When the piston is raised up all the way water rushes into the cylinder. Where does the air that was filling the cylinder go?

I've looked at pictures of many lever machine groups but have never seen an extra valve to release the air, does that mean it is forced through the coffee puck? No . . .couldn't be . . .

A bit confused, I am.

Thanks for any thoughts,

Henry

Through the coffee. If it is porous enough to let water through, then it will let air through.

after a brief respite, I'm back to being confused.

As the water rushes in to the cylinder, it would start to pool at the bottom and air would be trapped above the water. At this point, how does the water escape through the coffee? Could it be forced through the water?

I suppose if it was rushing all about in the cylinder (while it was filling) some air could escape, but once it settled the air would just get compressed above the water.

(I recognize that knowing what the water does probably won't help me or anyone else make better espresso . . . just find it interesting!)

Henry

I think in most cases, the cylinder is always filled with water.

When the lever goes up, it travels through the water of the filled cylinder, as it goes down, expelling water through the coffee, the cylinder refills over the piston, with steam pressure forcing the water in. This causes the boiler pressure to drop; so the water boils a little, the new steam takes up the extra space at the top of the boiler, and the pressure returns to normal.

another_jim wrote:I think in most cases, the cylinder is always filled with water.

When the lever goes up, it travels through the water of the filled cylinder, as it goes down, expelling water through the coffee, the cylinder refills over the piston, with steam pressure forcing the water in. This causes the boiler pressure to drop; so the water boils a little, the new steam takes up the extra space at the top of the boiler, and the pressure returns to normal.

Ok, I'm with you now. I was thinking that the piston was long enough to block the water inlet tube until the piston was all the way up. Nope!

So Lever Machines have saturated group heads!

The Olympia Cremina diagrams are awesome: this one in particular shows the internals of the group- Hydraulics

There appears to be a passage to release the water above the piston which I've never seen in a Pavoni group diagram. But la Pavoni must have something like this, otherwise it would be impossible to raise the lever.

It is still not clear to me how the air under the piston is displaced. I know from using the Presso (no laughing please) that air trapped above water will simply be compressed rather then forced out.

The only thing I can think of is that once the piston is in 'pre-infuse' position the water comes in at a terrific speed and there is enough agitation to allow most of the air to escape through the bed of coffee.

If there was a small layer of air still trapped above the water it would presumedly be forced back into the water inlet tube when bringing the piston down (before the 'valve' was closed off).

Where oh where does the air go? There must be something obvious . . .

Henry

some spring/lever groups are saturated, and some are not i think.

What about- Where does all the air come from?
You raise the piston- pulling air into the chamber

and then on my machine the cam pushes the water valve open.


so if youre pulling air into the chamber what happens to our grounds that we worked so
hard to pack nicely..

-joel

naznar wrote:so if youre pulling air into the chamber what happens to our grounds that we worked so
hard to pack nicely..

Yea, that seems strange, doesn't it? But it doesn't seem to cause much trouble. Air moves through the puck very easily, I think you'd have to really jerk the lever up to disturb the grounds.

naznar wrote:some spring/lever groups are saturated, and some are not i think.

Which ones are you thinking of? From the pictures on srobinson's Elektra/Pavoni comparison it looks like the Elektra piston might be long enough to block the water even when down all the way.

Being able to fill the cylinder with water could be useful for warming up before the first shot I guess.

Henry

The saturation thing im trying to figure out

All i know is that I was told some spring/lever san marcos had saturated groups, where hot water would be circulated around the head. Now Ive never quite understood this. Below I quote off Kees site ( check out his gorgeous spring lever hex ). The quoted I found as an option on the mirage, but i wonder if it applies to the idrocompresso?????? I mean restrictors on groups might be an entirely different thing, but if it could be applied to a spring lever group id like to know.

Secondly the coffeewater temperature reaching the ground coffee can be manipulated by altering the basic working temperature of the group. This basic group temperature can be adjusted by installing restrictors with different orifices at the rear of the group.
With different restrictors installed it is quite possible to operate one machine with temperatures adjusted differently from group to group to accommodate for the use of lighter and darker roasted coffees.

http://www.keesvanderwesten.com/index2.html


-joel

naznar wrote:( . . . ) i wonder if it applies to the idrocompresso? ( . . . )
http://www.keesvanderwesten.com/index2.html


-joel

Wow . . . I didn't realize he made a lever machine . . . beautiful!


I think that spring lever machines would be 'unsaturated' to keep the spring dry. But I have very little evidence for that (just the Elektra piston picture).

Henry

no I agree. My san marco has exposed springs, unlike Kees design.
The springs might rust if they are in water. What are springs high in again?
carbon?