Primer line failure...again

[Mile High Relic]

Originally Posted by deek

If you take the airbox off and have someone pump the throttle you'll see it takes a few seconds for gas to begin dribbling from the carb throat.

deek

This is always what I assumed was happening, and in reading through this thread I started thinking it would be a good experiment to run next time the FAB is off the plane.

My O-360 starts well cold with a single throttle pump immediately before cranking. No pumps when it is hot.

[flyinmonque]

.......Heat your copper lines to red hot and let slow cool?

[YellowPeril]

Huh. I've been running an Ellison TBI (no accelerator pump) for 10 years and 1,000 plus hours. I have copper primer lines going to all 4 cylinders, and haven't had a single issue (save a small leak at a Tee once).

I couldn't possibly tell you what I've done right....would you be interested in photos?

[Bluebeard]

Resurrecting this old thread.

My O-320 has 1/8" copper primer lines to all cylinders. These have periodically broken, not a good situation to be inadvertently spraying fuel into the engine compartment.

Having just repaired a copper line again, I wonder if there is some other more flexible tubing available and suitable for this application?

[I know there is a common view here that priming is unnecessary, but let's put that to one side for a moment ....]

[rmarshall234]

Originally Posted by flyinmonque

.......Heat your copper lines to red hot and let slow cool?

Yes, you might try annealing the copper as mentioned here. The reason they crack is they get work-hardened.

[RV-4]

Same set up as Yellow Peril, same results.

Bruno

[lr172]

Originally Posted by Mel

Yes, but remember gasoline will not burn. It's the vapors. And the vapors don't drain. Even with the fuel drained from the air box, there is still a very real potential for fire.

Not true! When presented with a flame gasoline burns just like ligter fluid. It's true that only vapor can ignite from a spark/ignition source. However gasoline burns quite nicely when lit by a flame. Ever watch a car fire?

[BillL]

Originally Posted by lr172

Not true! When presented with a flame gasoline burns just like ligter fluid. It's true that only vapor can ignite from a spark/ignition source. However gasoline burns quite nicely when lit by a flame. Ever watch a car fire?

Actually, it is the vapor that is burning. Example. Fill a quart milk bottle with gasoline, right to the top. Then make sure the outside is free of wetted area (no vapors , then take it to an area 30 ft from anything you don't want burned. Then take a match and light the top. It will burn the vapors coming off the liquid surface. A nice small flame. As the level burns down, and the liquid is heated, it will soon boil, then you have a roaring flame, but it is still the vapor that is combining with oxygen to burn, the liquid is still sitting down there in the container, just a reservoir. I had fun doing this test. It is not for the faint of heart. It could be hazardous to your future if handled poorly. Proceed at your own risk. etc etc.


To the topic - copper can live nicely if properly brazed/soldered and fastened to avoid vibration that will harden and fail the material. The focus should be on the attachment points. Not the material.

[lr172]

Originally Posted by BillL

Actually, it is the vapor that is burning. Example. Fill a quart milk bottle with gasoline, right to the top. Then make sure the outside is free of wetted area (no vapors , then take it to an area 30 ft from anything you don't want burned. Then take a match and light the top. It will burn the vapors coming off the liquid surface. A nice small flame. As the level burns down, and the liquid is heated, it will soon boil, then you have a roaring flame, but it is still the vapor that is combining with oxygen to burn, the liquid is still sitting down there in the container, just a reservoir. I had fun doing this test. It is not for the faint of heart. It could be hazardous to your future if handled poorly. Proceed at your own risk. etc etc.


To the topic - copper can live nicely if properly brazed/soldered and fastened to avoid vibration that will harden and fail the material. The focus should be on the attachment points. Not the material.

While I believe you are technically correct here, I still think it is wrong to give someone the impression that liquid gasoline won't burn, regardless of what is technically happening. I could also argue that it is not the gasoline burning, but in fact a combination of gasoline vapor with oxygen that is burning. That shouldn't fool me into thinking that gasoline won't burn. I believe the gasoline is continuously converting to vapor until the surrounding air is saturated and therefore always a risk unless you happen to be in a vacuum chamber.

Larry

[Bluebeard]

I know the copper is getting work hardened - in my case in spite of it being well supported and with strain relief loops etc; it is inevitable that there is movement when attached to the engine. My earlier question was whether any of the pundits here can suggest an alternative material?