Cafelat Robot Piston Seal Life - Page 5

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Nate42

#41: Post by Nate42 »

Sorry about the crappy cell phone photo. And the dirty Robot. Hey it gets lots of use. :) Anyway you can see the whitish band in the seal which I assume is a stretch mark. It doesn't quite extend all the way around it the photo is of the most noticeable spot.


Jonk

#42: Post by Jonk »

If you want to clean the tube you can unscrew the fitting and flush some water through it. That's the way I do it because I don't have any spare tubing and the supposed damage you can cause if you remove it from the fitting. The slimy old fines that came out was not very appetizing so now I use a paper filter on top of the puck in order to avoid buildup in the first place.

jpender

#43: Post by jpender »

Nate42 wrote:...you can see the whitish band in the seal which I assume is a stretch mark. It doesn't quite extend all the way around it the photo is of the most noticeable spot.
Oh, okay, I've seen similar whitish areas on a couple of my seals. I never thought of them as stretch marks, just some sort of deterioration. Maybe it's due to friction?




And I had no idea coffee could get that far up the pressure tube. How does it travel that far? Could it be evidence of a leak?



When I removed the tube from my Robot the dirt only extended about 1cm. I wonder if there is something different about your routine vs mine? I can't imagine what it would be though.

Nate42

#44: Post by Nate42 »

I've always had water most of the way up the tube. Never saw it as a problem. I do make it a point to fill as full as I can manage without overfilling, so not much air in the system. Also not too much of a stretch to imagine an old seal (I used my first one for over a year) being watertight but not airtight, so most of the air gets purged out. Which again I don't see as a problem in terms of overall performance of the system.

The tube doesn't look as bad in "real life" it's more discolored than it is "full of crap". I probably should try to clean it sometime I guess. Always intended to eventually replace it with the kit for the armored version. I'm sure the insides of the pressure tube in my HX machine are just as bad, you just can't see it. Maybe I'm gross but it doesn't really bother me. :D

Jonk

#45: Post by Jonk »

I guess it's caused by air from the tube leaking out somewhere. Took a few months at least before I saw water that far up the tube. I was a bit concerned it might damage the gauge, but it's been years without any further issue.

jpender

#46: Post by jpender »

A high fill shouldn't matter. I have almost always filled to within 0.5cm of the rim. At that level, assuming half of the gas is water vapor, you still have effectively ~6cm3 of air. The tube has an internal volume of around 0.6cm3. The fittings and gauge add a little to that. So at 8bar you would expect little to no travel up the tube. In theory.

Unless there is a leak. If your piston seal allowed all the air to escape -- which you would probably hear -- then water might travel 7/8 the way up the tube. But if air is leaking out up by the gauge then maybe it would be quiet enough that you wouldn't notice.

If you put in a new seal does the water still go up the tube?

Jonk

#47: Post by Jonk »

jpender wrote:If you put in a new seal does the water still go up the tube?
In my case, yes. No audible clue. I think the way push in fittings work is that they seal under pressure, maybe that tiny amount of air can escape before there's a proper seal? Especially if the tube is a bit worn. If the gauge eventually breaks I'll use it as an excuse to buy a better one: https://www.naked-portafilter.com/produ ... gauge-kit/

jpender

#48: Post by jpender »

Jonk wrote:I think the way push in fittings work is that they seal under pressure, maybe that tiny amount of air can escape before there's a proper seal?/
I'd be surprised if that were true. It would be crummy product if the seal relaxed every time the pressure dropped below some threshold.

I have a few of these fittings in a bag. I just tried pushing a tube into one and seeing if it leaked when submerged while I blew into the end of the tube. At best I can generate about 2psi by blowing into a tube as hard as I can. So blowing gently is going to be well below 1psi. No bubbles escaping. I disconnected it, reconnected it. Still no bubbles.

So if it leaks I think it's not normal. It's a failure of some sort. If it were mine I'd try to fix it.

Jonk

#49: Post by Jonk »

That may be. Just read this on https://www.cafelat.co.uk/blogs/cafelat ... vs-regular:
It is also perfectly normal to see water inside the flexible tube.
Not sure if it's Pauls writing or not..

jpender

#50: Post by jpender »

Maybe my theory about the amount of air above the piston after you lock-in is wrong.