Here is excerpt of a support ticket with a customer (Ben) about this....
Your logic is not flawed.
However, there's really little reason to have positive pressure on the Bucket. If you leave your Air-Lock in place, and filled to the correct level any O2 entering the bucket will be sanitized as it passes though the air lock. The small amount of O2 pulled in, will set on top of the CO2 layer inside the bucket and not come in contact with your beer.
The buckets were never designed to take a positive pressure. In a worst case situation, the lid may deform (it isn't domed) and /or result in a less than 100% safe situation - which is why we recommend not to do it.
Peoples130 about 1 hour ago
Thank you for the quick reply, that information is very helpful.
What I was thinking was to hook my co2 line up to the fixed blow off elbow using a piece of 1/2 silicone tubing. This would allow me to get gas into the fermenter, but it would be a loose enough connection to fail before say, the fermenter blew up. I would then just set my regulator super low at like 1 or 2 psi. This would at least ensure that positive pressure would remain in the inside of the fermenter and as the temperature dropped more co2 would enter the fermenter , instead oxygen finding its way in.
I read somewhere that a PET carboy is is rated at 15psi, so I figured a stainless bucket could stand up to 1psi (this could be terribly flawed logic and is really just a guess).
Anyways, your information makes crashing with the blow off assembly in place sound a whole lot safer.
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Ss Support Team Agent M Yesterday 12:27
The Bucket material is a very robust 18 gauge ss, don't think this is such a concern. When you say lightly pressured, what does that mean and how would you control it? Just curious
Peoples130 Yesterday 09:53
If I were to try and cold crash in a brew bucket with the sealed blow off kit in place, would that cause any issues? My main confer wold be causing the bucket to buckle as the temperature dropped and air could not get into the bucket (which is what I am trying to avoid anyways). I would lightly pressurize the bucket to avoid this, but that doesn't seem to be a recommended plan of action.