Recommendations for pressure setting on OPV requested

[ristrettobrain]

This is a follow on to my previous post. So now, assuming that I figure out how to adjust the OPV on my ECM Giotto Classic, at what pressure do those with more wisdom than I suggest I set the OPV on my machine?

Any experience with various settings will be appreciated.

Thanks in advance,

Mike

[Abe Carmeli]

Set it to 10 bars, if you are using a portafilter mounted pressure gauge with no flow. This translate to 8.75 bars with 60 ml flow (a double) and 9 bars with 50 ml flow (a double Ristretto). So, in your case, set it to 10.

[ristrettobrain (original poster)]

Abe,

Thanks for the advice, I am glad I asked the question . I was getting the idea that 8.5 to 9 bar is a good range but didn't realize the conversion factor to account for flow. But I must ask, why is this? If the puck is offering, say, 8.75 bars of resistance why would it matter if the OPV was set to relieve pressure at some point above that? Say, 9 bar, 10, or 12.5?

On a tangent, I have appreciated your and Jim's M3 grinder reports and photos. The M3 would be represent a massive investment on my budget but as something that would be used often and, hopefully, last decades it may make sense. Therefore ongoing reports will be highly useful, e.g., the belt slippage issue. Issues related to long term durability are important. Lastly, I must add that the shot photos you posted on that thread are spectacular. I must be going off of the espresso deep end because I'm thinking man that's gorgeous, it would make a great poster!

Mike

[HB]

You know you're getting lazy when you resort to quoting yourself:

Keep in mind that the OPV determines the maximum pressure during the extraction; the puck determines the minimum. So the OPV not opening isn't an issue for double espressos since the pump flow rate works out to around 9 bar anyway (as explained earlier in the thread). If you're pulling ristrettos (or "accidental ristrettos" as Jim sometimes calls them), it's another story. Then the OPV determines the maximum pressure by venting excess water back to the tank, thereby reducing the overall pressure.

The short answer is for true doubles, you're right, the OPV setting isn't important since the pump can't muster more than 9 bar at that flow rate. Many are set to around 12 bar from the factory to protect the machine's plumbing, not regulate brew pressure.


(image courtesy of Ulka S.p.A.)

[HB]

On a tangent, I have appreciated your and Jim's M3 grinder reports and photos...

Follow on discussion merged with existing "Bench" thread of the Versalab M3 grinder.

[JonR10]

Shoot - I had intended not to actually join IN the discussion of the M3, but rather to comment ON the discussion. Oh well, it was just an opinion anyway and everyone knows what THOSE are worth...

[HB]

Sorry Jon... give a moderator some new buttons to twirl and they will feel compelled to use them.

[barry]

The short answer is for true doubles, you're right, the OPV setting isn't important since the pump can't muster more than 9 bar at that flow rate. Many are set to around 12 bar from the factory to protect the machine's plumbing, not regulate brew pressure.


(image courtesy of Ulka S.p.A.)

which line are we looking at here?

[HB]

The Ulka website doesn't specifically say what the three lines represent. My guess is the solid line is the median and the dottted lines are the acceptable error limits.

[barry]

okay, then are you guys pulling huge doubles? it looks to me like a "normal" sized double would push in at 10 to 11 bar.