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Subject: Re: [FlyRotary] Fuel Delivery - Vapor Lock Date: Thu, 17 Jun 2004 1:03:52 -0400 MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="----=____1087448632813_,oOROwv'y2" Message-Id: <20040617050353.VOGJ13993.fed1rmmtao11.cox.net@smtp.west.cox.net> This is a multi-part message in MIME format. ------=____1087448632813_,oOROwv'y2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Russell Duffy <13brv3@bellsouth.net> wrote: > At first glance, it would seem dangerous to have high pressure fuel in the > cockpit, but not when you think about it. First, it's extremely unlikely > that a line is just going to blow apart (I don't use automotive rubber lines > anywhere). If there's a leak, it's going to start small, and you'll smell > it when it's still just a tiny leak. If this were on the hot side of the > firewall, it would have to be a big leak before you smell it, and a fire > might actually be your first sign of trouble. Even if you had a big leak in > the cockpit, what's going to start the fire? You can have all the gas you > want, as long as you don't light it with something. What's going to start a fire? How about relay contacts opening? Keying a mic? There are lots of tiny little electrical events, any of which that could start a fire in a fuel-rich environment. Dale R. ------=____1087448632813_,oOROwv'y2 Content-Type: text/html; name="reply" Content-Disposition: inline; filename="reply" Message

Now, the Subie guys are contemplating a re-design of their fuel systems. I'm wondering now if I should make any changes to my fuel system (2 wing tanks, 6-port Andair valve, dual EFI pumps mounted on f/w)? Comments would be welcome, especially from those that have been flying for a while.

Mark S.

Hi Mark,

We're basically copying the fuel system that's used on the cars, and you just can't go wrong with the basic design. Where we get into trouble is when we make changes, even though we may not realize it.

After reading your message, the primary thing that sticks in my mind is- keep your pump and lines relatively cool. I think a little common sense goes a long ways here. In a car, the pump is usually in the tank, or very close to the tank, so it's effectively at OAT. There's a long line between it and the engine compartment, so even if you boil fuel in the engine compartment, the pump is still submerged, and will blow the air right through the regulator and back to the tank. As long as you don't do something silly like run the fuel lines next to the exhaust, the only time you should have a problem with fuel boiling is after shutdown.

I have to admit that I'm not personally comfortable with having the EFI pumps on the hot side of the firewall, unless you build a box around them, and supply lots of cool air. I have mine in the cockpit, along with the filters, and regulator. The only thing in the engine compartment is the lines that absolutely have to be there.

At first glance, it would seem dangerous to have high pressure fuel in the cockpit, but not when you think about it. First, it's extremely unlikely that a line is just going to blow apart (I don't use automotive rubber lines anywhere). If there's a leak, it's going to start small, and you'll smell it when it's still just a tiny leak. If this were on the hot side of the firewall, it would have to be a big leak before you smell it, and a fire might actually be your first sign of trouble. Even if you had a big leak in the cockpit, what's going to start the fire? You can have all the gas you want, as long as you don't light it with something.

The pumps, filters, and regulator are all cool, so the heated fuel is minimized. I run both EFI pumps in flight, so there's a ton of flow as well. In this configuration, there's absolutely no chance of vapor lock.

I realize that opinions vary on fuel systems, so take the above comments for what they're worth.

Cheers,

Rusty

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