I think it would definitely be best to have some sort of an insert to ensure that the surface is flat for the o-ring seal.
The shedule 40 pvc is 26.67 mm OD and 20.42 mm ID. I've got a friend in a machine shop, so I think I'll have something machined a little sturdier (brass or stainless steel?): 35 mm OD; 22 mm ID; 17 mm thickness
The inner wall around the hole is convex (I'm not sure if it was originally, or if that's from me tightening it down & pinching the walls together). A larger disk/insert would only really be supporting a few mm around the hole anyway.
I still think I'll fill the surrounding space with something supportive as well.
Fibreglass resin exothermic as it cures, and I'm afraid that much between plastic might get too hot. It shrinks as it cures form the inside out as well (so it would pull away from the walls).
RTV (room temperature vulcanizing) silicone, with platinum catalyst for an addition cure rather than a condensation cure (since it's deep & sealed), seems to be what I want. I'll need less than 4 oz, but it seems to be sold by the pound ($40 CAD).
One option I can think of is polyester resin, aka BONDO which is what auto body shops use to fill dents, etc. You could even just dig out whatever insulation you can via the hole the assembly is going to fit into and fill that new space with bondo or that epoxy stick that has the green skin with white center. The idea is to create a rigid "donut" to hold the inner and outer walls of the cooler apart when you tighten down.
If this is done correctly, there should be no worry about food safe or not because the wort shouldn't touch it.
The problem with fibreglass resin is that can generate a lot of heat and it cures from the inside out. So it would shrink away from the walls as it dried. It would also be very permanent.
The RTV silicon is food safe, has minimal shrinkage, and should seal it up as well. But it's pricie.
I've currently got it together with a delrin spacer and no other filler. I figured I could see if it leaked this way... and I may just leave it like this. But man is the 'xtreme' inner wall thin! I didn't use an o-ring, I used a thicker rubber washer from the faucet section to try & spread out the load a little. The inner wall compressed nicely against the inner spacer.
I wouldn't go smaller than 35 mm OD for the spacer. When the cooler is full of water, the inner wall is pushed up against it. It doesn't seem to be bulging around it though.
By the way, 2.5" pipe nipple was a good length. Lock nut with rubber washer on the inside; big stainless washer on the outside with another lock nut. Once you know it all fits, I suggest threading the ball valve on first (before inserting the assembly).
I was hoping to not have any teflon, but the hose adaptor on the ball valve is dripping.
Not to piss in the punch bowl, but this design can still leak if the o-ring isn't tightly sealed around the nipple (and once you compress the o-ring, especially if you over compress it, they have a tendency to squeeze out). There isn't anything putting external radial force on the o-ring towards the nipple. So, the design isn't inherently leak-free, even though it may be more leak free than most designs. It's certainly more leak free than the weldless set-up on my HLT. That thing leaks like a sieve.
Perhaps you could add a 3rd washer between the cooler inner wall and the existing stainless washers that would have a slightly smaller ID than the OD of the outside of the o-ring. That way you would have the o-ring completely captive, and compressed on both of the sealing surfaces. It might be overkill, but it would slightly improve the design.
The easier improvement on the design is to use a flat silicone washer that fits around the nipple snugly. It won't be squeezed out. The intent of the design was to solve two major problems with the popular designs. Putting the oring over threads. Clamping two thinwall pieces of plastic together with no internal support.
I used this design more or less for my MLT. A few brews ago I accidentally dropped my MLT from my two-story deck onto the brick patio below (empty). It still does not leak.
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The easier improvement on the design is to use a flat silicone washer that fits around the nipple snugly. It won't be squeezed out. The intent of the design was to solve two major problems with the popular designs. Putting the oring over threads. Clamping two thinwall pieces of plastic together with no internal support.
The flat washer is probably better, but I still think leaks are possible with that setup. Unless the gasket is radially compressed, there is leak potential.
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