Beer line self-emptying with polypropylene?

[Stephonovich]

I recently started switching over my kegerator lines from vinyl to polypropylene, and I've noticed an issue - the beer seems to drain back into the keg slowly, such that when I go to pour, there's a hugely excessive amount of foam. Is this because there's less friction as compared to vinyl? I never had a problem keeping vinyl lines full.

 

[day_trippr]

If you're keeping the keg under pressure, the only way the beer can appear to be running back into the keg is if CO2 is displacing it.

That can be caused by too low a dispensing pressure to maintain the original carbonation level (so CO2 breaks out of solution); temperature getting too warm to hold that carbonation level (so, again, CO2 breaks out of solution); or a bad Out dip tube o-ring under the flange, allowing CO2 in the keg head space to take a short cut into the beer stream under the Out post...

Cheers!

 

[Stephonovich]

It happens on multiple kegs that I've swapped, so I doubt it's an o-ring issue.

Temperature seems the most likely suspect, although that still doesn't explain why I never saw the issue with vinyl lines. More surface area with the poly ones, since they're longer?