I used to run a valved reflux / pot combination still. If I ever had a brain fart it would have been possible to close a wrong combination of valves. For this reason I put in a safety bypass valve and connected the blowout output back into my condenser. I really object on principle to the concept of venting flamable gasses into my still room.
This was an experimental still that has subsequently been salvaged for parts, but it proved a point. These type of safety relief valves, usualy with 1/2" or 3/4" fittings that are intended for steam or water, will work perfectly well for alcohol vapour. They also work on steam injection rigs and steam mashing setups. IMO they are a better option than the jiggle weights that you see on pressure cookers because they give you the option of venting the flamable vapours to a safe location. For still use I would only use them on cleared washes with no solids in the boiler. I installed mine fairly high up the vapour path (connected to the condenser air vent) through neccesity (between 2 valves) but a better location would be high up in the headspace on the boiler.
In reality you would only ever need one if you managed to block your condenser, and that is determined by your condenser design. I use multiple small diameter worms on my pot still so it is conceiveable that I could suffer a blockage. (I am about to incorporate a puke box - but the concept is still valid) For sugar, rum, cleared fruit washes etc these valves should work fine. The minimum input is 1/2" which should pass foam OK.
However, I am also building another pot still specifically intended for distilling ON the grain. Now I am taking the precaution of using a glycol double boiler so I would have to really screw up to get a puke, but it is possible. Now some other folks might be distilling on the grain and heating by other methods - or considering it, and for them this really should be something they are thinking about. It is unlikely that these valves would cope with a grain puke.
My condenser on the still in question is a coiled liebig with 3 of 10mm vapour paths in the same 1" jacket. Now if I ever blow grain into that I suspect I will be in BIG trouble.
One simple solution is a nice big 2 or 3" diameter cork that you can blow out of the pot. This will make a hell of a mess, but much less than if you explode your boiler. Off course in addition to grain you will expel flamable vapour into your still room. Always a bad idea and worse if you are heating with gas.
This probably is only relevant to a few folks out there. Most all grainers probably clear the mash and just distill the liquid, but some might wish to distill on the grain. For those small few how are you dealing with the issue?
I haven't dsecided yet but I am considering using the blow out cork method - but blowing it into a puke box so I can capture the grain AND subsequently vent the vapour to a safe location. Bursting disks in a tube big enough to cope with a grain discharge might be another option.
Off course the best option is to make sure it never happens in the first place. This is probably more important for distilling with solids in the boiler than for any other method. I am coming round to the idea that I would like a sightglass so I can watch the conditions in the boiler (this is just for stilling on the grain) AND a manual valve so I can bleed off some vapour if the boil gets too violent. Thick mashes tend to hold the heat and do not respond as fast as cleared washes if you just turn down the power input. And off course with glycol there is a time lag anyway - the glycol is a big thermal buffer that holds in the heat.
So although this might be of limited value to the majority of folks out there, what do you think, and for those on the grain stillers how are you approaching the issue?
Gives a warning, without the danger of escaped vapours floating around. Set it up so any condensate out of it has to fall some distance into a metal bucket, so it makes a decent sound to warn you.