Main line fuel filter

[Bandit 286]

Replaced my main line fuel filter with one of those $13 screen filters from Napa. Last night I was going to go flying. When priming I noticed air in the primer line, enough to give it a couple of more shots to get it primed and started. Once started there were supper big bubbles coming out of the filter and going up into the carb lines. I had a couple of hours on this filter. Didn't like that so I replaced it with a new paper filter again. No major bubbles in the primer line or the fuel lines going to the carbs. No gas leaking out of the Napa filter, but why all the bubbles?

[dynomike 91]

my guess is air being sucked in by the fuel pump through a small leak in the filter .my plane quit on its first flight because of a small air leak on a filter .fuel pumps sucked the air and drained the header tank.test pilot shut all electrical off then it started it gravity feed and flew it back(he was at 9000ft). or its  something else completely j,just what came to mind

[Bandit 286]

I am thinking if there was a air leak in the filter gas should be leaking out also.

[Av8r3400 1179]

It may have been in such a place as to have an o-ring or some other part of the filter act as a one-way valve allowing air to be sucked in but not let fuel out…  ??

 

I've seen this before in hydraulic fittings.

[lostman 198]

If you're talking about the glass style filter, I have one on my other aircraft. It always has a little air in the glass but it pulls through just fine. Not sure if it just captures air and the way it pulls it leaves the air in the glass area or not. The filter element is connected so that I can understand internally how it could leave the air in the line without sucking it into the carbs. My carbs are also bowl style so I've never worried about it. I've flown over 50 hours with this set up without so much as a hiccup.

[EDMO 1078]

On the suction side of the pump, it will pull in whatever is easier, like air, or a mixture of what is available -

On the pressure side of the pump you would have fuel coming out of the leaking part.

EDMO