Grouphead temperature recovery time

by **mindless_fool** on Wed Jan 26, 2011 11:07 am

I got a EricS grouphead thermometer on my Vibiemme Domobar super hx electronic. When i turn on the machine and let it heat up the thermometer reads 202 til i make a shot then it goes up to 206, but after my shot it drops down to 195 and stays around there for a long time before climbing slowly back to the 200 range (from what i understand the temp of the water is 5 degrees lower then what the thermometer reads). My question is ... shouldnt it go back up closer to 200 fairly quickly? or do i have a problem somewhere.. i did a descale a week ago and backflush somewhat regularly with cafiza.

thanks for any info guys!

by **gscace** on Wed Jan 26, 2011 11:47 am

Presumably the group is e-61 style, right? It takes a little while for the thermosyphon loop to get started again after brewing, so what you observe doesn't surprise me.

-Greg

http://users.rcn.com/erics/ · by **erics** on Wed Jan 26, 2011 11:55 am

The Vibiemme Domobar Super Hx models are equipped with a thermosyphon restrictor of ~ 2.8 mm diameter in the upper group tubing feeding the grouphead. IIRC, this restrictor is located where the tubing joins the hx outlet.

In addition to slowing down the thermosyphon action and thus reducing grouphead temperatures dramatically, this restrictor, to some extent, controls the mix of water entering the group from the two ends of the hx.

Do you do a "screen flush" at the conclusion of your 1st shot or prior to your second shot or BOTH?

What is the maximum reading on your pstat after the machine is FULLY warmed up?

Is this "slow crawl" back to ~ 200 F a new phenomena or is this the behavior from initial installation?

How "slow" is slow? How large or small is your shot? What sort of duty cycle do you want from the machine?

by **cannonfodder** on Wed Jan 26, 2011 12:10 pm

That is normal with VBM's due to the flow restrictor. The heat exchanger water heats much faster then the group head. That is in part why the VBM's have such a short flush and flat brew temperature. That thermosiphon restrictor keeps the brew group at a lower temperature which helps to stabilise the brew water as it goes through the group. VBM's have very large brew groups which adds to the heat sink effect. On the down side, a short 3 second flush after a shot has also been know to stall the thermosyphon. A good practice, when you flush the group after a shot, run it for 5-7 seconds. That is usually enough time to address the stall problem for me. You can do a search for thermosiphon stall if you want more information about it.


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