I decided to give the CMA lever another go this morning.
I cranked the portafilter in a little tighter and had no leaking past the group gasket.

Brazil Organic Fazenda Colina on 2 days rest.

First shot was...a little slow. Okay, a lot slow. Almost choked it, but it eventually relented.
Shot volume was low. Weird. Where did it go? I think I may try loading a blank portafilter into the group and see how long it holds pressure.....if the lever goes up, the water must be migrating somewhere (past the piston seals? back into the boiler?)

The shot was slow, but the taste? it wasn't overextracted...but it wasn't wow.
Next shot, loosened the grind a little bit.

Still took a long time, but not quite as long, shot volume about 1oz...
but WOW! Thick syrup. And sweet like syrup. An incredibly rich and flavorful shot.

I loosened the grind a bit, then as I was dosing, I realized I'd been dosing kinda heavily, used to my C85...so I knocked it back to 3T (from 4T). Still filled the double PF nicely.

Now I see what you guys have been talking about when it comes to lever machines.
Why can't they all be like this? Wow wow wow, just wow.

(Note: I'd never really had a lever espresso before)

Technique - any CMA spring lever techniques? Tricks?
What pressure do you operate your CMA lever at? I'm at 1.0-1.2

Punch list:
I still have a small steam leak at the pressurestat...
Need to test the overpressure valve (dial the adjustment back until it blows, then dial forward a bit).
Need to test the overtemp cutoff; I figure some gentle heat with the heat gun will help, with a thermocouple on the device to make sure I don't bake it too much, and see what temp it really trips at
Need to get the seals for the steam/water wands and install them.
Then button up with the metal skins (now cleaned)
Need to run a drain tube into a bucket (no real drain near where I'm running it, but I do have water)
Maybe repaint the original skins.

I love this machine

I don't blame you. Great espresso from CMA.

I had mine at 1.2 but now run it at .9. I had dialed it down to .7 but recently I was finding the lever was migrating up to a higher position before resistance when released from preinfusion. I figured the preinfusion was less at .7 bar so maybe the volume of water rapidly entered the puck thereby allowing the lever to rise higher? (Does that make sense.) I change the seals and relubed but there was no evidence of leaking. I even check the ball antireflux valve but there was no hint of cofee there so I figure no leak across it.

If you updose, then the volume of each lever pull will be less, no? There is a nice diagram that an HBer posted on that thread about temperature profiles of the lever group that I had started which is nice to use to conceptualize where the water goes during a pull.

Congrats on getting to experience CMA espresso.

I'm glad to see you are enjoying your CMA. I've really loved the performance of my Astoria.

In terms of shot volume, the higher the dose, the lower the volume. The water volume is determined by the space between the top of the puck and the bottom of the piston. Geometry tells me that a one millimeter increase in the height of the puck is about a two and a half milliliter decrease in the water volume. Unfortunately geometry doesn't tell me how much that millimeter weighs, so I can't tell you how much to change your dose. I'm usually somewhere in the neighborhood of 16 to 16.5 grams, but it does vary by more depending on the coffee.

If you decide to do your experiment with the blind portafilter basket, make sure you hold the portafilter handle the whole time, because it will probably start to unscrew. I have caught mine attempting to release on choked shots and don't really want to know what it looks like if it sneezes under full pressure.

I keep the boiler pressure around .8 to .9 bar as well, it seems to be a good compromise for the brew temperature. Just keep in mind that you will need to adjust based on ambient room temperature, a cold room will cool off the group faster. I don't have any secrets to share, you just have to dial in until you've got the best shot you can. Just remember that increasing the dose raises the brew ratio more than you would expect because you are also decreasing the volume. Smaller changes work better than big ones.

Jim

Not sure I follow the updose/shot volume connection. Does that hold true irrespective of basket size? For example using a triple basket instead of a double basket?

It holds true for the same basket but a change in basket sizes follows similar principles.

The total volume of water available for the shot is the quantity between the shower screen and the bottom of the piston, a constant, plus the quantity between the shower screen and the top of the puck (headspace), a variable. If the dose is held constant, then you will have more headspace in an 18 gram basket then you would in a 14 gram basket, and therefore have more water volume. If you were to keep the headspace constant between two different sized baskets by changing the dose, then the water volume would be the same (assuming both baskets have the same diameter and wall shape.)

It isn't a perfectly linear relationship because of water retention in the puck and puck expansion when wet, but it's close enough for government work.

Jim

Thanks Jim. Makes sense. Considering the above, then why all the fascination with double pulls and Fellini moves if the shot volume is fixed. Wouldn't seem to change anything.

I wonder if the Fellini moves are some way to attempt to get more water and less air into the cylinder, though I'm not sure how that would work.

No matter how you slice it, air is lighter than water, so you have a buffer of air above the column of water in the cylinder. That takes up room too, but less if compressed...

I wish we had a transparent piston machine to see the insides at work...

Jack, I agree with you that the piston stroke should be the volume of the shot, but in my experience that isn't the case... I increase the shot volume more by decreasing the dose than can be explained by the difference in absorption. Also, I still have significant flow after the point where the spring has fully expanded. If I were to guess, I would say that is caused by steam pressure rather than gravity. It would also explain why I have a dry puck all the way down to about 12 grams in a 14 gram basket, even though there is enough room for a swimming pool on top. As for double pulls, I agree that the purpose is to force more water into the puck and create more space. I tried it for a while on my Astoria, but always seemed to get side channeling, the puck would literally lift from the sides from the negative pressure. It wasn't every time, but it was enough to give up on it. Also, I have no trouble getting a true double without it now so I gave up trying, I might have mastered it with more work.

Allon, I didn't mention the air above the water column because in theory, the volume of air will be constant as long as the boiler pressure is constant. It shouldn't have an effect on total water volume.

Jim

This is an interesting discussion. Perhaps a diagram previously posted by Emil in the thread mentioned above can shed some light on the system, quite nicely put into words by you, Jim. (thanks for that)



Where does air enter? I pull the lever with the portafilter loose, then lock it in before it reaches the valve open down position. I think I am limiting the air passage through the puck, during the upward movement of the piston. There is water in the group between shots. For example, if you loosen the screw at the ball bearing valve, water passes out of the group as air enters the ball bearing valve.