When do you use a blow off tube?

[ncbrewer]

I transfer some hop material to the fermenter. Once, I had an explosion even with a blow-off because hop material plugged it. The arrangement was just a drilled stopper with the tube pushed through it. I don't remember the tube ID. But I'd recommend a large ID tube if you have hops in the fermenter.

 

[Tegra]

Fermcap = zero blowoff + good head

 

[blizz81]

Fermcap = zero blowoff + good head

Here's a pic of my imperial stout with ample fermcap + ample headspace (5.1gal in a 6.5gal carboy) + temp management (measured temp inside carboy w/Thermoworks probe at time of peak ferment = 65*F).


https://goo.gl/photos/iFaR2VEE3nZdasbP7

 

[Kharnynb]

only with very big beers and abbey yeasts, otherwise i tend to trust that 20 liters in a 30 liter fermenter is enough headspace.

I mostly use notty though, so i tend to be familiar with it's activity.