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Erratic Brew Pressure on Vibiemme Domobar Super
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danield
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Joined: 16 Apr 2014
Posts: 3
Location: Israel
Expertise: I love coffee

Posted Wed Apr 16, 2014, 12:44am
Subject: Erratic Brew Pressure on Vibiemme Domobar Super
 

Hi,
My Domobar used to brew at a near constant 12 Bars of pressure throughout the brew cycle. A couple of days ago the brew started to get extremely weak with the gauge jumping between 8 and 11 a few times during the cycle, with the sound and coffee flow to match.
Right before this happened I replaced the in-tank water softener so I thought it might have something to do with it. I tried brewing one time without it but still no change.
Any ideas?

Thanks,
Daniel.
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frcn
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frcn
Joined: 23 Dec 2001
Posts: 3,349
Location: Northern California
Expertise: Professional

Espresso: Vibiemme Domobar Double
Grinder: Mazzer Kony, Baratza...
Vac Pot: Hario, 2 Cory pots, 1 Cory...
Drip: Behmor Brazen, Bunn A10 mod...
Roaster: computer controlled Hottop,...
Posted Wed Apr 16, 2014, 9:06am
Subject: Re: Erratic Brew Pressure on Vibiemme Domobar Super
 

Access teh pressure relief valve, remove the screw, spring, and piston, Clean and lube it, and check the bore of the body for foreign matter, corrosion, and scale before assembly.
But brewing at 12 BAR? That's pretty high unless there is something wrong with the gauge.

 
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boar_d_laze
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Joined: 21 Nov 2006
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Location: Monrovia, CA
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Espresso: La Cimbali M21 DT/1 Junior...
Grinder: Ceado E92; "Bunnzilla"
Vac Pot: Royal Coffee Maker
Drip: Chemex + Kone; Espro Press
Roaster: USRC Sample Roaster
Posted Wed Apr 16, 2014, 9:43am
Subject: Re: Erratic Brew Pressure on Vibiemme Domobar Super
 

frcn Said:

Brewing at 12 BAR? That's pretty high unless there is something wrong with the gauge.

Posted April 16, 2014 link

+1.

Way too high.  Vibratory pumps increase pressure with load, and (a nice thing about that), pressure can be used as a diagnostic.  12bar means a lot of load, which strongly implies you've got the grind/dose dynamic screwed up to the point where you're over extracting by quite a bit (over extraction -> bitter).

You want a pressure reading which goes almost immediately to 9 (ideally, but 8.7 - 9.7 is OK) and stays there through (or very nearly through) the duration of the shot.  A pressure drop indicates channeling.  High pressure indicates a grind which is too fine or an over dose.  Low pressure indicates a grind which is too coarse.  Gradually dropping pressure indicates an under dose.  Etc., etc.    

Rich
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danield
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Joined: 16 Apr 2014
Posts: 3
Location: Israel
Expertise: I love coffee

Posted Wed Apr 16, 2014, 9:54am
Subject: Re: Erratic Brew Pressure on Vibiemme Domobar Super
 

Somehow I got it in my head that 12 was the desired pressure so I upped the ground dosage and tamping pressure a while ago...
frcn - do you know of a (visual) guide for cleaning the pressure relief valve? (is it the valve on top of the boiler on the side opposite the pressurestat?)
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boar_d_laze
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Joined: 21 Nov 2006
Posts: 1,070
Location: Monrovia, CA
Expertise: I live coffee

Espresso: La Cimbali M21 DT/1 Junior...
Grinder: Ceado E92; "Bunnzilla"
Vac Pot: Royal Coffee Maker
Drip: Chemex + Kone; Espro Press
Roaster: USRC Sample Roaster
Posted Wed Apr 16, 2014, 10:18am
Subject: Re: Erratic Brew Pressure on Vibiemme Domobar Super
 

danield Said:

... so I upped the ground dosage and tamping pressure...

Posted April 16, 2014 link

Tamp pressure rarely affects more than the first few seconds of the shot -- especially with pre-infusion (which is a part of your E-61 group).  

If you're getting an appropriate flow rate and brew ratio, you may want to tighten the grind as you reduce dosage.  But keep your "eye" on the balance of bitter and sour, as well as on assertiveness.  

Rich
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frcn
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frcn
Joined: 23 Dec 2001
Posts: 3,349
Location: Northern California
Expertise: Professional

Espresso: Vibiemme Domobar Double
Grinder: Mazzer Kony, Baratza...
Vac Pot: Hario, 2 Cory pots, 1 Cory...
Drip: Behmor Brazen, Bunn A10 mod...
Roaster: computer controlled Hottop,...
Posted Wed Apr 16, 2014, 4:35pm
Subject: Re: Erratic Brew Pressure on Vibiemme Domobar Super
 

danield Said:

Somehow I got it in my head that 12 was the desired pressure so I upped the ground dosage and tamping pressure a while ago...
frcn - do you know of a (visual) guide for cleaning the pressure relief valve? (is it the valve on top of the boiler on the side opposite the pressurestat?)

Posted April 16, 2014 link

It is NOT the valve on top of the boiler. See THIS post and THIS post and THIS post. Remove case and (iirc) possibly the divider(?) and put a towel under the machine. Unscrwew the but slotted screw thing and remove it. Pull out the spring and remove the piston inside the valve (it just pulls out). Check condition of the spring (and be sure it is one of the newer ones), clean the piston and bore, replace the O-ring if necessary, lube with Dow 111 which is called something else now, and reassemble. Use a blind filter and adjust the valve by turning the screw one way or ther other to get a max of about 10.5 to 11 (I do not recall the best setting offhand). 12 is just a screaming prayer for over-extraction.

 
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danield
Senior Member


Joined: 16 Apr 2014
Posts: 3
Location: Israel
Expertise: I love coffee

Posted Fri May 2, 2014, 11:56pm
Subject: Re: Erratic Brew Pressure on Vibiemme Domobar Super
 

Thanks for your help everyone. At first the technician also though it was the pump but after testing with a blind flush it turned out to be fine. The erratic pressure was apparently the result of improper grind/tamping etc..
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frcn
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frcn
Joined: 23 Dec 2001
Posts: 3,349
Location: Northern California
Expertise: Professional

Espresso: Vibiemme Domobar Double
Grinder: Mazzer Kony, Baratza...
Vac Pot: Hario, 2 Cory pots, 1 Cory...
Drip: Behmor Brazen, Bunn A10 mod...
Roaster: computer controlled Hottop,...
Posted Sat May 3, 2014, 9:12am
Subject: Re: Erratic Brew Pressure on Vibiemme Domobar Super
 

As it often turns out, most espresso problems are caused by a loose nut behind the portafilter handle.  ;-)

 
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