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Date: Thu, 30 Jun 2011 19:10:15 -0400
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From: Colyn Case <colyncase@earthlink.net>
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Subject: fuel vent check valves more measurements - are they worth it?
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I've completed my marginally scientific tests on the Andair fuel check =
valves part number ck250E-B.
Summary:   bleed rate is too slow to balance the pressure in the tank by =
about 2:1 in a max rate climb.
If you fixed that the bleed function could still cut your spillage as =
the result of a taxi turn or a short taxi
across a slanted ramp by a factor of 78:1.   Of course it would have no =
effect on the result of leaving your
airplane parked in the sun or on a slanted ramp.

The introduction of the check valve does increase the risk of blockage =
in either direction.

Details.

Measurements

I measured the time to fully inflate a 5 quart baggy (by blowing into =
it)  and came up with these numbers.  I don't like the taste of gasoline =
so I used water instead of gas for the liquid tests.   I realize =
viscosity differences could significantly change these results.

bleed rate of air:  .82 cups/second.    =20

bleed rate of water:  .00159 cups/second

unrestricted flow rate of water: not less than .25 cups/second.

Climb pressurization problem=20

Then, suppose you climb at 2000 fpm to fl200 and one 51 gallon wing tank =
is empty.   That will take you 10 minutes.
The density of air is about half what it is on the ground so you will =
have to move a maximum of 51 gallons of air (albeit less dens air as you =
go). =20

time to bleed 51 gallons of air:  (51*16)/.82 =3D 995 seconds or 19.9 =
minutes.

best case climb time to fl200 =3D 10 minutes.

flow rate must be increased 2x to insure pressure inside the tank is =
always balanced to ambient.

Fixing it

You can increase the air bleed rate by drilling a couple more small =
holes in the bleeder side of the mechanism.

This will increase the liquid bleed rate.   I think this is a non-linear =
function but taking the worst case linear result, that would yield  =
.00318 cups/second liquid flow rate.

max water (standing in for fuel) that could be dumped in a 5 second turn =
=3D .0159  cups
unrestricted 1.25 cups

max fuel that could be dumped in a 20 second taxi =3D .0636 cups
unrestricted =3D 5 cups

Risk of blockage

The check valve mechanism has two extremely small (about 1mm)  holes in =
the bleed direction and 8 approximately 1/8" holes in the normal  flow =
direction.   The modification I envision would add two more 1mm holes in =
the bleed direction.   I think there is very little risk of blockage =
(beyond that of the vent tube itself) in the normal flow direction.   In =
the bleed direction, if your tank had a lot of granules on order 1mm in =
size, and they managed to find their way to the vent tube, and they all =
gathered on the bleed outlet at once, you could get blockage in the =
bleed direction.  However, that piece moves when the flow changes back =
to normal so that blockage of the bleed holes would not affect inward =
flow.

Conclusion

If you have these valves installed, you might want to consider =
modification or removal.
If you are considering modifying these valves and adding them to your =
vent system the tradeoff is as follows:
In exchange for adding a risk of blockage in the bleed direction you =
reduce taxi spillages from not much to nearly nothing.  Spillage due to =
fuel expansion or parking on a slanted ramp will be about the same with =
or without the valve installed.


--Apple-Mail-948-453276438
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<html><head></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; =
"><div>I've completed my marginally scientific tests on the Andair fuel =
check valves part number ck250E-B.</div><div>Summary: &nbsp; bleed rate =
is too slow to balance the pressure in the tank by about 2:1 in a max =
rate climb.</div><div>If you fixed that the bleed function could still =
cut your spillage as the result of a taxi turn or a short =
taxi</div><div>across a slanted ramp by a factor of 78:1. &nbsp; Of =
course it would have no effect on the result of leaving =
your</div><div>airplane parked in the sun or on a slanted =
ramp.</div><div><br></div><div>The introduction of the check valve does =
increase the risk of blockage in either =
direction.</div><div><br></div><div><b>Details.</b></div><div><br></div><d=
iv><b>Measurements</b></div><div><b><br></b></div>I measured the time to =
fully inflate a 5 quart baggy (by blowing into it) &nbsp;and came up =
with these numbers. &nbsp;I don't like the taste of gasoline so I used =
water instead of gas for the liquid tests. &nbsp; I realize viscosity =
differences could significantly change these =
results.<div><br></div><div>bleed rate of air: &nbsp;.82 cups/second. =
&nbsp; &nbsp;&nbsp;<div><br></div><div>bleed rate of water: &nbsp;.00159 =
cups/second</div><div><br></div><div>unrestricted flow rate of water: =
not less than .25 cups/second.</div><div><br></div><div><b>Climb =
pressurization problem&nbsp;</b></div><div><br></div><div>Then, suppose =
you climb at 2000 fpm to fl200 and one 51 gallon wing tank is empty. =
&nbsp; That will take you 10 minutes.</div><div>The density of air is =
about half what it is on the ground so you will have to move a maximum =
of 51 gallons of air (albeit less dens air as you go). =
&nbsp;</div><div><br></div><div>time to bleed 51 gallons of air: =
&nbsp;(51*16)/.82 =3D 995 seconds or 19.9 =
minutes.</div><div><br></div><div>best case climb time to fl200 =3D 10 =
minutes.</div><div><br></div><div>flow rate must be increased 2x to =
insure pressure inside the tank is always balanced to =
ambient.</div><div><br></div><div><b>Fixing =
it</b></div><div><b><br></b></div><div>You can increase the air bleed =
rate by drilling a couple more small holes in the bleeder side of the =
mechanism.</div><div><br></div><div>This will increase the liquid bleed =
rate. &nbsp; I think this is a non-linear function but taking the worst =
case linear result, that would yield&nbsp;&nbsp;.00318 cups/second =
liquid flow rate.</div><div><br></div><div>max water (standing in for =
fuel) that could be dumped in a 5 second turn =3D .0159 =
&nbsp;cups</div><div>unrestricted 1.25 cups</div><div><br></div><div>max =
fuel that could be dumped in a 20 second taxi =3D .0636 =
cups</div><div>unrestricted =3D 5 cups</div><div><br></div><div><b>Risk =
of blockage</b></div><div><b><br></b></div><div>The check valve =
mechanism has two extremely small (about 1mm) &nbsp;holes in the bleed =
direction and 8 approximately 1/8" holes in the normal &nbsp;flow =
direction. &nbsp; The modification I envision would add two more 1mm =
holes in the bleed direction. &nbsp; I think there is very little risk =
of blockage (beyond that of the vent tube itself) in the normal flow =
direction. &nbsp; In the bleed direction, if your tank had a lot of =
granules on order 1mm in size, and they managed to find their way to the =
vent tube, and they all gathered on the bleed outlet at once, you could =
get blockage in the bleed direction. &nbsp;However, that piece moves =
when the flow changes back to normal so that blockage of the bleed holes =
would not affect inward =
flow.</div><div><br></div><div><b>Conclusion</b></div><div><b><br></b></di=
v><div>If you have these valves installed, you might want to consider =
modification or removal.</div><div>If you are considering modifying =
these valves and adding them to your vent system the tradeoff is as =
follows:</div><div>In exchange for adding a risk of blockage in the =
bleed direction you reduce taxi spillages from not much to nearly =
nothing. &nbsp;Spillage due to fuel expansion or parking on a slanted =
ramp will be about the same with or without the valve =
installed.</div><div><br></div><div><br></div><div><br></div></div></body>=
</html>=

--Apple-Mail-948-453276438--