Sorry about the pun, it's just too much caffeine in the system as usual. It has to go somewhere
Anyways: after a looong hiatus, I have finally gathered up the guts to fix the broken C-ring in the Strietman ES3 piston, using the spare parts graciously sent by Strietman himself. After removing three years (bleeerrhh) worth of oxide and salts from every copper and brass surface and changing the gaskets, the WS3 was finally put to the test again.

And I ran in to the same problem as just before the first c-ring breakdown: trapped air in the piston.

Have tried searching around for others with the same problem, but can't find any. Maybe I just used the wrong terms, or maybe I am indeed alone with this problem. I thought this would be the best place to find out.

This is what I do. Since I am used to the Caravel, and well acquainted with the feeling of doing a pull with trapped air in the piston, I started by pulling up the lever fast, expecting to hear the burbling sound of water rushing down the piston. It doesn't come, so I surmised this is the wrong way of going about it on the ES3 (as it is with the CT1, I guess), so I started pulling up slowly instead. But no matter how I do it, I keep getting air trapped. Sometimes I can get most of it out by knocking on the side of the machine or by doing small downward/wiggling movements of the lever, but almost every time as I start seeing drops forming on the bottom of the filter I also see - and hear - bubbles come out.

Is there anyone else that's had this problem? What did you do to avoid it? I thought the problem might have been build-up inside the piston, but not anymore, it's not there now after the mega cleaning session.

Edit: should add that this is ES3 #6, so it's one of the early ones. I used it for about 4 months before the C-ring broke (the early ES3 lock rings were made out of brass, the replacement is stainless steel and much more durable).

OK, it's two days and something like 15-20 shots later. I get less air trapped in the piston now, but it still comes and goes without me knowing exactly what causes it.
This is what I did so far:
Preparation
* dose: 15 grams, weighed before grinding. (I tried more and less but found 15 works better so far).
* grind in the HG1, stir/mix (currently with a Chinese chopstick), level by knocking down filter on bench, tamp with the Strietman tamper
No obvious channeling when pulling the shots or looking at the puck afterwards, so I think we're good with the prep.

* Pull: after load and lock, slightly move upwards a little bit, hold still for a few seconds, then continue slooowly upwards.
* stop when wooden lever handle is about 15 degrees up from horizontal. If bubbles start coming up from inside the piston, wiggle the lever just a little bit up/down to help release trapped air. If more bubbles come up as I wiggle, try knocking on the side and wiggle a little bit more. If not, carefully but decidedly start pullin down.
* watch as the first drops form under the filter. If I was lucky, there is no air bubble in the central drop.
* If not, I try stopping, wiggling again and knocking to let that air bubble out the top, but usually at this stage it's only one way out: down in the cup. It will spray small drops of coffee on the side of the cup, and the crema will disappear quickly.

Edit: from experience with the old Caravel, I have learnt exactly how the pull feels when there is air trapped in the piston, so there is no doubt the same thing is happening here. I suppose several other Caravel owners know what I mean, it's a spongy, springy feeling, you can't miss it. And at the end of the pull the trapped air leaks out with a "TSSsssss".

zix wrote:* Pull: after load and lock, slightly move upwards a little bit, hold still for a few seconds, then continue slooowly upwards.

Mats,

When you begin to raise the lever, do you detect the small center valve in the piston opening before the piston starts to move up? If you try it without a portafilter, you should see a small stream of water coming from the group screen. I believe that is what prevents air from getting in the group.

On my CT1, I never detected any air in the group. I used about 14 to 15 grams of coffee, depending on the brand of beans, for a 28 to 30 gram extraction. I used a very light tamp, just pressing lightly with my fingertips on top of the base of the included tamper. After inserting the portafilter with basket, I raised the lever slightly to open the small center valve in the piston, waited one to two seconds, fully raised the lever over about four seconds, waited another three to five seconds, and then I would begin the pull, easy at first, then up to full pressure, and then easing off towards the end. My total shot time from the initial lifting of the lever to the end was usually about 35 seconds, and I adjusted the grind depending on how hard it was to pull and how it tasted.

Rocky

Rocky, thanks for replying! I have tried it, but more by coincidence than really doing it a couple of times and actually noticing the results. When cleaning out the group, I've done it. Twice since Saturday.

With the valve, I guess you mean the small knob that sits inside the small center/lower gasket of the piston, and that it should move up a little bit and let the water run down and fill the lower part? Yes, in this case water should be running down, and I suspect this detail is the very thing that doesn't quite work as well as it should .
I can really only guesstimate from what I've noticed when cleaning the group, but he guesstimate is it works as expected about, say, 3 times out of 5.
I have done a thorough cleaning and then put a small amount of Molykote/Dow Corning 111 on all parts of the piston before putting it back together, and thought it looked like it moved around nicely in there, but maybe I was wrong... maybe the inner cylinder sticks to the sides of the outer cylinder and doesn't move as much as needed... I thought that part ought to be thoroughly engineered-the-heck-out-of, to misquote Matt Damon... But that is more of a question for Wouter, naturally.

zix wrote:With the valve, I guess you mean the small knob that sits inside the small center/lower gasket of the piston, and that it should move up a little bit and let the water run down and fill the lower part? Yes, in this case water should be running down, and I suspect this detail is the very thing that doesn't quite work as well as it should.

That's right. If you recently replaced that little bottom seal, it might be sticking a bit and need some cycling to loosen it up. I would try a faster movement upward initially to see if that will release the center valve without raising the piston. I'm probably not explaining it very well. You mentioned asking Wouter, and that sounds like a good idea. He has always responded to my emails quite promptly.

Rocky

Wouter already wrote me, before I even had put an email together. He's a great guy He has the same advice, a quick knock upward at first to release the valve. I'll try it and see how it works, lots of guests coming in today so I'll have many chances to raise the lever but not so much time to check how the pour goes...