9 bar or 11 bar?

[Endo]

Check out this crazy video from Luca Bezzera explaining why vibe pumps should be set to 11 bar and rotary pumps to 9 bar.

http://www.youtube.com/watch?v=E4y4-E2aL3U

Is it just me, or does he make no sense what so ever? "This pump is small...so it needs 11. This is big (he points to the motor even), so it needs 9".

[chas]

That's just crazy talk. If a vibe pump can keep up the desired flow at 9 bar you don't need any more pressure. Going to 11 bar would make you grind finer to compensate.

[slo]

If a vibe pump can keep up the desired flow at 9 bar you don't need any more pressure.

That might just be it. Maybe their pump cannot provide the proper flow when set at 9 bar but can when set at 11 bar.
Nonetheless showing the pump and talking about the size of it as a reason is just ignorance or a total lack of skills to explain the actual reason(s).

[Endo]

Looks like a regular ulka vibe pump. That means 250 cc/min at 9 bar.

My guess is they are measuring pressure close to the pump source and not at the group head where it is typically a bar or 2 lower. They should simply be measuring it there rather than trying to invent some kind of psuedo science explanation. They lose a lot of cred that way, especially when it comes from someone from the family that invented the espresso machine.

[jbb]

Check out this crazy video from Luca Bezzera explaining why vibe pumps should be set to 11 bar and rotary pumps to 9 bar.

http://www.youtube.com/watch?v=E4y4-E2aL3U

Is it just me, or does he make no sense what so ever? "This pump is small...so it needs 11. This is big (he points to the motor even), so it needs 9".

Well, it is complicated, but maybe this will help explain.

http://www.youtube.com/watch?v=ll7rWiY5obI

[chas]

Looks like a regular ulka vibe pump. That means 250 cc/min at 9 bar.

My guess is they are measuring pressure close to the pump source and not at the group head where it is typically a bar or 2 lower. They should simply be measuring it there rather than trying to invent some kind of psuedo science explanation. They lose a lot of cred that way, especially when it comes from someone from the family that invented the espresso machine.

Any espresso machine when measured both at the pump and at the group head will exhibit a pressure drop. While the pump type and design may enter into this equation, it seems to be related more to the amount of pipe between the pump and the head, the diameter of the pipe/tubing, and the number of passive or active valves in the water path. All of those elements introduce resistance to the water flow.

My GS/3 is a rotary pump machine and I see a sizable drop between the internal gauge and the PF using a Scace device. If I set the PF pressure to 8.75 bar with the Scace, the internal gauge is just above 10 bar. When I first noticed this and before I had thought it through, I thought that either the internal gauge or the Scace were out of calibration. So I did a test. I unscrewed the cap with the hole that water flows out of from the Scace device and temporarily plugged the hole. This effectively let me check the water pressure at the PF as if I was using a blind basket. According to the laws of fluid dynamics if there is pressure but no flow in a pipe, the pressure will be the same everywhere along the length of the pipe. Sure enough the Scace device exactly matched the internal gauge with the pump on and no water flowing through the system.

BTW: The above also proves that if you want to build your own PF pressure gauge to measure the real PF pressure when pulling a shot, it must emulate the water flow while pulling a shot. The Scace passes about 2oz of water in 30 seconds. On the other hand if you have an older machine that has no internal group pressure gauge like the orignal S1, you can always block the water flow in the PF pressure device in order to test the actual pressure being output at the pump.

[Endo]

You are right of course.

It's still strange why Bezzera claims the pressure loss is greater on their smaller machines. I would think the pressure drop in the flow path on all their machines would be very similar (or at least within 1 bar).

My guess is most of the smaller Bezzera machine owners just don't realize the factory is over-pressurizing their home machines. If anything, they probably just figure more is better. Just like on the Nespresso machine boxes...."powerful 15 bar pump!"

[JohnB]

Bezzera is setting the vibe pump MAX pressure to 11 bar. What pressure you are going to see at the puck will depend on the grind you are using for the particular dose although it can't exceed the OPV max pressure setting.

From: http://www.home-barista.com/espresso-gu ... hines.html

"Unlike rotary pumps, vibratory pumps produce a pressure that is strongly inverse to the rate of flow. If there are no controls, one must make a 2 ounce in 20 to 25 seconds espresso to get the pressure inside the 8 to 10 bar range. Smaller, slower pouring shots will have far higher pressures; larger, faster pouring shots will have far lower pressures. Better home machines have overpressure valves to limit the maximum pressure to about 10 bar, so that single and ristretto (reduced) espressos can be made without exceeding the normal extraction pressure range. Long shots, like Swiss café crema, will brew at 4 to 6 bar, no matter how well the vibe pump is controlled."

I have the max pressure set to about 11.5B on my Strega as I want to achieve a full 11 bar pre infusion before switching to the lever with no pressure bleeding off through the OPV drain. Even though the OPV is set to 11.5b the actual pressure at the puck might only be 8/9/10 bar if I didn't grind fine enough.

[Endo]

I assume everyone knows we are only discussing MAX pressure when referring to OPVs. (After all, that IS its only possible function).

Just curious, why would you ever consider pre-infusing at shot pressures or even higher? Is this something new that people are experimenting with?

[JohnB]

It's all in here: http://www.home-barista.com/reviews/bez ... 18933.html as far as the 11b p/i goes. Works very well with the lever to bring out exceptional shots especially with coffees or roast levels you might not normally use for espresso..

Concerning the video; what's the big deal? He's simply pointing out that a commercial rotary & a vibe pump require different settings as they function differently. Hardly earth shaking news. You wouldn't set the opv on your Mini so max pressure was 9 bar would you? 10b seems to be the minimum from the factory setting which is commonly 11b.

[Endo]

You wouldn't set the opv on your Mini so max pressure was 9 bar would you?

Yes. 9 bar is exactly what mine is currently set to.

But keep in mind, I measure the pressure using the most accurate method, a gauge attached to PF and with a flow simulating the brewing flowrate (like on the Scace 2).

I suspect the confusion may arise if the gauge on the Bezzeras (on the front of the machine) are either located too far upstream of the PF or perhaps more likely, they are simply measuring the non-flowing static pressure (as mentioned earlier by Chas). Either way, the same would happen regardless of the pump type used.

[JohnB]

I don't think there is any confusion on Bezzera's part. Having the max pressure set to 11 bar doesn't prevent you from pulling a shot at 9 bar but having the pressure maxed out at 9 bar would certainly limit your options with a vibe pump.

[Endo]

Have you tried pulling a shot less than the max OPV setting (i.e controlling backpressure via the coffee)? It's an almost impossible task. No matter how good your grinder is, if you set it at 11 and aim for 9 bar, I can assure you you'll end up up with a totally random 2 to 8 bar gusher 9 times of of 10.

On the other hand, with a direct lever, you can easily control minute pressure changes at the source. That's the beauty of our Creminas.

By the way, I never asked you....what do you think of your Cremina compared to all you other machines?

[JohnB]

By the way, I never asked you....what do you think of your Cremina compared to all you other machines?

I like it but I also like the Strega. As with most of these levers I think there is too much Kool-Aid drinking going on. They are both capable of producing a very nice shot if you get everything right. Pulled a couple shots of Blue Jaguar with the Cremina today. One was really nice, the second merely ok. Neither approached what I effortlessly get from the Speedster.

I installed the teflon group seal that comes with the Olympia factory group kit in place of the old style 67 seal. The machine will idle all day at 178*F measured at the right rear bottom of the group just above the bell. Takes longer to warm up but a few half pumps will bring it up to 185*F quickly.

[Endo]

The Cremina is a challenge to get consistency. But I must say I am one of those caught up in the cult-like power this small and simple machine has over its owners.

Still, like the Pharos grinder, it's not the machine I'd choose as my daily work-horse. For that, the Vivaldi and Vario are hard to beat.