Piston and valve sealing problems with many lever machines

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rpavlis
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#1: Post by rpavlis »

It has been 5 years since I purchased an used 1999 "real" brass La Pavoni Europiccola. Since then I have added to the lever collection by getting two older La Pavoni machines and a new Micro Casa a Leva.

When I first got the 1999 machine it was an example of the horrors of using ultra hard water without descaling. Not only was the boiler full of scale, the walls of the group and even the piston seals were covered with the stuff! There was some corrosion on the group walls. The seals on the piston were actually torn from rubbing against the scale on the group wall. I managed to get rid of all the scale, but the wall of the piston cylinder remained rough. This was hard on piston seals! One day I took sandpaper and sanded off the wall so it was not rough, and then went to finer sand sand paper, then steel wool, and then "Bar Keeper's friend". Then for a final touch I used Simichrome polish! I was concerned that all of this would result in an out of round and irregular diameter group wall, but the inside micrometer showed that things were not as bad as I had thought they would be, the bore was still very close to round and constant diameter along its length. When I reassembled the machine after that there was practically no resistance to moving the group handle when the machine was not under pressure. I always polish the walls of the group with "Brasso" at each servicing now.

I had abnormally many seal failures before polishing up the walls. I learned to recognise instantly when this would occur--the lever would push easily at first, very "spongy", and then suddenly lose all traces of sponginess. At a very specific instant the handle would just "sink" two or three centimetres. If I would look into the boiler after this the boiler water was murky. I did not realise what was going on when I first got the machine, and did not realise one should look into the boiler often. A lot of "coffee gunk" soon was all over the inside of the boiler. I finally drained the boiler completely and added about 50 mL of 190 proof grain alcohol. I shook it around for a while, and then drained it. I added about 25 mL more alcohol, shook it somemore, and again drained it. I rinsed it out with tap water until everything was clear. Then I drained it and put in my usual 1 mM potassium bicarbonate water. I now look into the boiler at least once a week, though I have come to recognise seal failure generally before the boiler is contaminated so badly that it needs an alcohol wash!

I recently had another weird sealing problem--the steam valve on the 1999 La Pavoni. I noticed I had to tighten the seal nut more and more to prevent leakage. There was a bit of steam leakage from the steam wand too, though not much. I disassembled it and discovered that there was a lot of tar and hard deposit both on the valve sealing surface and on the shaft going through the seal. I do not know where the deposit came from. I put some alcohol on a "Q tip" and tried to clean out the bore as best I could. The deposit on the valve sealing surface, and expecially on the shaft was amazingly hard and resistant. The problem was that it was irregular, hence there were leaks. I had to use fine sand paper on both the sealing surface and shaft surface, and even then it took a lot of turning against the sand paper to get off the deposits. The rough deposits on the shaft had mostly destroyed the seal. I once again used steel wool after the sand paper, and then good old "Bar Keeper's friend." When I reassembled it the valve securing nut only needed to be turned enough so that there was just detectable resistance when turning the knob. There were no leaks.

I have become convinced that keeping surfaces against seals of various seals must be kept very very clean and polished. We do not notice that we have to turn valves harder and harder to close them, because it happens slowly. We also do not notice that piston seals begin to show more and more resistance.

(I noticed hard deposits beginning to form on the MCAL cylinder wall as well. Once again it was time to polish the cylinder walls.) Problems of this sort seem essentially universal with lever machines. Because the spring provides the force it is more difficult to recognise problems. It is also difficult to look inside the MCAL boiler, I use a rifle bore illuminating light.

forbeskm
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#2: Post by forbeskm »

I have not had your experience with the group head. I have been fortunate that the machines I get are just lightly scaled in the boiler. You have some good tips. I am starting to rebuild 5 Pavon's this week, 74, 76,77, 78, Frankenstein and a LaCara and will make sure the groups are sparkling.

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hipporun
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#3: Post by hipporun »

With the most recent Pavoni I rebuilt, scale did find its way to the piston seal. Fortunately, no corrosion had taken place in the boiler or group.

Good stuff rpavlis. Thanks for posting.

jtrops
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#4: Post by jtrops »

I haven't had the scale problems in the cylinder, but I have the plastic sleeve so I guess that would be a bit of a stretch.

I have had the coffee gunk in the boiler problem, and the way you describe the lever feel when it's going bad is exactly what I experience. What I've started doing is pulling the piston rod pin and pushing the piston down until the end of the rod is level with the top of the slot. The lower gasket is exposed by doing this, and it allows me to run a q-tip with silicone grease around the seal. When I push the piston up it travels high enough to lube the upper seal as well, and then the whole thing goes back together. It takes only a few minutes to do it, but it fixes the backflush that seems to bet getting gunk in the boiler.

It's interesting that you wrote this today since I just had to do it this morning.

Jerry

Joeydiepe
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#5: Post by Joeydiepe »

how do you clean de grouphead after polishing it with brasso? Just some soapy water?
Joël

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rpavlis (original poster)
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#6: Post by rpavlis (original poster) »

I just cleaned it with soapy water and then rinsed it very well.

Joeydiepe
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#7: Post by Joeydiepe »

This is what my group head looks like. After this photo I scrubbed the scale line off with the help of some diluted vinegar.
Is it usual to get this reddish color (corrosion/copper re-deposit) in the group head? The brass on top of the piston also used to be discoloured, but it comes off pretty easy with some fine steel wool.



Joël

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rpavlis (original poster)
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#8: Post by rpavlis (original poster) »

The cylinder walls on my La Pavoni seem to stay smooth, though I always polish them on major servicings. Pits in any cylinder wall are bad because they can be the site of the so called "bronze disease" caused by the catalytic action of CuCl. Pits caused by this will grow, that is why it is called a "disease." They need to be polished out when tiny. They can generally be avoided by being careful to have chloride free water.

The last time I replaced the lower piston seal I used the top seal from an earlier complete seal change that still seemed in good condition; this was a few months ago. Today this seal failed. Those new to La Pavoni machines might not recognise the instant sympton: The lever "gives" when one starts the pull, and then suddenly the "giving" stops. After this the boiler water will quickly begin to turn brown. Again, this results in "varnish" covering the inside of the boiler, and eventually foul taste. Fortunately I had a spare seal. It is probably a good idea to keep some in stock. One can change these seals in just a few minutes.

Some lever machines have the top side of the piston exposed to boiler water and steam (like the La Pavonis of all three generations.) When seals fail on these the boiler gets contaminated. Some other lever machines (like the Micro Casa a Leva, MCAL) operate so that the top of the piston is exposed to the atmosphere. When seals fail on this latter type of machine, the water that gets by the piston will come out the vent in the side of the group. On the MCAL this vent is on the back of the group just about even with the top of the mounting flange. (Open top piston designs require more for force to move the piston because boiler pressure is added to the pressure when the top of the piston is open to the boiler.)

DanoM
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#9: Post by DanoM »

rpavlis wrote:On the MCAL this vent is on the back of the group just about even with the top of the mounting flange.
My Strega has a similar vent to outside design when the top seal fails to seal. I had that happen just yesterday, and you should have seen my wife's eyes! :shock: She thought the machine was "broken" badly.

Quick removal of the group lever, cleanup and proper lube this time around had the machine back in service quickly. Last time I was a little light on the Dow 111 for a good seal, so knew right away what the issue was. My seals are getting a little stiff too, so it's probably time to order a backup set.
LMWDP #445

OldNuc
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#10: Post by OldNuc »

Piston lip seal service life in all of these machines is ridiculously short for their cost. It is a material application issue.

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