I noticed the test Lusso is one of the "newer" versions. There are some changes that have showed up in the Lussos in the past few months, most noticably: the pressure gauge is different, there is more play in the lever and the plastic shield protecting the interior wiring and pressurestat is smaller for easier removal. I am wondering if there are any further differences that might skew the results between the two machines, ie. pre vs. post Millennum La Pavonis. Several contributors to this thread are comparing your Lusso results to their Lusso results.

Fullsack wrote:I noticed the test Lusso is one of the "newer" versions. There are some changes that have showed up in the Lussos in the past few months, most notably: the pressure gauge is different, there is more play in the lever and the plastic shield protecting the interior wiring and pressurestat is smaller for easier removal. I am wondering if there are any other differences that might skew the results between the two machines, ie. pre vs. post Millennum La Pavonis. Several contributors to this thread are comparing your Lusso results to their Lusso results.

If the group comes to temperature without a purging flush on the newer Lussos, I suspect the vapor-lock issue in the thermosyphon has been addressed.

Regards
Timo

HB wrote:Just another day at the office....

In this picture of the latte art foreground, Lusso main left flanked by grinders on the right, what is the pressure-gauge reading?

timo888 wrote:...what is the pressure-gauge reading?

Around 1.0 bar.

HB wrote:Greg Scace, creator of the famous thermofilter, plans to machine one specifically for the Lusso. Once it's done, we will create plots of the Lusso's pressure profile with it. I expect it to look like this:

<image>
From Olympia Cremina 2002: The evolution of design

Though I'm not sure about the height of the peaks. The piston is much smaller than the Microcasa, but the spring seems to pack about the same punch. It should put out more brew pressure. I'm not willing to pop THAT spring out of the group, the end isn't a bolt-in like the Microcasa! I'll have to ask Jim if he minds me tapping a hole in the side of the Microcasa's group to plot the brew pressure. I've always wanted to do that...

The PV's group design does not allow for the exchange of water above and below the piston, like the Elektra and Cremina groups do. I don't really understand how the flow of water above and below the piston works in conjunction with the flow of water from the boiler on the MCaL and Cremina groups, but I do know that with the PV group, there must actually be negative pressure at the group on the (piston's) upstroke, so I would imagine zero would not be the bottom point on the actual pressure graph. What makes this interesting to me is that the way you make the second pull will affect the shape of the valley - for example, two short strokes that minimize the travel of the piston beyond the boiler fill hole in the group versus two strokes that allow the piston to travel its full range. In the first case, I would imagine that the puck would be disturbed less by the shorter duration of the negative pressure.

Does the water exchange between the top and bottom of the piston change the duration of the negative pressure in the MCaL and Cremina groups, or are all three of these groups similar in the way the upstroke creates negative pressure?

Dogshot wrote:The PV's group design does not allow for the exchange of water above and below the piston, like the Elektra and Cremina groups do...

Does the water exchange between the top and bottom of the piston change the duration of the negative pressure in the MCaL and Cremina groups, or are all three of these groups similar in the way the upstroke creates negative pressure?

Correction: The Lusso and the Microcasa don't have water above the piston; instead they have a "breather" hole like on a bicycle pump to allow air above the piston to escape during the upstroke. Cover this hole on the backside of the grouphead and you can feel it push out air as you press down the lever. I assume all of these levers produce some negative pressure on the upstroke, though the newer Cremina does have fancy gasket that "jellyfishes" on the downstroke. Steve looks at the older design in Restoration of an Olympia Cremina:


The "old" Cremina piston face and the mystery holes

And the newer design in Olympia Cremina 2002: The evolution of design:


The "new" Cremina piston gasket and no more mystery holes

I don't know if the purpose of the holes/jellyfish gasket is only for less friction and therefore a smoother upstroke as Steve noted, or if it also measurably reduces the negative pressure.

HB wrote:Correction: The Lusso and the Microcasa don't have water above the piston; instead they have a "breather" hole like on a bicycle pump to allow air above the piston to escape during the upstroke.

There's an old thread that has a photo of the inside of the MCaL's group, which clearly shows 3 holes - one very near each end of the group, and one that is more central. I can guess that the more central hole is the boiler fill hole, but if the MCaL does not have water above and below, what is the purpose of the other 2 holes?

Dogshot wrote:There's an old thread that has a photo of the inside of the MCaL's group, which clearly shows 3 holes

Sorry, I know the photo you're referring to and it's of my Microcasa (Steve borrowed it for the Elektra/Pavoni side-by-side). There's only two holes. You had me going for a minute... I just removed the piston and rechecked. There's still only two holes.

The Gaggia Achille does have water above the piston. The water above the piston moves through a one way valve in the shaft/piston on the upstroke. On the down stroke the one way in the piston closes. On the down stroke a negative pressure is created above the piston which opens another one way valve in the heat exchanger and allows water to flow into the piston chamber above the group.

More on that in the Buyer's Guide to the Gaggia Achille.

HB wrote:Sorry, I know the photo you're referring to and it's of my Microcasa (Steve borrowed it for the Elektra/Pavoni side-by-side). There's only two holes. You had me going for a minute... I just removed the piston and rechecked. There's still only two holes.

Dan, thank-you for straightening me out on the MCaL group. About all I can offer in my own defence is the photo about which we are talking:





Whatever it is just above the screen at around the 1 o'clock position looks like a hole. It must be something else. I'm actually pleased to hear how similar the PV and MCaL groups are.

Dave, thanks for clarifying the valve on the Gaggia. The Cremina, however, does exchange water, but does not have a 1-way valve...is that right?