Re: Fuel Vent Line

French <LJFrench@...>

Remember, what really matters - even with a float bowl carburator - is the difference in pressure between the carb bowl and the tank pressure. After all, all the vent pressure in the world coming from ram air will not do any good if the float bowl is seeing the same pressure. Same goes for the head pressure of the fuel supply above the carb. A header tank 10 feet above the carb doesn't help if the float bowl pressure overcomes the added head pressure. If you measure 100 GPH fuel flow from your fuel system on the ground at the carb, it doesn't mean in any way that you have a system capable of delivering any where near that amount of fuel flow in flight.

Anybody know what pressure is in the float bowl under various flight conditions (a clue is in the mixure control...anybody need the MA-3SPA handbook)???

Anybody know what pressure is being provided by the ram air vent under various flight conditions??

Woudn't it be awsome if there was some enhancement to the vent system of the plans Q200 that would avoid fuel starvation if you accidently flooded the vent system by overflowing the main tank from the auxillary tank, or if the gas cap accidently got a crack in it that didn't get detected, or any of the many other "accidents" that have happened with our systems. Now that would really be cool.......a root cause fix.

Lynn French

----- Original Message -----
From: "Jim Patillo" <logistics_engineering@...>
To: <Q-LIST@...>
Sent: Tuesday, August 08, 2006 12:03 PM
Subject: [Q-LIST] Re: Fuel Vent Line


it does
make some sense for the Posa carb without a fuel bowl. First hand
knowledge is critical.
How do
you account for all the hours we've flown without fuel starvation?
That is not by luck my friend.

My comments are directed at
new builders and how to make a simpler fuel fill and delivery system
that works.
----- Original Message -----
From: peterjfharris
To: Q-LIST@...
Cc: Jim Patillo
Sent: Tuesday, August 08, 2006 12:48 AM
Subject: Re: [Q-LIST] Re: Fuel Vent Line

The risk of fuel blown on the canopy from a header vent is zero
provided the vent is NOT fitted into the fuel return line. Mine is
fitted into the fuel return as per plans amendment and I have seen a
small splash of fuel on the canopy twice in the last 3 years. Also
it could be mounted clear of view.The point about this type of vent
is that it clears immediately under air pressure combined with
gravity. In the plans system gravity is working against air pressure
so fuel is held up frequently in the excessively long
pipe ,restricting flow to the carb fuel bowl and enough to stop a
Posa with no bowl. I am pleased I do not need to think about this
unnecesary restriction to fuel flow to my Jab.I would think twicw
before fitting a check valve in the return line as it is another
element that could fail.

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