OPV Basics

[Endo]

For any Mini owners (in a sea of Rotary dudes);

If you want to know more about OPVs, this is a "must read":

http://coffeetime.wdfiles.com/local--fi ... _Valve.pdf

The Mini has an OPV like the high quality Izzo/Vivi in this article. Here's a photo of the Mini OPV for comparison (aint she pretty!)

Not sure what the lower o-ring is for though. Maybe at very high pressure settings (non-espresso use), it gets screwed in and provides extra sealing? Makes me wonder if the spring in this industrial baby is too big for light 9 bar pressure settings used in espresso.

Hard to fit a wrench in to adjust, but if you have strong fingers, you might be able to turn it by hand (that's how I adjusted mine anyway).

Mini Vivaldi OPV

s_opv.jpg (68.72 KiB) Viewed 7209 times

[chas]

For any Mini owners (in a sea of Rotary dudes);

Not sure what the lower o-ring is for though. Maybe at very high pressure settings (non-espresso use), it gets screwed in and provides extra sealing? Makes me wonder if the spring in this industrial baby is too big for light 9 bar pressure settings used in espresso.

s_opv.jpg

Good read. Thanks. I think I'll link to it from the VII/Mini site. As to the lower o-ring, this is the same valve using in their rotary machines to dump overpressure into the drip tray where it gets set to ~12.5bar. On those machines the valve will be screwed in further and the lower o-ring gets engaged. Though on my VII, it's still partially visible and not totally up inside the OPV body.

[Endo]

As to the lower o-ring, this is the same valve using in their rotary machines to dump overpressure into the drip tray where it gets set to ~12.5bar.

Ah yes, makes sense.

The vibrating gauge needles have made me wonder how much "damping" is in this OPV system or how hard it would be to build some into it.

If there is a weakness in vibe versus the rotary, I believe it's here.

(Mechanical Engineer and Electrical Engineer....I hope we don't bore everyone to tears).

[chas]

From what little I've heard, the rotary pumps also control their output pressure by feeding water back from the output to the input. This is built right into the pump. Obviously it's a different system than using an OPV with a vibe pump. I wonder if there is an adjustable needle valve or something similar that feeds back a constant amount of water to control the pressure. Such a system would not cause a fluctuating needle which you definitely don't see with a rotary.

[caf4brains]

Commercial positive displacement pumps have something similar to a water-hammer dampner in your home plumbing to damp out pressure pulses, but my recollection of seeing them in the field was that the pressure gauge still oscillated some. I suppose that the bigger the dampner the smaller the oscillations is expected. On my Mini I see the pressure gauge on the pump discharge settles down to almost rock steady when there is a blind basket full of water in place or when I'm seeing a nice steady pour of espresso. Those of you blessed with piping tools my consider installing a tee into the pump discharge line with the alternate outlet of the tee connected to a vertically-oriented, capped-off piece of tubing to act as a dampner.

[Endo]

Commercial positive displacement pumps have something similar to a water-hammer dampner in your home plumbing to damp out pressure pulses, but my recollection of seeing them in the field was that the pressure gauge still oscillated some. I suppose that the bigger the dampner the smaller the oscillations is expected. On my Mini I see the pressure gauge on the pump discharge settles down to almost rock steady when there is a blind basket full of water in place or when I'm seeing a nice steady pour of espresso. Those of you blessed with piping tools my consider installing a tee into the pump discharge line with the alternate outlet of the tee connected to a vertically-oriented, capped-off piece of tubing to act as a dampner.

My brew pressure gauge seems to suggest the p/i chamber dampens it out during ramp-up. Once it maxes out, the pulses come back.

As others have mentioned many times in other forums, people have measured these vibe/opv pulses with all kinds of fancy equipment and the conclusion is always that it is dampened out in a real pour. Still, I'm always a little suspicious. Some people contunue to say they can taste the difference between a vibe and rotary. We may never know.