OPV not working correctly??

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

#1: Post by BaristaMcBob »

My machine is a Bezzera BZ10. The reservoir has three white silicone tubes. One feeds the pump. The other two smaller tubes come together in a Y-connector and dump back into the reservoir.

With a blind basket, the pressure gauge shows 12 bar. I expected water from the OPV to feed back into the reservoir, but actually, no water feeds back.

Is this normal?

ira
Team HB

#2: Post by ira »

Sounds like the OPV is set wrong or stuck. Can it be adjusted and have you tried adjusting it?

BaristaMcBob (original poster)

#3: Post by BaristaMcBob (original poster) »

A while ago I opened it slightly to set the max brew pressure to 11 bar. It's not one of those newer adjustable OPVs. But I was able to reduce the max pressure. That helped eliminate random channeling.

Is this something I can disassemble and check for scale?

JRising
Team HB

#4: Post by JRising »

But what happens at 12Bar? Does the pump stall, or does the water go somewhere else?
While it can still brew perfectly well even if it's pump is unable to exceed 12 bar backpressure, an Ulka EP5 (or whichever Bezzera uses) should be able to exceed 12 Bar. If it is stalling, you'll want to replace your pump soon.
If the water is going somewhere else, you'll need to find out where.

Lastly: If it really does have a single, non-adjustable OPV working as both its expansion valve and brew circuit pressure limit, you may want to consider replacing it with an adjustable. 12 Bar is fine for an expansion valve so long as the machine has another OPV or a good pump with which to set brew pressure.

BaristaMcBob (original poster)

#5: Post by BaristaMcBob (original poster) »

At 12 bar (blind basket), I can hear the pump continue to vibrate at a quieter sound. No water flows back to the reservoir.

The BZ10 has two pressure relieve valves, hence the two silicone tubes running back to the water tank. One valve is right after the pump. The other is the so-called "OPV" valve which seems to be connected to the 3-way solenoid.

Yes, I used to brew espresso at the full 12-13 bar without problems, except for channeling. That's why I adjusted the "OPV" slightly.

I also notice that sometimes the brew pressure gauge osciliates slowly between 7 and 11 as if the OPV is confused.

JRising
Team HB

#6: Post by JRising »

Oh, okay. So the one right at the pump is to set the maximum pressure to which the pump can raise the brew circuit. Set that one to your 8.5 or so. If you're getting 12 bar against a blind basket, this is the one to clean and set.


The one located between the brew circuit's check valve and the brew valve is the expansion OPV, it prevents the plumbing from exploding due to the pressure created by thermal expansion of the brew-circuit's water caused by the element heating it. That one is fine at 12 or wherever.

Coffcarl

#7: Post by Coffcarl »

The bz 10 parts diagram does not show an opv at the pump (my bz99 has one). If he did, this is where he would want to adjust it, and the other one in the path would function as a safety at 12 bar.

My OPV at the pump returns water through a short hose to the pump intake.

Instead, the first one in in the water path shows as adjustable 9-12 bars, and the OP should adjust that accordingly. He may need washers or plumber's tape to prevent a leak there if he backs it off. The second one shows as a nylon part, and I am not sure what that is. It could have a weakly sprung stop valve that allows for a smooth buildup of pressure to help with preinfusion. My bz99 has a weighted valve for that purpose in that place.

At any rate, the OP should see water returning to the tank through the first hose at the OPV set point, and (if my assunption is correct) a small amount of water returning to the tank from the second hose for a few seconds before pressure builds up in the grouphead.

cafe102

#8: Post by cafe102 »

Check to make sure the tube out of the OPV didn't kink when you adjusted it. The tube is very soft and can easily be "un kinked" by twisting it right on the nipple. Don't ask how it know this :oops:

Coffcarl

#9: Post by Coffcarl »

Can you post a picture of the valve at the pump?

Thanks

BaristaMcBob (original poster)

#10: Post by BaristaMcBob (original poster) »

I get what you're saying, but perhaps you have the two valves mixed up? All the youtube vids describe tinkering with the one by the solenoid to change the max brew pressure. The other valve, near the pump, has no information about any adjustments.