Three years ago, I purchased a new PV Lusso. For about a year, the shots pulled straight and evenly. After a year, the espresso extraction consistently, started from one side of the dispersion screen, before coming out from the other side. I've noticed this side pulling in some of the older spring lever machines and suspect it has to do with spring fatigue or a bent spring. Has anyone else noticed side pulling on a spring lever machine?

Fullsack wrote: I've noticed this side pulling in some of the older spring lever machines and suspect it has to do with spring fatigue or a bent spring.

Interesting phenomenon. But I sure can't see how it could be spring related because the spring pushes on the piston, and that piston's seal is producing pressure in a hydraulic cylinder - between the seal and the coffee bed the water will assure that the pressure is the same everywhere.

P.S.
FWIW, people frequently use the term 'fatigue' to describe a weakened/deformed metal spring, whereas when engineers use the term on a spring it has to do with a condition that after many thousands of compression cycles makes it prone to sudden breakage. When springs get significantly weaker (exert less force) it's because they have deformed (shortened or buckled) by being compressed or bent beyond their elastic limit. Spring steel does not get weaker (in the sense of elastic stiffness, or Young's modulus) as a result of normal use.

Does this channeling follow the spring if you rotate the spring... say 180°?

Or, try rotating the dispersion screen 180 (without cleaning it.) One thing I can imagine would cause this is a partially clogged screen that allows the initial blast of water to disturb one side of the puck. Another farther fetched possibility - on a cylinder with multiple inlet holes you could have a seal that has worn so as to favor one inlet hole, which also might allow a lopsided initial rush of water.

Weekly, I do a Cafiza flush. When I've disassembled my machines, the dispersion screens have been clean, so it's not a clogging issue. Turning the seals and piston are interesting ideas; I'll give them a try.

The dispersion screen is clean and the piston looks level, in relation to the end of the cylinder.
Unlike a Pavoni, there is very little space between the piston and the cylinder wall on the Lusso, so yes, a bent spring wouldn't change the path of the piston. If I'd of thought it though, or pulled the dispersion screen, I would have realized, it's not a spring issue.
I will assume, the piston rod doesn't have any play in it, as it travels down the shaft. So, the water should hit the entire dispersion screen with equal force. Ruling that out, there aren't many other possibilities.
Turning the piston 180° or changing the piston seals might reveal something, but that would mean dealing with a high tension spring, something I'm not of a mind to deal with right now.

I replaced the spring on my Sama Export when I rebuilt it last year. The new spring was OEM from Ponte Vecchio, purchased from 1st Line. After about six months, the new spring definitely deformed in some fashion and I started noticing these one-sided pours. I happened to have a group seal fail earlier this year, allowing the opportunity / obligation to inspect the spring while I was in there replacing the seal. The new spring is definitely distorted to one side.

That being said, I don't notice a difference in brew pressure (I've never attached a manometer to the steam wand to confirm this, however) and the shots don't taste any different. If anything, I feel like I get more crema now...but that could just be due to improved basket prep due to 12 months more experience.

It's difficult to see how compressing the spring with the lever would apply uneven pressure - the rod, as it is lifted, applies pressure more or less in the center. But warped springs appear to be a fact. Maybe this is due to the inherent shape of the spring? Some spring mechanics out there would know more.

The same should go for downward pressure, i.e., it should be evenly distributed on the piston because there is little space for it to move from level. But perhaps a little, and that is enough?

I'll be interested to hear more about this.

PC