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Should I put a Fuel Drain Here?

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wsimpso1

Super Moderator
Staff member
Joined
Oct 18, 2003
Messages
11,357
Location
Saline Michigan
I thought that I had my fuel system resolved and going together, and then I came across something. Dave Prizio's book cautions us to ALWAYS put a fuel drain point at the lowest spot in out system... Well, I need a couple more hours at a buddy's mill to finish them, but things are getting crowded down there. Let's look at the system in the attached photo.

Wing tanks are in the outer panels of my wings, they have quick drain points at the very lowest spots in the tanks, and a pickup above the quick drain point.

The fuel line from each wing follows the lower wing skin then the fuselage belly skin, then near centerline up to a duplex selector valve and a pair of Facet 40109 pumps in parallel.

One of the Facet pumps is powered all of the time, and they run 32 gph.

The Facet pump moves fuel into a 10 gallon header tank that has a sump of 18 fluid ounces with a drain point below and a pickup above. The header tank overflows back to the selected tank via the duplex selector valve. So, when the header tank fills, it overflows to the wing selected and fuel circulates. And fuel keeps flowing at 32 gph from the tank selected to the header tank.

The low spot is near center line on the way from wing tank to selector valve. There is no sump here, just 3/8 x 035 aluminum tube. 32 gph in a 3/8 x 0.035 aluminum tube is about 28 in/sec. The entire line from wing tank to the header tank is 100" long, and 7 cubic inches of fuel. The portion that is below the wing tank is 55" long and less than 4 cubic inches - less than 2 fluid ounces. That line containing my low spot will be completely flushed to the header tank every four seconds during operation and I can sequester 18 fluid ounces of water there before the pickup will get much of it. It seems like a real stretch that the fuel line needs a drain between the wing and header tank to me...

So, let's hear if the cognoscenti feel I can skip these drains on the low spot, or if difficult package or not, it still needs to find a spot in my tight package here.

Billski
 

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