Often you'll hear the term "saturated group" bandied about, usually in the context of explaining the advantages of dual-boiler designs like La Marzocco's. But a picture is worth a thousand words:


"Gooseneck" extends the grouphead away from the boiler to the service area


Closeup of the grouphead itself; notice the copper water inlet

Thanks go to the folks at Counter Culture Coffee who use this cutaway as part of their barista training course.

malachi wrote:Oh... and I think now folks can see why... I prefer this design to the E61.

For those who joined late in the discussion, below is an excerpt from Lino's E61 Group Espresso Machine: Detailed Interior Schematics:


Cross Section, lever and valves in brew position (courtesy Verna Design Inc., please do not copy)

Comparing the two, you can see that the grouphead and indeed the backside of the La Marzocco dispersion block works as a direct extension of the boiler (hence why they call it "saturated"). In contrast, the E61 relies on circulation tubes leading to/from the boiler to bring water heated by the steam boiler to the grouphead and return cooler water (hence why it's called a "thermosyphon" and forms part of the HX circuit). The low-level details were covered in E61 Group Espresso Machine: Is its reputation justified?

That said, Chris will readily admit the La Marzocco design isn't without its own compromises. Ask him about the flowmeters on the automatics. Go ahead. I dare you.

malachi wrote:would love to figure out a good solution for the 3-way valve location nonsense. if you have a plan...

A quick recap for those following along who aren't familiar with the "valve location nonsense," at least as I understand it.

The multi-group La Marzoccos share a single rotary pump. Brew water is delivered to each diffusion block via a copper tube that momentarily exits the group, at which point a solenoid controls the flow, then re-enters to complete the pathway. Problem is, that little dash outside loses precious heat, and partially explains why barista competitions adamantly insist competitors flush the grouphead (not just to clear the dispersion screen, but also to clear the cooler water from this out-of-boiler portion of the delivery tubing).

For automatics, the situation is worse. A flowmeter works like a water wheel, spinning as the water passes to calculate the volume. There's a separate flowmeter per group, and once again, the brew water takes the long way home to pass by the flowmeter outside the group to reach the diffusion block (a single-group automatic wouldn't have this concern because the flowmeter is installed immediately after the pump, it isn't metering brew-temperature water, and thus doesn't contribute to heat loss). These two design choices earn the ire of those seeking uber-stable brew temperature.

(corrections are welcome)

AndyS wrote:Are you familiar with Paul Pratt's modification?

Very cool. Having only one group to deal with does simplify things though, which makes me wonder: Do any cafes use several well-capable one-group machines instead of a multi-group? Taking one machine offline for maintenance would be a lot easier. Or it is just a question of added space and potential maintenance (i.e., more parts means more potential failures)?