Removing Bosco group sleeve - Page 2

#11: Post by **OldNuc** » September 16th, 2018, 11:47 am

EPDM and NBR are not really rated for the temperatures that are experienced in any of these groups and the failure mechanism is a rapid loss of elasticity at elevated temperatures.

September 16th, 2018, 3:25 pm

bgn wrote:Interesting. I wonder if it's as effective at heatsinking as the solid brass group. I bought a 30 year old Cimbali lever years ago and went through piston seals twice a year. The brass in the group was pitted. The Cimbali dealer found a never used group for it and I replaced the entire group. Cost me $1000. Now my piston seals are good for a couple of years. But when they leak it rusts the spring and I have to replace the seals and the spring which is also expensive. Would love a machine with a stainless steel spring.

why don't you send the spring out to have it coated? there are all sorts of newfangled coatings developed for handguns and rifles that hold up really, really well, look up the Robar company. Pick one that uses low temp curing so you don't anneal the spring.

#13: Post by **bgn** » September 16th, 2018, 4:44 pm

OldNuc wrote:EPDM and NBR are not really rated for the temperatures that are experienced in any of these groups

I have no idea what this means.

I assume it's the material that is commonly used to make piston seals (?). Is silicone better?

September 16th, 2018, 5:12 pm

Yes, that is the black material that almost all of the "U" cup or "V" cup seals are manufactured from. Silicone is a natural high elasticity material with temperature ratings of 400F+. The downside is it can be a bit fragile and damaged by rough handling and use in rough or pitted bores. In any decent condition espresso machine it will last years with no periodic slathering with DC-111(silicone based grease). They are a bit more per seal cost wise but the markedly increased service life more than makes up for that.

#15: Post by **bgn** » September 16th, 2018, 11:59 pm

Thank you for the info given here regarding seals. Very helpful. Apologies to the OP for jumping in.

#16: Post by **Bluecold** » September 17th, 2018, 1:58 am

Viton (brand name) is also a rubber type that holds up to high temperatures.

#17: Post by **OldNuc** » September 17th, 2018, 8:22 am

Viton has most of the same issues as the EPDM and NBR other than temperature, not the best choice for these types of seals in this application.

#18: Post by **Bluecold** » September 17th, 2018, 4:49 pm

I'm not a rubber expert, but the only mentioned downsides of EPDM and NBR are their temperature tolerance right? Viton is rated up to 200c, or much higher than it will ever see in an espresso machine (2.0 bar steam is 130c).

Also, to at least keep this thread slightly on course, I'd cobble together a puller with a threaded rod and some pieces of metal, wood, or plastic that fit.

#19: Post by **OldNuc** » September 17th, 2018, 5:34 pm

Resiliency, resistance to abrasion wear, durometer. The main reason for periodic removal these group sleeves is to replace the o-rings. They harden and shrink which can result in a leak.

September 17th, 2018, 9:39 pm

It's normal for seals to wear out. I have no issue with that. It is realistic that a user can replace them. But on my Cimbali the top seal leaks and rusts out the bottom 3" of the spring, which requires a tool, and a trip to a service bench. But it appears that with sleeves a tool is also needed to get it out. At least there is not the extra danger of tension like on a spring.