Is it really necessary to adjust vibe pump brew pressure?

by **Ozark_61** on Fri Aug 10, 2007 10:06 am

If the Italians use 14gm for a typical double, and we tend to use 18gm for a double - does this have a correlation to why many report they like to set their machines to 9 bar while most machines come to us set at 11 bar ? ie - does a 11 bar brew pressure do a better job pulling a good shot of 14gm than 9 bar?

Geoff

by **another_jim** on Fri Aug 10, 2007 11:26 am

Ozark_61 wrote:If the Italians use 14gm for a typical double, and we tend to use 18gm for a double - does this have a correlation to why many report they like to set their machines to 9 bar while most machines come to us set at 11 bar ? ie - does a 11 bar brew pressure do a better job pulling a good shot of 14gm than 9 bar?

There's actually no real difference in practices here. Both the US cafe and the Italian industry standard is 8 to 9 bar for rotaries and 11 bar for vibes, measured on a no-flow PF gauge. Given the extra slop in a lot of OPVs on vibe pumps, this will produce around the same flow pressure for both setups. If one is adjusting multiple pumps and machines, it's probably better to have a system that can measure at espresso flow, since there is apparently a lot of variation.

by **Ozark_61** on Fri Aug 10, 2007 1:32 pm

Interesting - It seems that many people are turning their opv's down for 9 bar - but since I have a vibe pump on my giotto and it's 11 bar, should I bother?

by **TimEggers** on Fri Aug 10, 2007 2:04 pm

I really like mine even lower closer to 8 bar. I think we're venturing back into "personal preference" territory on this one.

by **cafeIKE** on Fri Aug 10, 2007 2:34 pm

Ozark_61 wrote:Interesting - It seems that many people are turning their opv's down for 9 bar - but since I have a vibe pump on my giotto and it's 11 bar, should I bother?

11 bar where?
On the gauge or on the puck?
If on the gauge, it's probably about 9.75 on the puck.

The final arbiter is taste. Turn it down. If you like it, great. If not turn it back or higher.

by **TimEggers** on Fri Aug 10, 2007 2:41 pm

cafeIKE wrote:11 bar where?
On the gauge or on the puck?
If on the gauge, it's probably about 9.75 on the puck.

The final arbiter is taste. Turn it down. If you like it, great. If not turn it back or higher.

A very good point, the gage is most likely not indicative of what the puck is actually seeing. My tastes say that 8-bar on my Anita is just right for delicious espresso. I don't worry about what the gage says beyond being a reference point because my tongue says its just right.

I'm curious as to what makes the "dash board" gages so misleading? Their placement in the pressure system?

by HB on Fri Aug 10, 2007 2:57 pm

TimEggers wrote:I'm curious as to what makes the "dash board" gages so misleading? Their placement in the pressure system?

The reading from the onboard gauge and actual puck pressure should not deviate during an extraction (*).

The problem is the over-pressure valve doesn't necessarily perform the same in flow versus no flow circumstances (OPV is nothing more than a valve and spring). For example, the OPV vents all the water when there's a blind basket and only a small trickle during a real extraction. The resistance of full flow through the exit tube is enough to perturb the reading (try pinching the exit tubing to see what I mean). It takes a very small flow to even everything out; when in a hurry without a thermofilter, I've locked in a portafilter pressure gauge with water dripping from an iffy seal. That's enough to eliminate OPV induced error for most machines. OPVs with smaller / stiffer springs are more touchy, I guess because spring resistance is non-linear (mechanical engineers are welcome to correct me).

(*) EDIT: I received a friendly offline correction:

See the last post in this thread Water flow rate - any research on effects? It doesn't include the numbers for a 0.70 mm gicleur which is the size in all of the Quickmill machines (at least the hx ones). A 0.70 mm gicleur produces a calculated delta P of 0.50 bar under the flow conditions in the post.

For numbers on a machine in operation, see Digital Pressure Adapter. Also, a typical spring's resistance is linearly proportional to its compression or extension - the so called spring constant, "k" (pounds/inch). In contrast, a typical automotive strut spring (today) is progressively wound wherein the coil spacing is not uniform and thus the "k" value increases with the amount of compression. In this case, the resistance would be non-linear.

by **Ozark_61** on Fri Aug 10, 2007 6:40 pm

cafeIKE wrote:11 bar where?
On the gauge or on the puck? If on the gauge, it's probably about 9.75 on the puck.
The final arbiter is taste. Turn it down. If you like it, great. If not turn it back or higher.

Dan - sorry if this is getting too OT - feel free to split if needed.

Sure - but trying to avoid taking the panels off the side of my giotto yet again - they are bit of a pain, if unnecessary. Jim had mentioned checking the OPV flow as 2.5 oz IIRC in 25 sec. I pulled the line from my reservoir and am only returning 1.5 oz in 25 sec with the gauge in the pf (effectively a blind basket). Since many reported better tasting espresso at 9 bar (PF gauge or teed off of the opv), I was willing to give it a shot (ha).

by **cafeIKE** on Fri Aug 10, 2007 7:04 pm

Ozark_61 wrote:Dan - sorry if this is getting too OT - feel free to split if needed.

Sure - but trying to avoid taking the panels off the side of my giotto yet again - they are bit of a pain, if unnecessary. Jim had mentioned checking the OPV flow as 2.5 oz IIRC in 25 sec. I pulled the line from my reservoir and am only returning 1.5 oz in 25 sec with the gauge in the pf (effectively a blind basket). Since many reported better tasting espresso at 9 bar (PF gauge or teed off of the opv), I was willing to give it a shot (ha).

1.5oz in 25 sec is ~105ml/minute. Do you start measuring after the pressure has reached 11bar?

An Ulka E5 pumps that much at ~12.5bar.
http://www.ulka.it/eng/e5_gra.htm

It appears you are using a PF gauge. If it reads 11, then that could be ~12.5 on the pump side, matching the Ulka flow.

I assisted a pal with his Giotto which was 8.75 on an actual puck and it made damn fine espresso.
See Digital Pressure Adapter. After I rebuilt the OPV on the Vibiemme, I set the pressure +.25bar higher.

I know what you mean about the panels. Nice clean look, but WottaPITA!

BTW, when was the last descale?

by HB on Fri Aug 10, 2007 8:39 pm

Ozark_61 wrote:Dan - sorry if this is getting too OT - feel free to split if needed.

Good idea, split from Basket Overdosing; time for a serious re-evaluation! Feel free to change the topic title.

another_jim wrote:There's actually no real difference in practices here. Both the US cafe and the Italian industry standard is 8 to 9 bar for rotaries and 11 bar for vibes, measured on a no-flow PF gauge. Given the extra slop in a lot of OPVs on vibe pumps, this will produce around the same flow pressure for both setups. If one is adjusting multiple pumps and machines, it's probably better to have a system that can measure at espresso flow, since there is apparently a lot of variation.

I've not seen huge variations in vibe pump dead head versus flow rate pressures. From what I've measured, it's typically 0.25 to 0.5 bar, though Greg Scace reports measuring larger differences. If an evaluation espresso machine doesn't have an onboard brew pressure gauge, I add a temporary one as shown below. Otherwise I adjust the dead head pressure to 9.0 or flow rate brew pressure to 8.5 and adjust by taste / extraction quality from there.

Giotto Premium

Cimbali Junior DT1

FWIW, Chris' Coffee technicians adjust their outgoing espresso machine brew pressure to 10 bar no flow. But for the barista who cannot have enough tools, there's the new Scace II themofilter:


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