There has been a little confusion in discussions as to whether or not the boiler cap on the Pavoni Romantica and the Gaggia factory have an anti-vacuum function.

Turns out that some do and some don't. HB member hankbates clearly showed that his 1999 Romantica has no anti-vacuum in the cap (see: La Pavoni lever history--age of used machines)

However, my cap (which may be a non-stock replacement) and other caps pictured in posts (see Any help diagnosing my faulty La Pavoni?) look the same, but have an anti-vacuum function built into the sealing part. Here's a picture of mine taken apart -


Note the bottom right piece is not a simple rubber seal. To tell which kind you have you don't need to take it apart. Just look at it from the inside, and if you see plain red rubber, you have no anti-vacuum, but if you see a brass button then you do. The replacement caps (appx $45 US) that I've seen online all look like they have anti-vacuum.

A cautionary note - these things are adjustable with a 4mm hex key. If you want to take it out be sure to carefully caliper its depth before you unscrew it so you can get it back to the same over-pressure setting where it was originally.

If you have a standard Europiccola or Pro, you most likely do not have an ant-vacuum valve. But there is one available and which I believe comes stock on the Stradivari. It is Valv. di sicurezza con antivuoto - part #396754 in the Pavoni parts list, is item 19 in the pic below.

It would also be possible, I think, to make a tiny version of the combination vacuum relief and air bleeding system as used in pressure cookers to put in the steam release valve like this. It would probably also require making a different nut that holds the original spring and ball or spring and teflon mushroom in place because this would be thicker than the ball or teflon mushroom. (While one was doing that, one would probably also put a stainless steel set screw in the new nut to permit adjusting the release pressure!)

The things in pressure cookers are closed by the high volume of steam that begins to be released when the water beneath truly begins to boil. They typically use only gravity to open and close.

Another thought is to put such a thing into a lathe made brass cap, or to put one of the valves from a single pipe steam radiator on a such a brass cap. One could also put such a thing onto the top of the sight glass.

Now I guess the question is whether you really need anti-vacuum on these things. I suppose that if you turn the machine off and walk away enjoying your coffee without emptying and cleaning the PF it could be an issue. Your boiler vacuum would raise the lever and pull gunk up from the spent puck into your brew chamber. I always always clean my PF and screen after a shot. But sometimes I forget.

Yes, one should always immediately remove and wash the portafilter whilst it is still hot anyway!

Another thing one can do is put a really heavy brass handle on the machine. I did this for a while, but after I had ebony portafilter handle, ebony steam knob, and ebony boiler cap I put an ebony one on the group handle too. One problem with auto bleed would be that it would not bleed the upper part of the group, and this is very important too.

rpavlis wrote:One problem with auto bleed would be that it would not bleed the upper part of the group, and this is very important too.

Good point, hadn't thought of that. On a pre-M it would, because the top of the group cylinder is vented back to the top of the boiler. But on Millennium groups you have that siphon tube insert

in the group neck and there is no channel between the group and the boiler other than the siphon tube. But I guess even there it would not be under much vacuum, maybe just enough to support the column of water pulled up the tube. Not enough to raise the lever.

homeburrero wrote:There has been a little confusion in discussions as to whether or not the boiler cap on the Pavoni Romantica and the Gaggia factory have an anti-vacuum function.

Turns out that some do and some don't. HB member hankbates clearly showed that his 1999 Romantica has no anti-vacuum in the cap (see: La Pavoni lever history--age of used machines)

However, my cap (which may be a non-stock replacement) and other caps pictured in posts (see Any help diagnosing my faulty La Pavoni?) look the same, but have an anti-vacuum function built into the sealing part. Here's a picture of mine taken apart -
<image>

Note the bottom right piece is not a simple rubber seal. To tell which kind you have you don't need to take it apart. Just look at it from the inside, and if you see plain red rubber, you have no anti-vacuum, but if you see a brass button then you do. The replacement caps (appx $45 US) that I've seen online all look like they have anti-vacuum.

A cautionary note - these things are adjustable with a 4mm hex key. If you want to take it out be sure to carefully caliper its depth before you unscrew it so you can get it back to the same over-pressure setting where it was originally.

If you have a standard Europiccola or Pro, you most likely do not have an ant-vacuum valve. But there is one available and which I believe comes stock on the Stradivari. It is Valv. di sicurezza con antivuoto - part #396754 in the Pavoni parts list, is item 19 in the pic below.
<image>

From many different posts I have learned that there were significant problems (many were replaced under warranty) with the boiler caps on the LP Romanticas and Gaggia Factorys, and this was even mentioned as one of the reasons why the LP importer has discontinued selling this design. Until I saw this post (I also hadn't seen the earlier post) I wasn't aware that the design had changed.

Both of my 1999 vintage Romanticas have the earlier design, and neither has given any problem. When I bought a spare cap (off eBay, the plastic cover had broken) I took it apart and concluded that the problems were primarily related to cover failure. Now I am wondering if the problems really started with the redesign.

And also, if the above is correct, why the redesign? It wasn't until much later that LP started incorporating vacuum breaks in other models, and it appears that it has only occurred on the Stradivaris? Why fix something which wasn't broken (many on these posts question the need), and substitute a more complex design? I think that the letters "CE" on the caps shown in the earlier post is a possible answer. Around this time the European electrical equipment safety approvals authority "Cenelec" started exerting its influence on all sorts of devices, and the vacuum breaker requirement may have become a required part of the design of electrically fired boilers. The company I worked for at the time had a lot of problems adapting their viscometers to Cenelec standards; merely meeting Underwriters Laboratories standards did not suffice.

I'd be interested if you could post a sketch of how the rubber piece (it replaced the red rubber soft seat in the older models) is constructed; could the small (floating? not spring loaded?) VB flap or plunger be prone to sticking in the open position?
If it does stick open, you have a cap which no longer seals, and also one which the manufacturer doesn't want (for safety and liability reasons) the user to tamper with. It was provided from the factory glued together....

I wonder how the vb function works in the stradivari design? Could it be retrofit into an earlier machine? Would it even work in a 2 element 2 switch machine, with its constant steam flow to control pressure?

I love these machines, so simple, but also so complex.

Are we making progress? Yes, but it seems like we are just as confused as ever, but on a higher level, about more important things....

hankbates wrote:I'd be interested if you could post a sketch of how the rubber piece (it replaced the red rubber soft seat in the older models) is constructed; could the small (floating? not spring loaded?) VB flap or plunger be prone to sticking in the open position?

I'm not good at drawings, but it can be easily described. It isn't spring loaded, just picture a tiny brass disk earring with the post going through the center of the rubber membrane and a button on the back. Gravity opens it, and when you shake the cap you can hear it rattle back and forth. I know from experience (and from reports on this forum) that it can stick open. In my case I just gave the cap a rap and it came unstuck.

My only knowledge of the Stradivari design is from parts pictures, including this one from 2005 for the Europiccola, Pro, and Mignon: http://www.espressoservices.co.uk/RIC_E ... sional.pdf, so I think it will easily retofit into earlier models, and may be a stock part on later models, especially if as you suggest it's needed to meet a European safety approval.

hankbates wrote:Would it even work in a 2 element 2 switch machine, with its constant steam flow to control pressure?

I don't see why it would not work on one of these, unless it has a problem with prolonged exposure to a steam blast*.

On another HB thread there is discussion by Cremina owners that if you have an anti-vacuum cap you don't need to bleed off initial air pressure. I guess the argument is that the water is boiling for a good while before the AV closes and the air is displaced by vapor. Not sure if that's true for this cap, I always let off a few seconds of steam anyway as part of my cup warming process.

*edit addition - looking at the parts list, it appears that it might only pair with a spring that is intended for a higher pressure than you have in the older dual element, no-pStat, hissing models.

homeburrero wrote:I'm not good at drawings, but it can be easily described. It isn't spring loaded, just picture a tiny brass disk earring with the post going through the center of the rubber membrane and a button on the back. Gravity opens it, and when you shake the cap you can hear it rattle back and forth. I know from experience (and from reports on this forum) that it can stick open. In my case I just gave the cap a rap and it came unstuck.

My only knowledge of the Stradivari design is from parts pictures, including this one from 2005 for the Europiccola, Pro, and Mignon: http://www.espressoservices.co.uk/RIC_E ... sional.pdf, so I think it will easily retofit into earlier models, and may be a stock part on later models, especially if as you suggest it's needed to meet a European safety approval.

It looks to me when you look at the parts lists currently on the lapavoni.it website, the whole relief/vb assembly carries all of the same part numbers (body, spring cover, element) whether EP, Pro or stradivari. However, a completely different assembly (body, spring cover and element part numbers are all different from above) is shown for the Mignon, and this element appears to be the same mushroom as in earlier LP's. Looks like you have to replace the whole assembly, means going inside the boiler. It doesn't seem like a good idea for the double switch machines to go thru all that for something which may not take the continuous steaming anyway....

It now looks to me that when they made the change to vacuum breakers, they did it on all models, not just the Strad. They don't appear to be offering the Mignon any more, so they still offer the old valve as a spare part.