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Advice for gascolator quick drains

 
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dan(at)syz.com
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PostPosted: Wed Feb 14, 2018 6:55 pm    Post subject: Advice for gascolator quick drains Reply with quote

Hi everyone.

I have gascolators located in the wing roots of my RV-10 (here in Canada, we require them, whether they make logical sense or not).

They're at the lowest point in the fuel system I can get them (also required), though the true lowest point in the fuel system is the drains in the bottom of the tanks, since fuel has to flow uphill to get into the gascolator (from either direction). So I don't expect there to be much water ever get trapped in the gascolator. And in reality, though I had a bit of water I drained once from the bottom of the tanks (the result of a not-perfectly-sealed fuel cap when the plane was left outside in the rain once), I've never seen any in the gascolators. Nonetheless, I should have a quick drain, if for no other reason than to be able to check them periodically - though water won't naturally flow into them when the plane is at rest, when the fuel is flowing, I imagine small droplets in suspension with the fuel may get trapped in the bowl and slowly build up.

The trouble is that these gascolators aren't under positive pressure as gascolators would normally be - they'd be under a slight negative pressure as fuel is sucked from the tanks. I worry that if I used just a standard quick drain there might be the possibility of air leaking into the fuel line (I've seen those quick drains leak fuel on more than one occasion when the seal starts to degrade a bit - they seem to be notorious for that - so I'm reasonably certain they'd just as happily leak air in as well if they're under suction as they are). And I'm not too sure that having air bubbles in the fuel is altogether preferable to water droplets.

Does anyone have any good suggestions on how to handle this? I definitely don't expect to have to check for water after every flight as most would be drained from the tank drains anyway. Screwing in just a simple plug works reliably enough to keep the air out, but is a bit problematic to periodically check and drain (fuel tends to get everywhere when you try to thread the plug back into place). Is there a quick-drain suited for this sort of specific purpose? I'm thinking of maybe something that screws in to have a positive seal to prevent leakage, but unscrews slightly to let a bit of fuel drain out? Something better than just a spring pushing against an O-ring, or having a plug that has to be completely removed, in any event.

Thanks for any help or advice you might have!

Dan
---
Dan Charrois
President, Syzygy Research & Technology
Phone: 780-961-2213


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kearney



Joined: 20 Sep 2008
Posts: 544

PostPosted: Wed Feb 14, 2018 7:35 pm    Post subject: Re: Advice for gascolator quick drains Reply with quote

Dan

I would use solid bungs with thread sealant. When I had gascolators located in the wing roots I was very concerned about getting air into the fuel system.

I would not use quick drains.

Cheers

Les

PS: MDRA no longer "requires" gascolators provided functionality is met. Perhaps you could remove yours arguing that they are no longer required.


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