fuel tank vent

[Bacon8tor]

The check valve looks fascinating but I'm trying to figure out how it functions. It looks like it allows airflow INTO the tank to relieve the vacuum as fuel is consumed. But is it closing off the air and/or fuel from escaping the tank? If that's the case it is no longer "vented." I would think that would put a whole lot of stress on the tank as the fuel expands while being heated with nowhere to go especially if you topped off your tank and let it sit a few days in a warm climate. Maybe it works better in a cold climate with less expansion.

[peter anson]

The check valve has to be mounted vertically. I'm not familiar with the Onex tank but on the Sonex the vent is at the top and it's hard to imagine any other arrangement. In normal operation the vent allows air both in and out of the tank. The teflon ball is light enough so that if fuel sloshes up the vent it pushes the ball against the seat blocking it, only temporarily of course, but that's all you need; fuel sloshes are short duration. If the aircraft is inverted through either negative G or accident, the ball falls into the seat blocking it. There are dozens of versions of this sort of thing available for off road cars, usually intended as a safety device in case the car is rolled but they usually use a steel ball. I tried that on my Sonex but the steel ball was too heavy. It would only block the fuel if I did a fairly violent negative G maneuver. The lighter teflon ball is the key. I have had one of these fitted to my Sonex for about 4 years. It works perfectly.

Peter
Sonex 894

[Bacon8tor]

Okay. So I'm starting to get it. The ball vent DOES allow air to vent both ways. But what about fuel? Let's say the tank is topped of and for arguments sake there is no air in the tank. Will the ball prevent fuel from venting as it naturally expands from warming?

[NWade]

Okay. So I'm starting to get it. The ball vent DOES allow air to vent both ways. But what about fuel? Let's say the tank is topped of and for arguments sake there is no air in the tank. Will the ball prevent fuel from venting as it naturally expands from warming?

The fuel will not expand that much before it begins evaporating, and the vapors easily exit past the ball. Think about it for a minute: how many water bottles have ever exploded because they were put in the sun and left to warm up? Liquids do not change volume with temperature like gasses do.

Seriously, there are dozens of us Sonex owners who have Peter Anson’s vent; no one has had a problem with them that I’m aware of - they work great! Feel free to search the forums and check out his past posts and the threads by builders talking about his items.

—Noel
Sonex #1339

[peter anson]

Okay. So I'm starting to get it. The ball vent DOES allow air to vent both ways. But what about fuel? Let's say the tank is topped of and for arguments sake there is no air in the tank. Will the ball prevent fuel from venting as it naturally expands from warming?

If you fill the tank to the brim and then leave the aircraft parked in the sun on a hot day, the check valve won't prevent leakage. It won't stop a very slow flow rate caused by expansion of fuel. This has caused me problems exactly zero times.

Peter

[dbdevkc]

The fuel will not expand that much before it begins evaporating, and the vapors easily exit past the ball. Think about it for a minute: how many water bottles have ever exploded because they were put in the sun and left to warm up? Liquids do not change volume with temperature like gasses do.

Yep. Fill up a little plastic gas can, put the cap on the spout and set it in the hot sun. It builds up vapor gas pressure (it can be a lot if you have a air tight cap. Loosen the cap, and the vapor gas escapes - no noticeable expansion of the liquid fuel.

[Rofomoto]

Where is the valve installed at in regards to the ram air vent tube? Billy

[DCASonex]

Peter, Thanks for the clarification on the use of a Teflon ball, that now looks like a very sensible and practical devise.

David A.

[N190YX]

I am a little disturbed about reading in this thread the notion that liquid gasoline does not expand much when its temperature increases, I once filled the tank of a car in the morning, drove it home, and later in the hot afternoon liquid gasoline was dripping from the fuel filler cap down the side of the car into a pool of gas on the concrete driveway (years ago before cars had expansion room in the tanks). The volume of liquid gas does increase with temperature! I suggest you do not ignore this fact when designing the venting of your fuel system, so as not to have a fire hazard when the volume of liquid gas in a full tank does increase with increasing temperatures.

[dbdevkc]

I stand corrected. Fuel will expand with heat. MoGas will expand 2% when going from 60° to 90°.