Low Brewing Pressure Bezzera BZ07 - Page 2

http://users.rcn.com/erics/ · by **erics** on Thu Sep 22, 2011 12:09 am

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

Real nice pic . . . BUT I sure hope you didn't lose the small plastic ball and spring that should have come out of the discharge housing (brass on right). That plastic ball and spring are a suction check valve assembly. It is VERY EASY (even with some precaution) to drop the ball into "never-never land". A sticking suction check valve will cause the same symptoms you are experiencing as will an intermittently defective thermal fuse which is fitted into an external pocket on the pump housing.

If you can find it, I would appreciate it if you could measure the diameter of the plastic/glass(?) ball - shown in red. If you remove the 90 ell from the right end, the brass part comes out and the end where the 90 ell was screwed in contains a discharge check valve that Jim was speaking about. The plastic cage sorta screws out with small needle nose pliers.

by **another_jim** on Thu Sep 22, 2011 1:05 am

Yeah, that's the ball I was talking about. Once it (or the seals?) deforms , the pump may not hold pressure. I couldn't figure out any way to repair it. If you know how ...

by **CurtisHsu** on Fri Sep 23, 2011 12:37 pm

Thanks erics for the pump drawing.

The red ball you refered is a plastic ball(white one in the pic). Please see attached picture below.

I assemble the pump back before read your reply.
The grid on cutting mate is 10mm x 10mm, thus the ball is estimated to be 3-4 mm in diameter.
The shape is not deformed and I thought the problem may not caused by pump.

While re-check the pressured water route of grouphead,
I found a screw(to fix the solenoid body of 3-way valve, refer to white arrow in pic below) is loosen,
and lead to the solenoid body(the black box in pic below) can play/migrate about 2mm.

To my surprise, brew pressure is normal after subject screw is fastened.

The root cause(I guess) to explain this symptom is:
The solenoid can not provide sufficient force to 3-way valve due to position migrated.
and cause the pressure leaking(the solenoid is energized during extraction).
- during extration, the leaking(3-way valve + coffee bed) is more than pump capability.
- when using blind basket, the pressure can be held due to the pump capability is more than the 3-way volve leaking.

Sample of 3-way valve drawing

by **another_jim** on Fri Sep 23, 2011 6:29 pm

Three way valve not holding pressure -- a logical possibility I never thought of -- good catch.

by **Lyvyoo** on Tue Nov 01, 2011 7:23 pm

A tip for the OPV mod:

I read to the forums that it must set the opv at 9.5bar with the blind filter, in order to obtain 9bar with the coffee. My BZ10, at 9.5-10bar with blind filter, go to 8 bar with coffee. So the final setting was 10.5 bar with blind filter, for 9bar with coffee.

by **CurtisHsu** on Wed Nov 09, 2011 12:22 am

It turns out the the loosen screw on 3-way valve is not the root cause.
The brewing pressure still unstable after the 3-way valve was tightly installed.

The root cause is over screwed of OPV. I unscrew the OPV for 2-3 turns.
The brewing pressure is stable and adjustable now.

I believe the problem has same symptoms with below post,
Pump? OPV? Check Valves? Wit's end!


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