The GS3 paddle version does preinfusion at line pressure. The auto version at pump pressure.

I am trying to understand what is actually happening in the machines and I am unclear about how it works.

When the pump is working during normal extraction, lets say it pressurizes to 8 Bar.

Does the pump start out with water at a lower pressure and then ramps it up or is the 'resting' pressure of the water in the boiler already sitting at 8 bar and the pump's job is just to move the pressurized water out of the boiler and into the group?

I still think you should get the paddle version.
I actually thought there was no pre infusion with the volumetric version. Maybe someone else will chime in.

There is preinfusion on the volumetric version but it's at pump pressure.

That's what prompted the question. The difference between line pressure of 1.5 bar and pump pressure of 8 is bigger than if the starting/resting pump pressure is lower - whatever that is. Does it make a difference? I don't think that issue has been settled really.

I would think opening pump pressure is the same as closing pressure in an extraction (my terms) but I don't know.

I am all for the paddle, I just worry that my other half will gripe. I am not worried about the maintenace. I plan on having you do it.

The water in the coffee boiler is maintained below boiling point, so it is essentially unpressurized. When the pump cuts in, it ramps up the pressure fairly quickly to the 8 or 9 bar set point for brewing.

The paddle opens the valve so that the existing line pressure (usually about 1.5 - 3 bar) flows through and water from the coffee boiler pre-infuses the basket.

If the MP is not plumbed in, then there is no line pressure available, and if you open the valve to the PI position, a slow dribble ("pre-delusion") escapes through the group. I can assure you that this does NOT help the shot - after months of experimentation I was never able to make this pre-wetting work: it does not saturate the puck evenly which leads to all sorts of spritzes and channeling.

So in the volumetric version, if it starts the pump running to preinfuse - that doesnt make much sense to call it preinfusion - isnt that the same thing as starting the extraction? Or does it let the water flow into the group at some lower pressure without running the actual pump?

That's the crux of it and what I am not understanding.

From my (limited) understanding of the Volumetric GS/3 - there is a bypass valve that stays open for a programmed amount of time. This is the p/i and the pressure is very low, but the puck is still getting wet (probably not saturated though). *don't take that to the bank - i could be off base.

The MP model will pre-infuse at about 1 bar when not plumbed in. Lot's of debate on what pressure is suitable for p/i, but most are comfortable with about 3 bar. The MP will infuse at line pressure when plumbed in, and if you use a regulator on the water supply; you can set the p.i accordingly.

In my experience, p.i can make a pretty big difference in the cup. I really like using it on the front and back end of a shot when using a bright coffee. It helps attenuate some of the acidic peaks while retaining the terroir of a coffee. I believe this is (in part) due to the finer grind required when utilizing p/i. Naturally, not all coffee respond positively to p/i in a general sense. Some coffees do really well when you put the screws to em' right off the bat.

On a lesser important note, there is added "forgiveness" when using p/i. I use that term loosely. It seems that puck prep. deficiencies are not as pronounced when the shots is pre-infused.

Thanks, Jammin.

This is interesting and I will call Chris' and ask for clarification.

My line pressure (and I am plumbed in) for the Vivaldi 2 is 1.5 Bar. Knowing what the volumetric p/i pressure is would be a nice piece of info.

Not really on the subject of characteristics of GS3 models, but:

The Breville BES900XL is a reservoir-only espresso maker that offers a "pre-infusion" setting. The vibratory pump is operated at partial power (default is "60%") to saturate the puck with water at less than full infusion pressure. On my machine, this works out to about 3 bar. The pre-infusion power setting is programmable -- I have not experimented to see if it can be reliable set to a pressure as low as 1.5 bar; but if that's possible, one should be able to compare coffees pre-infused at different pressures. (The pre-infusion time is also programmable.)

As far as I know, it's not possible to go back to pre-infusion pressure at the end of a shot as I've seen done with many pressure-profiling systems.

I've read opinions that "pump pre-infusion" is not the same as line pressure pre-infusion. If the pressures are the same, would that still be true? (pulsation in the flow from a vibe pump v. smooth flow from hydrostatic line pressure?)

I spoke to someone at Chris Coffee and here is the deal.

The volumetric version preinfuses at your line pressure - no more no less.

The paddle version allows you to surf/dial pressure anywhereup to your line pressure.

So the benefit is being able to get more gentle (or progressive) p/i with the paddle. You are not getting huge pressures with the volumetric version.

If you want to change your line pressure, you can change the p/i pressure (volumetric) or max pressure (paddle).

I hope this information helps anyone who might be deciding between the two versions.

Evan

I don't believe the paddle offers so much control. And I remember using a GS/3 volumetric that had only an on/off delay to give a "pre-infusion". I don't know if they have changed the software recently, as in fact it would be easy to open the 3-way valve and let the water pressure do the pre-infusion before the pump enters.