As you can see by the diagram below. There is a lower port that allows water into the area below the piston, when the piston is in the up postion. This makes sense. Then above the piston there is a second inlet for water that looks like it allows water into the area above, the piston. I'm having a hard time reconciling that in my head.

Does it even out the pressure?

Wouldn't it make it harder to move the piston to the up position, fighting against both the tank pressure and the spring. Wouldn't that mean you need to have seals up and down, on the piston, and seals on the shaft to the lever?

It seems like there must be some gain from doing it with all the extra parts needed to make it work, so I'm wondering why?

deathguppie wrote:It seems like there must be some gain from doing it with all the extra parts needed to make it work, so I'm wondering why?

That's a diagram of a manual lever (Olympia Cremina), not a spring lever. The extra port allows you to draw water into the space above the piston from the boiler, thereby warming the brewhead very quickly. Steve Robinson (leader of the LMWDP) showed me this lever-up/down trick for tweaking the resultant brew temperature. Not all levers will have an extra port, e.g., the Ponte Vecchio Lusso has a closed bell design and allows no water from the boiler above the piston. If water does get past the seals into the upper space, it's pushed out through a small breather hole on the upper backside of the cylinder (just above the bridge).

The La Pavoni levers with the 1974-2000 group have a STEAM passage to the space above the piston. This results in the space above the piston always being at the boiler temperature once air is eliminated from the system. The overheating that can occur with these machines occurs because it works too well!

HB wrote:The extra port allows you to draw water into the space above the piston from the boiler, thereby warming the brewhead very quickly. Steve Robinson (leader of the LMWDP) showed me this lever-up/down trick for tweaking the resultant brew temperature.

rpavlis wrote:The La Pavoni levers with the 1974-2000 group have a STEAM passage to the space above the piston. This results in the space above the piston always being at the boiler temperature once air is eliminated from the system. The overheating that can occur with these machines occurs because it works too well!

If you learn to control the temperature variation, you can tune shots to any coffee and enjoy different coffees at different roast levels in the same session.

Reaching the Zen Zone with a Two Switch La Pavoni

looking at that Diagram of the Cremina
i get a urge to drill a hole from below on the grouphead of my pre M model Pavoni , then plug that hole + the steam hole going to the boiler

then i would have a grouphead like the Cremina , no steam on top of the piston , but water , with the benefit of being able to cycle hot water from the boiler to the grouphead ,

why didnt Pavoni do it like that ? patent issues ?, the pre pre M model had the ability to cycle the water forth and back between the boiler

have anybody done this before ??

The physical location of the lower port to the piston seals is critical, measure and calculate many times, drill once or you make a nice paperweight.

Another approach to getting water above the piston rather than steam in the 1975-2000 La Pavoni systems would be to tap the steam hole and thread a piece of tubing and bend it so that it terminates at the same level as the inlet tube. This would be a safer thing to do with less risk of destroying the group! One might have to enlarge the boiler end of the steam port slightly to get to a size where a tap is available.

When you lift e lever on the 75-00 Pavoni almost to the water release point and lower it the group fills with liquid or a 2 phase flow of vapor and liquid as that initial vapor is passing through an orifice. Once the lever is lowered, waiting for the group to lose any temperature at all and the remaining vapor vapor returns to the liquid state. As vapor enters the group it will almost immediately return to liquid as a result of the group being at a lower temperature than the vapor in the boiler. Changes in system pressure as demonstrated by p-stat cycling will have an effect on the makeup of the group contents with no user input once the machine sets and all temperatures stablilize.

Thats exactly what we wont to avoid , because the steam constantly would carry new heat to the grouphead
the idea with two tubes did cross my mind , but i think it will be hard to get two tubes through the hole into the boiler , and it will need more parts

its only one hole that needs to be drilled , then maybe thread the drilleed hole plus the existing steam hole for some plugs , that would make cleaning easy , especially if some bigger thing would end up in the channels

OldNuc wrote:The physical location of the lower port to the piston seals is critical, measure and calculate many times, drill once or you make a nice paperweight.

There is only need for the vertical hole to be drilled ,it can be way of , as long as it ends up connecting the already existing upper hole with the existing lower hole

and it being drilled from below, it will be out of sight