PID or pressurestat upgrade for HX machine

[skyryders90]

I'm looking to make a couple of upgrades to my Bricoletta. First is to put a decent vacuum breaker on it (it gets horrible vapor lock when heating up). The second is to upgrade the heating control. This machine has a 1.5L boiler and a 1800W heating element, so it heats up pretty darn fast. This is coupled, however, with a pretty darn cheap pressurestat - no deadband adjustment, etc. It cycles a LOT, and this sometimes will cause some boiler pressure fluctuations that you have to surf around when pulling shots (malachi mentions this in his review). So, here's my question:

Should I upgrade to a Sirai pressurestat or should I just go all the way and PID it? Is there any real point to PID'ing a HX machine?

I'm mostly looking to elimate the big dips, but anything to reduce cycling would be good, too. While I'm at this, I'll probably insulate the boiler, which should help some on the cycling side.

Any suggestions?

[AndyS]

I'm mostly looking to elimate the big dips, but anything to reduce cycling would be good, too. While I'm at this, I'll probably insulate the boiler, which should help some on the cycling side.

Insulating the boiler will save energy and reduce cycling. But, contrary to the conventional wisdom, insulation will INCREASE temperature overshoot and make tight boiler control more difficult (with or without PID).

[skyryders90]

Insulating the boiler will save energy and reduce cycling. But, contrary to the conventional wisdom, insulation will INCREASE temperature overshoot and make tight boiler control more difficult (with or without PID).

OK - that makes sense. Do you think there's any real advantage to PID'ing a HX machine? It completely makes sense to me in a machine where you have a brew boiler, but perhaps less so in a HX scenario. I'm just looking for a bit more control in element cycling, deadband, etc. My thinking was that if I was going to drop the $$ to put in a Sirai, then it's not THAT big a jump to just PID it (certainly it's a good bit more, but why not do it up right).

Is there any solution that can drive the heating element at something less than full-on?

[HB]

Do you think there's any real advantage to PID'ing a HX machine?

No, I don't think so.

Your Bricoletta relies on the group's thermal mass to "fine tune" the final temperature, essentially (a) slowing down the effect of the flush enough so you can reliably obtain the same brew temperature and (b) keeping the temperature stable during the extraction. I doubt an extremely accurate boiler temperature will translate into more accurate brew temperature because (a) the cooling flush plays a larger role in the final temperature entering the grouphead, and (b) the group relies on the cooling flush / final brew temperature as much as the thermosyphon's contribution. This last point wasn't evident to me until I started measuring with the thermofilter for numerous trials. It seems obvious now, having mulled over the fact that the group idles below brew temperature... something else is determining the final-final group temperature... the brew temperature is more accurately obtained after several shots... hmm-m.

The group temperature or the cooling flush / brew temperature... who's tuning whose temperature? Answer: Both.