Fuel Flow Discussion, Moved from Float Mounting

[Sir Newton]

Thank-you
I am reading the thread now. I would have missed this completely had you not moved it.

[Sir Newton]

yes, 100%
This stuff scares me during my pillow time!

[Sir Newton]

100% it's worth discussing. The loss of one plane is to many planes.

[Sir Newton]

Thanks for posting, this information Matt.

[Nev]

That's very interesting. I had also thought that it might act as a mini header tank, but in this case it wouldn't.

[jaredyates]

The gascolator doesn't deliver from the bottom, so it wouldn't need to be empty in order to deliver air. It would only need to lose enough fuel to unport the fittings.

[Nev]

Brooks mentioned earlier in this thread that he wondered if fuel could be flowing laterally through the fuel selector when in the BOTH position. I also got to wondering further about the whole "can a fuel pump suck air" issue. Previously I'd assumed it could. But I now have an issue with this - the fuel pump is flooded from the gascolator. The gascolator would have to empty first, before the pump could "suck" air.

In the BOTH position, at least one tank should be keeping the gascolator topped up.

Could a lateral fuel flow through the gascolator in the BOTH position create a Venturi like condition ? With a fuel pump "pulling" from the front, and a lower pressure at the back, could fuel vapor form? Could it even empty the gascolator back into the high tank ?

I realize that I'm going right off the reservation, but I'm not certain that the issue was ever resolved conclusively.

Some of you have a fluid dynamics or fuel system design background and can probably shed light on this for me.

[alaskabearhawk]

Same here. I checked my Newton SPRL valve and it doesn't crossfeed when in the OFF position.

[Battson]

I have one of the SPRL valves and it won't crossfeed in the off position.

[zkelley2]

Does this apply to any valve commonly used in the Bearhawk? Or are we having a trivia moment

I'll have to go back and look at some drawings to confirm, but I was under the impression that the SPRL valve most people use is that way.

[Nev]

Very good point.

[Battson]

Does this apply to any valve commonly used in the Bearhawk? Or are we having a trivia moment

[zkelley2]

Any reason not to turn the fuel off, instead of leaving one tank ported to the engine?

Before anyone comes up with the old anecdote of taking off with the fuel selector "off".... first - please try priming and starting a Bearhawk with the fuel selector "off"... then we can talk.

Like whee said, in a lot of fuel valves, off is just both with the outlet pointed backwards, which is in this scenario the same effect as both.

[whee]

Some fuel valves, such as the valves found in many Cessnas, connect the left and right tanks together in the off position. If your goal is to prevent fuel transfer it would be worth checking the function of the valve you installed in your airplane.

[Nev]

Any reason not to turn the fuel off, instead of leaving one tank ported to the engine?

No reason at all - that would work equally as well to prevent fuel transfer

I have previously tested the scenario of starting the engine with the fuel selector off - it won't even pressurize, let alone start. So I agree, for a fuel injected Bearhawk the risk should be mitigated. Also for a carbureted aircraft with the correct sized carb bowl.

However one day I'll be in a different aircraft, so I try to develop habits that hold good for that scenario too. This is partly from losing a relative many years ago in this exact situation.