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Low Brew Pressure (Bezzera BZ10)
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jferreir
Senior Member


Joined: 23 Apr 2014
Posts: 16
Location: Toronto
Expertise: Just starting

Posted Mon May 19, 2014, 4:58am
Subject: Low Brew Pressure (Bezzera BZ10)
 

I posted a similar thread at Home-Barista, but I haven't found a solution yet. I'm hoping the kind folks at CG can change that!

Briefly, I have a new Bezzera BZ10 HX machine, with the OPV factory set at 12 bar. When I use a blind filter, the bar pressure steadily climbs to 12 bars and holds. However, when I attempt to extract coffee, the brew pressure normally reaches about 8 bars, and then drops between 4-6 during extraction; the result is sour/under-extracted coffee. I've adjusted both the grind and dose, but to no effect. For example, the grind can be so fine that there's no coffee flow at all, and yet the brew pressure still maxes out at about 8 bars. I should note that I'm using fresh beans from a local roaster, and I've experimented with other beans as well (nearly 5lbs worth).

This problem started about a week after purchase (it worked fine at first). I then returned the machine for inspection, and the vendor replaced the vibe pump and adjusted the OPV to 9. That worked for about a week, but then the problem returned. I just exchanged the machine for a direct replacement, only to discover the same problem this morning.

This is now my third pump, so the problem must be related to something else (I just don't know what!). Curiously, when I flush the machine, there's no steam/hissing like I would expect from an HX machine, but I have no idea if this is related in any way. I've read varying reports about this brew pressure issue online, but no definitive solution. In nearly every case, the person replaces the pump, which solves the problem temporarily, only to have it return again a week or two later. What is amiss here?

This thread most closely describes the problem I'm experiencing, but I don't know if fiddling with the OPV would solve the issue. Besides, if I open the machine, then I void the warranty. Although, at this point, I'm ready to try just about anything!

Any ideas? Any help would be greatly appreciated!
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z0mbie
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z0mbie
Joined: 26 Sep 2013
Posts: 340
Location: Online
Expertise: I live coffee

Posted Mon May 19, 2014, 11:07am
Subject: Re: Low Brew Pressure (Bezzera BZ10)
 

What does your espresso flow look like when you observe the drop in pressure during the extraction?
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jferreir
Senior Member


Joined: 23 Apr 2014
Posts: 16
Location: Toronto
Expertise: Just starting

Posted Mon May 19, 2014, 1:10pm
Subject: Re: Low Brew Pressure (Bezzera BZ10)
 

z0mbie Said:

What does your espresso flow look like when you observe the drop in pressure during the extraction?

Posted May 19, 2014 link

The shot is fairly thin and watery throughout, regardless of the grind, if that makes sense. There's barely any crema produced. The few times I was able to pull a shot at 12 bars, there was plenty of crema and the shot wasn't nearly as sour. Because the extraction never gets above 8 bars, there's not a huge difference in the espresso flow during the shot.
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z0mbie
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z0mbie
Joined: 26 Sep 2013
Posts: 340
Location: Online
Expertise: I live coffee

Posted Tue May 20, 2014, 6:53am
Subject: Re: Low Brew Pressure (Bezzera BZ10)
 

There is really no way to rule out the grind as a factor for a watery shot, as grind granularity and consistency is what creates flow restriction.

I apologize if I am incorrect in my assessment that you are relatively new at this.   And if you are, here is are two key observations that I'd like you to make and compare against your own results:

1) The flow should take roughly 30 seconds to produce 30 grams of espresso from the moment you start the pump to when you turn it off.
2) The resultant espresso should be smooth and decadent, flowing out like warm honey.

The above observations are expected with a properly functioning pump operating at 9 bars of pressure during the shot.  Assuming your prep is correct, then a weak pump would not be able to produce much shot volume at all in the same amount of time.

However if your prep was poor, your shots could be suffering from severe channeling, or your grind is too coarse an extremely weak (loose) extraction. I recommend you watch some videos of folks pulling shots with their machines.

BTW, what grinder are you using, and what does your grind look like?

Use this site for reference:
http://www.ineedcoffee.com/03/coffeegrind/
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jferreir
Senior Member


Joined: 23 Apr 2014
Posts: 16
Location: Toronto
Expertise: Just starting

Posted Wed May 21, 2014, 9:50am
Subject: Re: Low Brew Pressure (Bezzera BZ10)
 

z0mbie Said:

There is really no way to rule out the grind as a factor for a watery shot, as grind granularity and consistency is what creates flow restriction.

I apologize if I am incorrect in my assessment that you are relatively new at this.   And if you are, here is are two key observations that I'd like you to make and compare against your own results:

1) The flow should take roughly 30 seconds to produce 30 grams of espresso from the moment you start the pump to when you turn it off.
2) The resultant espresso should be smooth and decadent, flowing out like warm honey.

The above observations are expected with a properly functioning pump operating at 9 bars of pressure during the shot.  Assuming your prep is correct, then a weak pump would not be able to produce much shot volume at all in the same amount of time.

However if your prep was poor, your shots could be suffering from severe channeling, or your grind is too coarse an extremely weak (loose) extraction. I recommend you watch some videos of folks pulling shots with their machines.

BTW, what grinder are you using, and what does your grind look like?

Use this site for reference:
http://www.ineedcoffee.com/03/coffeegrind/

Posted May 20, 2014 link

I understand how grind and dose impact extraction, and I'm confident this is not the issue. As I stated previously, adjusting the grind and dose has little effect on the extraction, presumably because there is insufficient brew pressure at the GH. The bar pressure during back-flushing no longer reaches the OPV setting of 12 bars, so I can only assume that the pump is beginning to fail. When I initiate the back-flushing, the pressure steadily increases to about 8 or 9 bar, but then struggles to reach the factory OPV setting of 12 bars. From the time I push the button, it  takes approximately 30 seconds for the needle to reach 12 bars of pressure.

I just returned the machine to the vendor, who is going to replace the pump for the third time. There was a bit of a language barrier with the technician, but I believe he said they received a bad batch of pumps as a few issues have already been reported. I'm waiting on replacement parts to arrive before the repair can be done, but I'll post updates when they become available.

This has been a pretty frustrating experience as the BZ10 hasn't worked correctly for more than a few days after purchase. I'm hoping this will be the final repair, but who knows...
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