CMA thermal management

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DougCanuck

#1: Post by DougCanuck »

Has anybody come up with a way to preheat/control the temperature, of a CMA group head?

My plan is to build a double boiler lever machine using a CMA group head. I think its important to accurately control the temperature of that big chunk of brass the brew water is going to flow through.

Any thoughts or opinions would be much apprecited.

pizzaman383
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#2: Post by pizzaman383 »

Check out the open source lever thread. Basically, you can heat a plate that you bolt up to the group head.
Curtis
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“Taste every shot before adding milk!”

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MemPast

#3: Post by MemPast »

I might add this thread to the list of readings, too:
Strega-fying my Brugnetti Aurora, AKA a non-invasive way to add group heater to any lever machine

Of course, the aurora group is bolted to a boiler, so the poster is trying to speed up heating the group. It "might" suffice for heating up the group!

Paolo

#4: Post by Paolo »

This certainly does work well...on the Brugnetti Aurora at least.
I have had an Aurora with Sam's ingenious modification installed for over 2 years now. It hasn't missed a beat.

From cold, the group gets to operating temperature around 5 minutes after the pressurestat kicks in and turns the heater off. This is between 15 and 20 minutes...as opposed to 45 to 50 minutes without the modification.

I have set the controller to turn the silicone heater blanket off several degrees below operating temperature, so that the heat generated by the Aurora's heating element takes over and the heater blanket is only ever in use for around 15 minutes at a time.

Of course, you could set the controller's temperature say 10 degrees higher than the group's normal idling temperature if you wanted to.

DougCanuck (original poster)

#5: Post by DougCanuck (original poster) »

Thanks for the suggestions. I've been reading various threads that have helped my understanding

My intention is to run an independent brew boiler fed by line pressure, to make up for the the lack of pressure from a boiler at less than boiling temperature. Eliminating the need for a reservoir also has the benifit of reducing the foot print of the finished machine.

I'm hoping to find find enough room in the casting to drill a hole or two for cartridge heaters in the neck of the the GH. Do you know if anybody has gone this route?

Paolo

#6: Post by Paolo »

This is the only mention of heater cartridge/s installed in the CMA group that I am aware of:-
https://coffeesnobs.com.au/forum/equipm ... ille/page8

so it has been (and can be) done.

pizzaman383
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#7: Post by pizzaman383 » replying to Paolo »

I hadn't seen this one. That is pretty ingenious.
Curtis
LMWDP #551
“Taste every shot before adding milk!”

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DougCanuck (original poster)

#8: Post by DougCanuck (original poster) »

I had a thought over night. Because i plan to install two boilers, why not plumb in a bypass valve from the steam boiler to the GH, to heat it with steam. I could mount a thermocouple in the GH to monitor the temperature rise, so that I know when to close the valve.

Once the GH is up to the temperature i choose, it would never overheat from pulling consecutive shots because the water is coming from the separate brew boiler.

Too simple. Am I missing something?

pizzaman383
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#9: Post by pizzaman383 » replying to DougCanuck »

That would be uncharted territory so you would need to do some experimentation.
Curtis
LMWDP #551
“Taste every shot before adding milk!”

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homeburrero
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#10: Post by homeburrero »

DougCanuck wrote:why not plumb in a bypass valve from the steam boiler to the GH, to heat it with steam. I could mount a thermocouple in the GH to monitor the temperature rise, so that I know when to close the valve.
Condensing steam can transfer a lot of heat, much more than a conventional thermosyphon loop. I played around with that idea on a plain E-61 HX by draining lots of water out of the HX and watching it recover. My group that normally idled at 203F (EricS group thermometer) gradually climbed to over 220F. I think you would need a loop, so that condensed water in the group drains back to the steam boiler. You certainly want a valve to shut off the loop when the group gets too hot.

The gen 2 LP Europiccola and Pro had a small steam vent to the top of the group and were known for idling a little too hot. They got rid of that vent with the Millennium group, and lately some gen 2 owners have been retrofitting kludges that block that vent.
Pat
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