In the lengthy & recurring thread, "La Pavoni Pro in the hands of pros", Doug Garrott ("orphanespresso") recently wrote, "Though they [La Pavoni] have tried to address the temp issues, and most people don't appreciate the plastic piston and liner, so that's the thanks they get for trying!"

I had thought the move from brass to plastic was not a design improvement intended to rectify any problem, but rather simply a cost-saving move with no upside user benefit. And so, like a number of other folks around here with the plastic piston, I looked forward to swapping out mine and coverting "back" to brass... In fact, I recently had my plastic pistons replaced with brass in both of my Gaggia Factory machines when I had the machines in for other service issues...

Well, so far I've been pleased with the change, though I really can't say I notice all that much of a difference either way.

But Doug's comment got me thinking that there might actually be trade-offs, making the brass vs plastic piston issue not quite so one-sided or so clear cut.

And so, I thought it might be interesting to start a separate thread, listing/discussing the pros & cons (preceived and/or real) of the two different types of La Pavoni pistons.

Here's my crack at a preliminary list...

Brass Pro / Plastic Con: With a brass piston, there's more metal in the group than with a plastic piston & plastic sleeve, thereby decreasing the tendency to overheat

Brass Con / Plastic Pro: With a brass piston, as heat is transferred to it, there's more hot metal in contact with the water in the group than would be the case with a plastic piston & plastic sleeve, thereby increasing the tendency to overheat

Brass Pro / Plastic Con: The brass pistion avoids the problems reported with the plastic piston unscrewing

Brass Pro / Plastic Con: The brass piston seems to have more "heft" in the pull (though does it really, or is it just imagined?)

Brass Con / Plastic Pro: The plastic piston is inside a plastic sleeve which might result in a smoother pull than with the bass piston which has no plastic sleeve

Brass Pro / Plastic Con: In general, brass seems to be a more durable, stable and long-lasting material than plastic

Brass ? / Plastic ?: Clearly the expansion/contraction characteristics of the two materials when exposed to heat are quite different - would these different expansion/contraction characteristics differently impact the pressure on the o-ring and/or either the quality of the resulting "seal" or the feel of the pull as the group's heat builds?

So...
- Comments on any of these items in the list?
- Suggested additions to the list?
- Suggested deletions from the list?
- Discussion of how many angels can dance on the head of a piston?

r-gordon-7 wrote:Brass Con : With a brass piston, as heat is transferred to it... ...thereby increasing the tendency to overheat
Brass Pro / Plastic Con: The brass pistion avoids the problems reported with the plastic piston unscrewing
Brass Pro / Plastic Con: In general, brass seems to be a more durable, stable and long-lasting material than plastic

The two latter pros far outweigh the former con, for me. Durability and dependability are far more important than not having to learn how to manage heat accumulation.

For me, quite a bit of thermal management comes from knowing when to turn off the button, and *timing between shots.


*Since I'm the only one that drinks (almost always) espresso drinks at my GF's house, it's usually just the right temp by the time I turn it back on and make all the rest of the preparations for my second capp of the morning. And yeah, I know that that may just be me...

I cannot say why- but I have found the older the pavoni- the better the shot. The oldest Pavoni I have goes right back to the early 60's and it performs better than any other I have used.

I definitely would prefer a brass piston. To my mind what heat reducing capability plastic may have would be outweighed by all the cons. I also think it would be a negligible reduction in temp...

Indeed I generally found a Pavoni works best if you are only making one or two shots- and for this I imagine having a brass piston actually helps- as it absorbs excess boiler heat at the critical point before the water hits the coffee bed. After a few shots it may have the reverse affect- holding excess heat in...

Richard,

Excellent post. I just bought a second Factory 16, this one with both pistons (brass installed), so I'm anxious to see the difference once I get back home (in Iraq for a few more months). I'm of the opinion that I'd prefer the brass piston for longevity purposes, and if that means tweaking my routine a little to deal with heat issues (aside from the current ones), so be it. If it doesn't work out, I'll swap it out to the original plastic. Highly doubt that will be the case though...

Psyd wrote:*Since I'm the only one that drinks (almost always) espresso drinks at my GF's house, it's usually just the right temp by the time I turn it back on and make all the rest of the preparations for my second capp of the morning. And yeah, I know that that may just be me...

Agree, and it's not just you. I usually turn the machine off while frothing and leave it off until I'm ready to pull another shot. When I'm ready for another cappuccino, I flip it on to warm back up, and by the time I'm done preparing everything for a shot, it's ready to go. No overheating issues with the way I use it; however, it would not be my machine of choice while entertaining, but then again, that's not what it was designed for.

Bang for the buck, it's hard to beat...and a looker too!

Pretty comprehensive list Gordon, and am in agreement with all here. I owned both the pre millenium and Millenium machines, and have since sold off the Millenium one.

I much prefer the brass machine, with the frequent unscrewing of the ryton plastic piston driving me ever more to the point of dispair. I certainly noticed little difference in temperature management between the two machines, and even less difference in "pull smoothness" as you had suggested as a possible pro point for the plastic.

Perhaps the final thing to say is the fact that Pavoni have now gone back to a brass piston across all models (including the Stradiveri model) I think nails it once and for all for team brass!

Having said all this of course, plastic Pavoni's are certainly not bad machines, but if there is a choice, brass would be the sensible option

Great help guys. I have a plastic piston pre millennium Pavoni, and have been wondering for some time now whether I have been missing out with the not having the millenium model. Having read this post I am going to keep my pre millenium model, and replace the plastic piston with a brass one. Great work.

I have the Pavoni Pro with plastic insert. Not having had a brass piston it is hard to make comment on the pros and cons of each.
I suspect that the plastic liner and piston are an attempt to produce an insulated water chamber within the group. i.e. the water inside the plastic sleeve will not be the less than the temp of the body of the group. This is borne out by the fact that I can leave my unit on for 45min and still pull a couple of good shots. Sure subsequent shots will deteriorate as the water pulled into the sleeve is pulled from the boiler and eventually heats up the insulated chamber, but I can turn on the unit before breakfast and have a great cup when I'm ready.
The other pro of the plastic liner maybe to do with the disturbance of the puck when water flows into the chamber. The plastic liner forces the water to flow around the sides of the liner to prevent digging wholes in the puck.
I have spent quite a bit of time disassembling the group and playing round with the position of the sleeve within the group, ( have some pics if anyones interested). The position of the sleeve certainly plays a large part in the size and pressure of the shot I guess because it is effectively altering the length of stroke.
Never had a problem with the unscrewing thing but have learnt it's a big mistake to put any MolyKote 111 lubricant on the screen gasket, you definitely don't want that screen pushed out and it is a bloody fiddly gasket to put in albiet the PF -basket can be used.
Look forward to those that are upgrading ? to the brass setup to see how they find it.
Cheers Andrew

180degrees wrote: I have the Pavoni Pro with plastic insert. I can leave my unit on for 45min and still pull a couple of good shots. Sure subsequent shots will deteriorate as the water pulled into the sleeve is pulled from the boiler and eventually heats up the insulated chamber, but I can turn on the unit before breakfast and have a great cup when I'm ready.

Same here. I have a Gaggia Factory with the plastic insert and plastic piston, and sometimes leave the machine on for an extended period of time with no significant overheating issues. Eventually I will "upgrade" to the brass piston, but for now it is working perfectly well.

I have spent quite a bit of time disassembling the group and playing round with the position of the sleeve within the group, ( have some pics if anyone interested). The position of the sleeve certainly plays a large part in the size and pressure of the shot I guess because it is effectively altering the length of stroke.

Any chance you can provide said pictures?

180degrees wrote:This is borne out by the fact that I can leave my unit on for 45min and still pull a couple of good shots.

That is certainly interesting Andrew. I could not achieve that with my former Pav EP Millenium edition - it would just overheat. Can I ask is this from the time you first turn on the machine in the morning? Or if you pull one shot, leave it on for a further 45mins and then pull another shot, would the 2nd shot be fine temp wise?

I am just wondering whether it really is the plastic sleeve that does this, or the fact that trapped air/false pressure has not been cleared from your first shot, therefore keeping a lid on pressure and therefore temperature.

From my understanding of the millenium group, assuming that any false pressure has been cleared, that the water inside the sleeve comes from boiler water and water from outside the sleeve (as there is that hole half way down the ryton sleeve, as well as holes at the top of the sleeve). When the piston is cocked, the water above the piston head gets pushed out back into the boiler and outside of the sleeve, allowing for 'new' water to enter under the cocked piston head via that same hole half way down the sleeve, which has come from water 'sitting' outside of the sleeve. If the machine has been idling for 45 minutes at superheated temperatures (which is the boiler water temperature used for steaming), the whole group will simply overheat due to its direct connection with the boiler, and with no thermosyphon loop to regulate the group temperature, the water will be too hot.

But that could be just my machine, and possibly not all plastic/mliienium Pavoni's are alike! Glad you are enjoying your Pav. They are great machines and if you can master these things, you can take on just about anything

Some interesting points

ziobeege_72 wrote: Can I ask is this from the time you first turn on the machine in the morning?

Yes just from the first turn on, subsequent shots are being filled from the boiler and will like the brass thermally coupled piston be too hot after 45min.

ziobeege_72 wrote:45 minutes at superheated temperatures (which is the boiler water temperature used for steaming)

I believe the temperature target, depending on the variable beans,temp,humidty etc, is in the 195-200F range. Now if water boils at 212F under no pressure, then under pressure of 1 Bar, does it boil i.e. change to steam, at a lower temperature of 190-200F ? I should look it up but the relationships of temp V's pressure is just physics. But I think thats right, I'm sure there are many who could correct me if I'm wrong

ziobeege_72 wrote:the water above the piston head gets pushed out back into the boiler and outside of the sleeve, allowing for 'new' water to enter

That's true. I need to get my photo's organised (may take a couple of days) to help with this.
But the top of the sleeve sits pretty much at the top of the group body i.e. well past the top of the water inlet from the boiler. The stepped top of the sleeve ,when cocking the piston, is the channel by which the water is ejected and it is at this point that the water enters below the piston. The ejected water I think is cooler than and displaces the water outside the sleeve. Though the group may now warm this water it will start from a lower temp, hence a cooler water applied to the puck.
Maybe the way to prove/disprove this is to try 2 different draws.
1. Lock in PF, Slowly cock piston, express.
2. Raise piston to just before water enters, Lock in pF, finish cocking, express.
The longer exposure of the ejected water to the heat of the group and groupwater will mean a higher temp for the 2nd method of expressing.

I'm not too sure that the plastic sleeve will do much in the long run for keeping the unit cool, but does give a little more latitude at startup. Whether the extra fiddlyness in maintaining and cleaning the group with insert is worth it is anyones guess.
Cheers Andrew