I recently posted in the tasting room about my experiences in dialling in to extract a particular CS blend from the BZ10 (the help was much appreciated). In the process I noticed the BZ10 would occasionally clunk and momentarily lose pressure while pulling a shot, as seen at 8-9 secs in the following video.
Has anyone seen this before / able to have a stab at the cause? It doesn't occur on every shot, but I have had it happen across different PFs and different baskets, and even with a blind basket. It seems to happen less when I have the PF handle turned past 90 deg ... which makes me suspicious that I'm momentarily losing seal at the group head and the PF then reseats and reseals ... Luckily the shots still taste good tho
Might be the Overpressure Valve.
The noise seems to coincide with the first blush of liquor to pour.
IIRC Sponosrs Antony and Renzo are both Bezzera (stockists) specialists.
They will prob check in tmrw.
Nice pour by the way!
Could be the Autofill Solenoid kicking in when it detects the boiler needs filling.
Don't think there's any reason for concern...
Id say opv too. You cat see the pressure needle drop as the opv opens and then the pressure rise again after it closes.
The other slightly earlier click..not sure. The needle doesnt react so id say its not on the brew circuit
The OPV doesn't actually operate in a Binary format...
Rather it slowly releases water as the pressure builds up to its preset.
Well id say its sticking then. Watch the needle. Its not smooth at all.
I think a pour without the clunk would show a steady needle.
Thanks for the ideas to look at. The problem sometimes happens while pressure is increasing (well before the 12 bar set limit), which I thought might reduce the chance of it being the OPV.
I ended up speaking to the fellows at Barazi on the phone, and they suggested it was related to the BZ10 group head seal being a particularly soft rubber, and have kindly sent me an alternative seal to try. They said it was a not an uncommon BZ10 characteristic, though mine was one of the more prominent cases.
Certainly turning the portafilter handle a long way past 90 degrees (e.g. 135 degrees) to really tighten up on that seal does appear to solve the problem ... but of course then my spouts are pointing the wrong way! So a harder group head seal it is.