Bezzera BZ07 Brew Pressure Problems

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
Tio Tom

#1: Post by Tio Tom »

I am working on a Bezzera BZ07 DE that I purchased used for a friend. It is a beautiful little machine but it is giving me some major headaches. Primarily, I am having a difficult time achieving proper brew pressure. I found and examined the in-line orifice [spec. sheet says 1.2mm dia] which is located in a elbow fitting right at the three-way valve. [See attached diagram] To me the opening seems too large. My experience has been that regardless of whether or not a portafilter with coffee is locked into the group, the machine should produce the needed 9/10 bar pressure for extraction because of the resistance produced by the orifice. This machine does not register any pressure on the gauge until either the full portafilter or a blank disk is engaged. I have made several attempts to adjust my grind setting and tamp but I can only see 9 bar of pressure when it it chocked tight. For a normal looking extraction it only hits about 7 bar. When I put a blank disk in the head, it goes right up to about 10 bar. I would appreciate any comments on this situation. I am hopeful that I can turn over a great running machine. Thanks.



Flitzgordon

#2: Post by Flitzgordon »

The Bezzera and many Italian espresso machines with vibration pumps are designed for at least 11 bars.
If you are getting 10 bars with the blind, then that's the maximum it can reach and should be extracting.
Having 7 bars of pressure, it's probably because the extraction is too fast and is not holding up.
How much are you getting in 20 seconds? It should be about 50ml or less.
I think you will need to make much finer grind adjustments and/or use more coffee to get the right resistance.

The pressure is controlled by the OPV, not this orifice

User avatar
Jeff
Team HB

#3: Post by Jeff »

It is possible that the pump is getting weak, but I can't really diagnose that with the information so far.

The typical E5-series Ulka pumps can produce around 15 bar of pressure with zero flow, about 240 cc/min against a typical 9-bar back pressure (some Bezzera machines are set at 11 bar, from what I've read), and around 600 cc/min with no restrictions.

The gicleur you're referring to is not to generate pressure for extraction, but to limit the inrush of water into the basket during the early phases to a reasonable level.

The puck and basket's "resistance" is what causes the pressure rise you see for extraction. When it hits the OPV valve's limit, then the excess is dumped, usually back to the reservoir.

One test that might help would be to measure the flow out of the OPV relief tube when you've got a blind basket in place. That way there's load on the pump comparable to pulling a shot. 240 cc/min is roughly what I'd expect from a healthy pump (at around 9 bar). If it is significantly less than that, I'd consider replacing the pump.

As you can see from that spec sheet, the different Wattages aren't any different in how they pump water. What is different is the duty cycle -- A pump with a 2/1 duty cycle is perhaps a bit more robust than one with a 1/1.5 duty cycle. As I recall, these are spec-ed with 20°C water in a 25°C environment, which is a lot more benign than the inside of the espresso machines I've known.