Low Brewing Pressure Bezzera BZ07

by **CurtisHsu** on Sun Sep 18, 2011 10:30 pm

Dear all:

I've tried to screw in the OPV to set the brewing pressure to 10 bar.(Bezzera BZ07 with PID)
During extraction, the pressure gauge raise to 9 bar for 1-2 seconds,
then descend quickly to 5-6 bar and stay there.
Meanwhile, very small amount of espresso was extracted due to the low pressure.

Would someone please kindly advise the possible cause of the problem?
Thank you very much.

Curtis

by **another_jim** on Sun Sep 18, 2011 10:55 pm

Look at the second hose into the tank.

-- If the OPV is malfunctioning, most of the water will be flowing back into the tank. In that case, disassemble the OPV, clean and reassemble. Grit can cause the problem. If that doesn't help; you may need a new OPV.

-- If no water or very little water is flowing back, the pump is not holding pressure. Disassemble and clean it. If that doesn't work, it may need to be replaced.

by **cpreston** on Mon Sep 19, 2011 4:41 pm

I have the same machine, bought a year ago. It had similar symptoms when new, with a drop to around 7-8 bar. The pump turned out to have been defective.

by **CurtisHsu** on Tue Sep 20, 2011 10:09 am

Thanks Jim for your helpful instructions.

I ran the extarction again and found that the pump seems to stop working(or slow down, 'cos the vibratory noise become very very low) while the pressure raises to approx. 8.5-9 bar during extraction.
And consequently the brewing pressure drop down to 5-6 bar.
This time, after stay 5-6 bar for about 5 sec., the pump active and the pressure raise to 9 bar and then drop to 6 bar again.
There's little water flow back to tank during extraction.

Then I replace the portafilter with blind basket.
The brewing pressure raise and stay at the setting value.
The pump slowdown, and little water flow back to the tank.

Thus I remove the pump and disassemble it.
Please see attached picture.

I removed the OPV as well and found it seems to be normal(no clog).
Should I replace the pump with a new one?

by **another_jim** on Tue Sep 20, 2011 10:20 am

The symptoms you describe (very precisely, by the way) are caused by a failing pump. Specifically, in you photograph, the white cylinder can be screwed apart at the right end, and will reveal a metal core and a tiny plastic ball valve and spring. That 1 cent ball valve is deformed, but there are no replacements, either for it or the whole plastic cylinder assembly, so you get to replace the pump.

You can try taking the cylinder apart and immersing the ball valve and the rubber gaskets in citric acid or vinegar. This dissolves any residues and improves their seal. When this happened to me, the fix worked for a few months, a few times in a row. So it might extend the pump life by a few months.

by **CurtisHsu** on Tue Sep 20, 2011 10:32 am

cpreston wrote:I have the same machine, bought a year ago. It had similar symptoms when new, with a drop to around 7-8 bar. The pump turned out to have been defective.

My machine is just six months from new.
Usage about 1-2 cups espresso per day.

My bad-luck friend bought the same brand new machine at the same time,
the machine can not work at all.
And turns out that it comes with one metal tube broken and two wires disconnected.

by **jfrescki** on Tue Sep 20, 2011 11:24 am

CurtisHsu wrote:Then I replace the portafilter with blind basket.
The brewing pressure raise and stay at the setting value.
The pump slowdown, and little water flow back to the tank.

I am the last person who should be getting involved in this conversation, but fortune favors the foolish! Doesn't the above statement indicating the brew pressure remains constant against a blind portafilter suggest he actually just has some awful channeling?

by **CurtisHsu** on Tue Sep 20, 2011 11:46 am

hi Jim,

I will replace the pump with a new one.
Many thanks for your help.

hi jfrescki:

very little espresso was extracted, and I confirm there's no channeling.
please see the first post of this topic.

by **another_jim** on Tue Sep 20, 2011 11:57 am

jfrescki wrote:I am the last person who should be getting involved in this conversation, but fortune favors the foolish! Doesn't the above statement indicating the brew pressure remains constant against a blind portafilter suggest he actually just has some awful channeling?

I had this problem on my Elektra Semi twice. Since the Elektra has no gauge, it was steady pressure against a PF (blind filter) gauge, and odd flow variations during the shot. Finally the pump started making reving noises as the valve got less tight, and I figured out what was happening.

I wonder if there are installation variations that affect pump life. In my Semi, the pumps last about 18 months; they lasted over five years on my earlier machines. But other Semi owners don't report early pump failure. Probably no way of finidng out other than collecting a large number of pump life statistics

by **cpreston** on Tue Sep 20, 2011 3:18 pm

FWIW, my replacement pump is marked "max water temp 25C", or 78F. But I have regularly measured around 100F in the reservoir.

However I'm not sure if the new pump is identical to the original; it was replaced by 1st-line


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