Old 03-28-2016, 11:58 AM
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Saville Saville is offline
 
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Originally Posted by Mike S View Post
High wing, doesnt count.



Ok so the test procedure I understand best is the following:

1) First, check the tank vent inlets to be sure they are clear.

2) If I'm not alone, blow air into each vents and listen for bubbles coming out of the appropriate tank. This helps to assure the vent lines are connected and operative.

3) Disconnect the fuel line to the engine, on the engine side of the firewall

4) Attach a hose from that line to a bucket

5) Measure the fuel levels in the two tanks as accurately as possible.

6) Set the tank selector to OFF.

7) Turn aux fuel pump on....no fuel (or very little) should come out of the hose into the bucket.

Question: this is ok for the pump?

8) Set fuel selector to LEFT

9) Turn on pump, for a few seconds

10) Stop pump and measure both tanks.

11) Set fuel selector to RIGHT

12) Turn on pump for a few seconds; stop pump; measure tanks.

13) Set fuel selector on BOTH

14) Turn on pump for a few seconds; stop pump; measure tanks.


This series of steps will tell me if the system is working, and also will indicate how it is plumbed.

Do I have that right?

Anything wrong or unsafe?

Thanks
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  #16  
Old 03-28-2016, 12:11 PM
rightrudder rightrudder is offline
 
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That sounds like a good procedure. On question No. 7, you can run the pump dry, but not for an extended period.

The big takeaway is to either replace the valve with one that has Left, Right and Off positions, or use the existing valve and just never use the Both position. If it were me, I'd replace the valve so there is no possibility of error.
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  #17  
Old 03-28-2016, 12:13 PM
Chkaharyer99 Chkaharyer99 is offline
 
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#1 Ground the airframe.
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  #18  
Old 03-28-2016, 12:17 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Saville View Post


2) If I'm not alone, blow air into each vents and listen for bubbles coming out of the appropriate tank. This helps to assure the vent lines are connected and operative.
You can do it alone also....

With the cap removed, blow low pressure air into the vent inlet.
Because the fuel vapors are heavier than air it is easy to see teh vapor plume come out of the filler hole.

Running the pump for a few seconds with the fuel selector off shouldn't hurt it. It will only take a couple seconds to confirm it is not pumping fuel. Don't leave it on for an extended time.

The rest of your test plan looks good.
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  #19  
Old 03-28-2016, 12:21 PM
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Saville Saville is offline
 
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Quote:
Originally Posted by Chkaharyer99 View Post
#1 Ground the airframe.
Yep. Should have written that first.
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  #20  
Old 03-28-2016, 12:21 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
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Quote:
Originally Posted by Saville View Post



Ok so the test procedure I understand best is the following:

1) First, check the tank vent inlets to be sure they are clear.

2) If I'm not alone, blow air into each vents and listen for bubbles coming out of the appropriate tank. This helps to assure the vent lines are connected and operative.

3) Disconnect the fuel line to the engine, on the engine side of the firewall

4) Attach a hose from that line to a bucket

5) Measure the fuel levels in the two tanks as accurately as possible.

6) Set the tank selector to OFF.

7) Turn aux fuel pump on....no fuel (or very little) should come out of the hose into the bucket.

Question: this is ok for the pump?

8) Set fuel selector to LEFT

9) Turn on pump, for a few seconds

10) Stop pump and measure both tanks.

11) Set fuel selector to RIGHT

12) Turn on pump for a few seconds; stop pump; measure tanks.

13) Set fuel selector on BOTH

14) Turn on pump for a few seconds; stop pump; measure tanks.


This series of steps will tell me if the system is working, and also will indicate how it is plumbed.

Do I have that right?

Anything wrong or unsafe?

Thanks
Safety,
For a recent fuel test we grounded the airframe to the discharged fuel with a bare wire dropped into the fuel container. Ground and un ground it at the clip end, not by dropping in the container.

Testing You are on a good path here. Place the tail up so the plane is level. At that attitude the fuel will siphon out when you remove the hose at the fuel pump, so turn the valve to "off"

Testing with the boost pump to determine the valve function is good. A gravity flow test to verify flow with and w/o fuel cap on can check the vents once you are sure what the valve does.

To measure fuel drop in a tank might be tricky, even at 35 gph, a minute is 1/2 gal, how much is that on a dip stick? Think about that one.

Vent test - do that first, as a boost pump could draw significant negative pressure and be bad for the skin. Or just leave the caps loose for the test.

Have fun learning!
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and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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