La Pavoni Europiccola: Got a brass piston, do I need thread locker?
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pcrussell50
- Posts: 4035
- Joined: 15 years ago
Y2000 Europiccola, with pressurestat and single power switch, but pre-millennium group and removable steam wand.
It came with a plastic piston, which was partly unscrewed from the plunger when I got the machine off ebay back in July. During the initial teardown, inspection, and re-assembly, I screwed it back on without thread locker, and it has worked great ever since. But "Santa" read my mind and knew that one day I would need a brass piston, and so he picked one up from Stefano, and now I have one.
I have read on here that one of the tendencies of the plastic pistons is that they eventually unscrew, which was exactly how I got mine, when I got it from ebay last July '13. But now I'm getting ready to put on the brass piston.
Am I to assume that since the brass pistons are not known to unscrew, that I therefore don't need thread locker for it?
-Peter
It came with a plastic piston, which was partly unscrewed from the plunger when I got the machine off ebay back in July. During the initial teardown, inspection, and re-assembly, I screwed it back on without thread locker, and it has worked great ever since. But "Santa" read my mind and knew that one day I would need a brass piston, and so he picked one up from Stefano, and now I have one.
I have read on here that one of the tendencies of the plastic pistons is that they eventually unscrew, which was exactly how I got mine, when I got it from ebay last July '13. But now I'm getting ready to put on the brass piston.
Am I to assume that since the brass pistons are not known to unscrew, that I therefore don't need thread locker for it?
-Peter
LMWDP #553
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rpavlis
- Posts: 1799
- Joined: 12 years ago
I would not put thread locker on them because if you use the stuff it becomes difficult to take the thing apart again. The brass one is unlikely to come unscrewed. It only needs to be tightened hand tight, and not gorilla strong then. I have usually put a phillips screw driver through the hole in the rod, and turned the piston down by grasping it until it is tight.
The problem with the plastic piston seems to be often misunderstood. The polymer used has a glass temperature of about 83C. Above that temperature the material softens more rapidly with increasing temperature, and thus begins to creep. (Even though polyphenylene sulphide has an unusually high creep resistance.) This creep slowly deforms the threads in the polymer until they are loose. In reality it was a bad use of polymers. The deformation also eventually leads to failure of the part.
The problem with the polyphenylene sulphide sleeves on the 2001 unward groups is much less severe, because the deforming force is not as high and because the temperature is usually less than 100 degrees. The pistons in the 1974-2000 groups are subjected to temperatures of about 116 every time one turns on the machine, if the pressure setting be the usual 0.8 bar or so.
The problem with the plastic piston seems to be often misunderstood. The polymer used has a glass temperature of about 83C. Above that temperature the material softens more rapidly with increasing temperature, and thus begins to creep. (Even though polyphenylene sulphide has an unusually high creep resistance.) This creep slowly deforms the threads in the polymer until they are loose. In reality it was a bad use of polymers. The deformation also eventually leads to failure of the part.
The problem with the polyphenylene sulphide sleeves on the 2001 unward groups is much less severe, because the deforming force is not as high and because the temperature is usually less than 100 degrees. The pistons in the 1974-2000 groups are subjected to temperatures of about 116 every time one turns on the machine, if the pressure setting be the usual 0.8 bar or so.
