I am struggling with a persistent leak issue with my Caravel. After a few uses, and forcing shot that I should not have, my group head was leaking - so I ordered a replacement set of piston seals from OE, and replaced the small o-ring at the bottom of the piston. This solved the leak.

So, since then, I have found the acceptable range for my KyM and have not pulled any shots that needed a real heavy hand. So far, so good... But a few shots later, there was still some drips coming from the group head. If I filled the boiler up, I would get a steady drip, but raising and lowering the lever would either stop the leak or slow it to a minor slow drip.

A few day later, I have another gushing leak, so I remove the o-ring from the bottom of the piston, and it is ripped up, literally - as if the ring were simply two rings glued together and the inside ring came undone (I dont think this is actually what happened, as the inside of the o-ring is quite jagged).

I did not use any DOW-111 when I installed the new o-ring because I am not exactly sure what it does, nor how to use it - but now I am without my machine again. Should I bother ordering another o-ring from Orphan with some Dow-111, or is there something further I need to consider? It seems a bit strange that such an essential seal would be so prone to breaking.

Any advice?

I'm sure you've thought of this already, but just in case you haven't, I'd suggest taking out the piston, removing the circlip inside and then carefully inspecting the back the "connecting rod" where it presses into the o-ring to make sure it is perfectly smooth. Any machining defect there could be chewing up the back of your o-ring and causing the problem. I have 2 Caravels with original seals and despite buying replacements from OE on a "just in case" paranoia impulse, have never needed to change any of them.

If it is rough, a polish with automative valve grinding paste - first coarse then fine - should sort things out.

Cheers

Mike

Without lubricant you have rubber rubbing against metal. It will wear out really fast. DOW 111 is food safe lubricant. You need it.
Just coat the ring in a thin film of Dow and you're good to go.

I posted a longer reply, but somehow it got lost. Anyway, I recommend leaving an inch or two of water in the kettle, and a container under the group to catch drips. After doing this for a while my o-ring started acting better, and no more drips. Maybe it keeps them from drying out.

Also, its possible that more pressure, not less, during the pull, will keep the o-ring seated better. This might make it less likey to tear? Anyway, as I've gone more towards fuller doses and greater pull pressure, I have have not had to replace the o-ring in a long time

PC

FWIW, my o-ring (bought at OE) was leaking after about a month of intermittent use. For the last several months (also intermittent use) I've been using a ring I cut out of the rubber insert from a pressurized basket. It seems to be made of tougher material, or maybe it is seated better and the pressure is distributed better, as it has shown no signs of leaking.

This is on a mid-generation yellow Caravel.

Regards, Henry

Well, quite a situation. We feel confident that the little ring is a good fit and a good part......I recollect it being Viton which should definitely stand the temp from a Carvel. We as well have had no issues with our little ring. so there is something else in play here shredding your gasket. We'll take a look at our materials on that seal, but I am pretty sure it is temp rated far higher than the operating range of the Caravel. Even if there was a rough burr on the little nipple that fits into the ring it seems that it would not shred and disintigrate in the fashion you describe. We'll check our sourcing for this part and see if it is our end that is causing the problem.

I followed Roeland's advice and ordered a new set of rings, only this time with some Dow 111, we'll see if that does the trick.

The Caravel design where the slender o-ring sits in a groove cut into the wall of the piston cylinder, rather than onto the piston itself, is not optimized for heavy-handed pulls. The o-ring can become distended if too much force is used. Gentler pulls will reduce the distension and Dow 111 will reduce but not eliminate abrasion of the o-ring between the piston and chamber wall. If you tend to pull with a heavy hand, an elastomer with a stiffer duro might be the ticket.

As far as I understand this, the Dow certainly isn't going to do any harm, but there's little in the way of sliding on the o-ring, it's nearly all pressure, which is why the nib needs to be smooth - unless there is a temp problem.

Cheers

Mike

timo888 wrote:If you tend to pull with a heavy hand, an elastomer with a stiffer duro might be the ticket.

huh?