Low points in firewall-forward fuel lines

[Thermos]

A question for the group -

I'm making measurements for a firewall-forward fuel line order from TS Flightlines, for an IO-360-M1B on my RV-7. The most practical way to run the firewall-to-fuel pump line is to have it go down slightly to clear one of the engine mount cross-braces. Here's a pic of a test fit with a spare piece of 3/8" line from the engine kit..



I plan to have a 45 degree fitting on the firewall end, and a 90 degree fitting on the fuel pump end.

So my question is whether it's bad form to have a low point in a firewall-forward fuel line. I've heard and read advice that says there should always be drains at low points in the fuel system, but there are a lot of places in the RV-7/9 (like the hard lines between the tanks and fuel selectors) where there are low points with no drain.

Any thoughts from the experts?

Dave

[snopercod]

I would be uncomfortable with that loop hanging down like that. Is there no way you could route the line above the engine mount and straight into the fuel pump?

[Toobuilder]

Hard to tell from the picture, but it looks like the outlet at the firewall (if that's it at the zinc chromate doubler) should keep the straight fitting. The hose will exit straight forward under the mount and curve up to the pump. If there is enough offset, keep the fuel pump fitting straight and make the hose bend with two 90's. If the offset is too tight, keep the straight fitting at the pump but have Tom build you a hose with a bent 90 on one end (much like the picture shows). If there is any way to avoid a 90 AN fitting on the suction side, go that way.

[Thermos]

Originally Posted by Toobuilder

If there is enough offset, keep the fuel pump fitting straight and make the hose bend with two 90's. If the offset is too tight, keep the straight fitting at the pump but have Tom build you a hose with a bent 90 on one end (much like the picture shows). If there is any way to avoid a 90 AN fitting on the suction side, go that way.

Thanks Michael...that's what I was considering also. I definitely want to avoid an AN elbow fitting on the pump inlet, hopefully there are no fuel-flow disturbance issues with a 90 degree full-flow hose end.

Not sure, though, if a piece of fire-sleeved 3/8" hose can be bent tightly enough to go straight into the bulkhead fitting...?

Dave

[TS Flightlines]

Sorry I missed this---was taking a day off.
Stock supply hose is 14 inches, and clears the mount and can route to the pump with straight hose ends. Should also clear the governor.
Tom