Fuel Pump venting

[Daryl Lueck]

I'm down to my last hookup for the engine and I'm confused. I have a IO360 - 180hp with Bendix injection. The engine driven fuel pump has a vent hole with no info in the manual on venting to where. My a&p doing my inspections says to run a line out the cowling. He says that the vent line is incase the pump builds too much pressure. Would this be dumping fuel? Doesn't sound like I want to dump fuel out the cowling.... Is this a fuel injection only issue or do carb'd engines have the vent also?

 

I'd like to start the engine this weekend, but this could put a damper on the whole thing.... thanks.

[Marc Zeitlin]

Originally posted by Daryl Lueck

My a&p doing my inspections says to run a line out the cowling. He says that the vent line is incase the pump builds too much pressure. Would this be dumping fuel?

I don't know whether the pump is the same on the carbureted and injected version of the O-360, but I DO know that there's a vent on the carbureted one. I put a right angle tube fitting on it and ran a hose from there to the bottom cowling flange. I drilled a hole in the flange and siliconed the tube in place, with clearance in the bottom cowl flange to clear it.

 

It would, in fact, dump fuel overboard if the pump overpressures, but I've never actually heard of that happening, so it'll be pretty rare. Also, better OUT of the cowling than IN it.

[No4]

I quite often fly a Piper Arrow with a 200hp IO-360. If you have the electric fuel pump on and full fuel flow for too long (5 seconds) at start up, it will flood and a big pool of avgas appears behind the nose wheel. If that was trapped in a hot cowling I'd be moving the other way reasonably fast. They can flood badly, you have to be very careful starting those motors, go easy on the pump and mix, and give it plenty of throttle. Also they vapour lock if you try to restart when they are hot.

I'd also say to make sure the vent is nowhere near the exhaust pipe.

[s35pilot]

I vented the fuel pump on my cozy out the bottom at the lower flange. The purpose of this vent is in case the diaphram fails the raw gas will flow outside the aircraft not through the engine compartment and possibly creating a fire.

[Daryl Lueck]

Thanks everyone. It sounds like I will vent out the bottom of the cowling like everyone else. I did think about running it along side the exhaust, like the breather tube. Then if it vents I'd receive an afterburner effect from the fuel igniting. Would have looked pretty nice at night.

 

Thanks again.