Primacog wrote:I assume you are referring to single group spring levers that home enthusiasts would be interested in.

Those classifications you have proposed seem to me to be ways in which an espresso machine's temperature is regulated or controlled (or not) and as daveyb mentioned, are not specific to lever machines but can be applicable to pump machines as well. Thus they wouldn't be as useful as a means to classify different types of spring levers in my opinion.

It seems to me that one useful way to differentiate between different kinds of home spring levers can be to divide them into traditional non-grouphead temperature and/or preinfusion pressure adjustable designs, and on the other hand, more contemporary grouphead temperature adjustable and/or preinfusion adjustable designs. Those parameters enable the machines to be able to be adjusted more easily to suit lighter roasts.

Within the first category are the vast majority of spring levers such as vintage levers and such modern machines as izzo pompei and Alex, profited pro 800 (its PID can only control the temperature of the boiler and not the grouphead directly and separately) etc.

In the second category can be divided into two sub categories- the first where only the preinfusion pressure can be directly manipulated and the second where both the preinfusion pressure and the grouphead temperature xan be independently manipulated. As far as i can recall, the Londinium R24 may be the only representative of the first subcategory thta I am aware of, while the second sub category has the LM LEVA X single group machine, the acs vesuvius evo, and the Nurri L-type SA Machine. There is also an upcoming commercial oriented machine from acs called the vostok that will also be available in single group format. While the LM LEVA X controls the grouphead temp through having a saturated grouphead, both the vesuvius evo (and vostok) and the Nurri use cartridge heaters to independently heat up the grouphead which can be controlled through the PID. The vesuvius evo uses a gear pump to control the preinfusion pressure while the nurri uses a rotary pump to do so.

RistrettoCapp wrote:
Now that I'm understanding SOME of the lever group types and the various implementations, this is where my head logically goes.. which implementation, or modification of implementation, provides the most stable/adjustable temp ranges.