... or ±0.x bar gauge variation, altitude and local pressure

did you run some test shots WITHOUT any flush?

Yes, but not very systematically. I seem to recall that the temperature after a long idle seemed to roughly correspond to the PID display. Kind of convenient if you want to just walk up and make a shot and aren't too fussy, as long as the PID is set to some midrange value. It does not overheat at idle. The BZ07 is the only machine I have owned, but my understanding is that this behavior is quite different from the idle temperature behavior of most HX's.

But I still use flushing to control the temperature.

Actually to clarify, I meant the first shot off idle is not super hot, but the HX water definitely is. I assume it gets enough cooling passing through the (partially heated) group that it exits at a reasonable temperature.

My BZ35 has similar construction with the tiny heat exchanger and conduction heated group. I had a lot of trouble getting consistent shot temperatures because of the sensitivity to flush timing. The group took forever to warm up and the final temperature was affected significantly by ambient temperature.

I decided to tinker with the old machine and add a PID controlled heated group. This mod in conjunction with my preifusion mod (described in another post) really improved the performance in spite of my limited barista skills.

Nice work Eric!

Mark

If the BZ07 has a cartridge heated group, and the problem of Bas is kind of the opposite, the group overheat to kickly, how about a thermostat with lower temperature at the group? Maybe around 75C, so the group cycles between 70 and 80. If you look for "KSD301" at ebay.com, there is a lot of this small thermostat from Hong Kong...

Well, this could help with the flushes, but maybe not with the rising temperature during shot. For that, maybe only this great mod Eric did on his BZ35 could help.

Or, another idea, but much more drastic: a cold water input near the water inlet of the group, maybe with a solenoid or maybe with a check valve, and a needle valve to regulate the cold water flow. Something like the thermosyphon when pulling a shot but without the fuss about how the loop heats the group, just the new variable "cold water flow"

Márcio.

Carneiro wrote: rising temperature during shot

If the rising is one or two degrees it's not a problem I guess...if temperature rises from about 92 to 97 degrees in the 2nd half...that's maybe too much...

Is Eric Svendson has sayed before putting a PID on the group head would make sense...in that way you can manage the balance between HX and GH by yourself....

edit: made a double shot at 90 degrees Celcius PID setting/1,0 bar boiler pressure: without a flush temp is 92 degrees at 15 seconds and slowly rising to 94 degrees at 25 seconds....rising seems to be significant smaller compared to 1,2-1,3 bar...only one shot, so needs to be duplicated! (at 1,0 bar flash boil from idle about 5 seconds; steaming performance still enough for a double cappuccino)

Yes, a PID on the group heater would be more adjustable and consistent. Just a little more costly.

Nice to hear about 1 bar pressure and more stable temperature. I think 1 bar to steam low volume of milk is great, depending on the steam wand tip.

Márcio.

did you run some test shots WITHOUT any flush?

I just realized that earlier I didn't answer the same question that you were asking. So I ran a few shots with no flushes, at 1.5 bar:

1- after long idle: 94.3C
2- after 5 minutes: 92C
3- after 5 minutes: 95C
4- after 5 minutes: 92.5C

Sorry, I can't explain the inconsistency. These are much less consistent than I have seen with flushing.

cpreston wrote:Sorry, I can't explain the inconsistency. These are much less consistent than I have seen with flushing.

maybe just because of the flushing! by flushing to x seconds past flash boil GHT rises more or less to the same temperature every time...without flushing GHT can be anywhere between 83C and 89C on my machine...hypothesis: a delta of 6C in GHT will have influence on shot temperature because of thermal mass?

my routine at the moment: boiler pressure 1,0 bar, a 5 second flush to end of flash boil, lock and go...shot temperature 91-92C at the start slowly rising to 93-94C at the end of an double (92-93C when making a single)...

edit: just lock and go without any flush doesn't give too high temperatures but temperature is less predictable...starting anywhere from 90C tot 93C degrees...

question: someone told me that changes in brew pressure by adjusting the OPV can result in pressure build up in the group; flash boil is no due to super heated water entering atmospheric pressure but due to release of pressure build up...does this make sense to you? I don't understand