PA30 Fuel Vents

[Frank Brunot]

While on a flight yesterday, I had one (not sure which) engine give a momentary "pause", then immediately return to normal. Thinking it over, it sounded like either momentary fuel starvation, or intake air blockage. The engine monitors showed no unusual signs. And fuels tanks had been drained that morning. All tanks full (90 gallons). I don't remember which tanks I was using at the time.

So being fairly new to FLA, I went out to the hanger today to check the fuel vents, to see if some friendly bugs were building a new home. So a couple of questions:

1) Can anyone suggest some kind of a rubber cone that I can attach a small hose to, so that I can blow into the vents. With the NACA vents, I can't figure out how to seal a tube in the vent.

2) Using a large (11") tie wrap, I probed the vents, and all seemed open except the Left Aux tank. The wrap hit something about 2-3" in, and wouldn't let it pass. I didn't try a piece of safety wire, for fear of poking a hole in something rubber. I did try a small screw driver, rotating it to see if I could loosen the blockage. Only got a tiny piece of aluminum. I see from the Parts books that the Aux tank vents have a weld about 2-3" in. Guessing that's what I hit.

3) While the Inboard (Main) tanks have a vent and drain (overflow?) tubes coming out, the Aux (Outboard) tanks have an extra tube coming out of the wings. What is it? It's not shown in the parts or maintenance manuals.

Thanks.

[N3322G]

Frank,

Sounds like you are may be of a mechanic than I am but one of the things to watch for on Twins are the alternate air doors and their operation. They are not the most robust of assemblies and they do wear and get out of adjustment and could account for the moment you mentioned. Easy to check on with maint man. guidance and a mirror and the outboard cheek cowl off. Webco has a whole bunch of the replacement parts - just had the Twin's worked on again this annual.

wrt clearing vent lines, you'll need help from someone else. Clifton Aero take care of my Twin in that regard ... although if I were going to try to clear a line away from home, I might try flexible tubing of a smaller diameter than the hose/vent. No guarantee it won't poke a hole either ...

Always interested - please post what you find. Thx

[Frank Brunot]

First, a piece of 3/8" OD clear tubing, with a couple turns of tape wrapped around it, works for inserting into the NACA vent tubes. It seems BOTH the AUX vents were blocked by now dead bugs. You can blow in the tube, but the minute you block the second 3/16" tube coming out of the wing (the second leg of the "Y"), you can't blow anymore. So the blockage was above the "Y". I used a LONG (11") 1/8" drill bit and went up through the straight 3/16" tube, and ran into a stoppage about 5-6" in. SLOWLY rotating the drill bit brought dead bugs and other debris out of the NACA tube. The drill bit finally broke thru, and went into the vent to about the 10" point, at which point it hit the bend in the vent tube. I can now blow air into the AUX tank thru the NACA vent with the small 3/16" tube blocked off.

Some sort of a flexible "roto-router" would work great, but have never seen one. I really need something 3/8" diam to go up thru the NACA vent tube to fully clean it out. If I find something, I'll post it.

[N3322G]

Hearing about the bugs reminds me of the dirt daubers who clogged the sump tubes under the selector - overnight in our previous mechanic's hangar - it was a real surprise not to be able to sump. We were in a good place for that to happen though.