Eric,
Assuming all kinds of things and using pipe flow calculator for a gas known
as air:
If your engine is using 15 gal/hr = 2 cu ft/hr = .0335 cfm
Suppose the inside diameter of 1/4" tubing is .156", the pressure of the
air at the vent is .7 psi (about 200 kts) and the temp is 31F, then the air is
traveling in the tube at 3 Kts.
"So What?" You might ask.
OK then, take a gallon jug, fit a 3/8 inch tube (engine pump fuel line
size?) at one end and a quarter inch tube at the other end (vent
line). Use a good sealing putty. Fill the jug with water.
Let the water drain out the 3/8 tube and time it. If it drains in 3
minutes or less (1 gal/4 min = 15 gals/hr., 1 gal/3 min = 20 gph), the vent is
large enough. That's just using gravity - without assistance
from the engine pump or the vent pressure and 100LL may be less
viscous.
Grayhawk
PS Let us in on the results.
In a message dated 11/24/2008 10:01:34 P.M. Central Standard Time,
cassutt@windstream.net writes:
I am not
using the header tank in my 360 and have installed 1/4" od tubing as the vent
for each wing tank. My old SB manual says nothing about fuel vent size even
with the header and what published updates there are for the extended bay
don't have a size listed either. Is this big enough dia. for pulling
fuel straight from the wings or should it be larger? What have others
done.
Eric Demaray
360 SB
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