Anybody else see this pattern of seal failure on a type 1 piston? Got ideas for solutions? That took about 6 weeks to happen.



Looks to me as if the holes between the boiler and cylinder nibbled at the seal.

Holy crap! That is weird. I have never seen anything like that. I am trying to visualize what could make those symmetrical grooves. Do you know what orientation the seal had inside the group? Is that the top or bottom seal? It is catching on something. Does the piston action reflect this? I mean, can you feel any hiccups in the piston movement? Can you feel up inside the group cylinder and feel any burrs?

I am sure you have thought about all these things, but I just can't wrap my head around how this could happen. They are like espresso crop circles to me.

Pete

Bottom seal, and though I haven't measured to any degree of precision, it looks to be about the distance between the outside holes of the water inlet. Did not feel any "hiccups" or catching in the lever movement. lAlso found what would appear to be one of the "slugs" inside the boiler. Some sort of burr on the edge of those holes? I hesitate to take an abrasive to the interior of the cylinder.

The lower seal can catch on the openings in the group where the lever attaches, but this only happens when the piston is installed. You sure this didn't happen immediately and not over time?

That would put the "bites" 180° from each other, and these match up pretty well with the two end water inlet holes. Definitely happened over time, though, not immediately, as there was a sudden loss of pressure while pulling a shot.

I need to source some seals in number so I can do some testing. Now that Doug and Barb are only selling master kits with mostly seals that I won't need, it's a little pricey to get, say, 6 or 8 of the u-cups.

The white U cup seals that Kurt August sells in the buy/sell forum are really robust and fit just right. You may want to contact him about gettin some.

Pete

So, I'm not the only one having trouble with my Caravel seals. I manage to break the tiny o-ring on the bottom of the piston every couple of months (probably from too fine a grind, I guess). But, part of the upper seal of the piston gets "shaved" by the groove on top of the sleeve when I put the piston back in place. It's as if the seal was a little too thick.

For reference, my piston is the second one from the left:


(picture from sorretinacoffee)

So if you find a cheap source for individual seals (or the tiny o-ring) let me know.

Did you find out if yours was damaged by the water inlet holes?

grainger.com sells o rings. The tiny o ring is 4 mm and they do sell them.

They seem to be safe for use with water but would they be suitable for use with boiling water?