It is also a good idea to examine the threads in the brass casting. On one of mine one can see that the bore in the brass is slightly tapered, that reduces the thread engagement for the first one or two threads too. As pointed out in the previous post, there is about a 15 fold amplification of force because the system is really a lever, and half the force is applied to each bolt. I had come to essentially the same conclusion.

A while back I took a fish scale to determine just how much force I was using when using my machines. I found that at the recommended force the bolts were "giving" enough so that steam was beginning to come out the top of the flange when under that force. This was with the fish scale reading 15 kilos (about 150 newtons). Now with longer bolts it does not do this at all. (This is what led to my concern in the first place, along with the threads beginning to strip during a seal replacement procedure.) I was especially concerned when I remembered the flood caused by the failure of the bolts on flange on the safety shower reservior that I described earlier! It was the identical mechanical situation.

I agree that Allen head bolts also are a dramatic cosmetic improvement.

I measured the depth of threads on three different types of 6mm acorn (dome) nuts, one was ordinary steel, one stainless, one brass. Oddly, even though they were all shaped differently on the outside, they all were long enough internally so that between 8 and 9 threads were engaged, and none had a taper so they were engaged the full length. That is dramatically better than 5 or 6 threads, because the first threads maybe tapered and thus not engage fully. Hence threaded rods and acorn nuts should not present any problem at all, even with brass ones.

I think if one find steam beginning to issue from the top of the flange during the pull, one should begin to have serious concern! Longer stainless replacement bolts are inexpensive and remove the potential for failure.

rpavlis wrote: I think if one find steam beginning to issue from the top of the flange during the pull, one should begin to have serious concern! Longer stainless replacement bolts are inexpensive and remove the potential for failure.

Amen.

It is really quite easy to remove a bolt and check to see how long the threaded portion is. If it is 14mm or more (12.7mm is a half inch) it meets or exceeds the info shown on the lapavoni.it website (their parts lists show "Vite TE M6x14" for these bolts, available either chrome plated or brass plated) you are at least in accord with their design.

I found that my bolts measured about 11.5mm, so no wonder I was getting occasional steaming from the top of the flange! Since they are brass plated stainless, I can only assume Pavoni put them in when building the machine, not even conforming to their current specs! They are in my miscellaneous screw drawer now....

There are currently on eBay quite a few options for M6x16 socket head bolts, including one "button" socket headed bolt with a rounded head http://www.ebay.com/itm/171140368961?ss ... 1423.l2649. Also of interest could be the listings of this vendor http://www.ebay.com/itm/400518648476?ss ... 1423.l2649 which has hex head bolts in 14mm, 16mm, and 18mm lengths. On my machine, 18mm bolts could have been used; 16mm is probably a universal choice.

I would recommend that any Pavoni user at least check this.

If steam is leaking out at the top of the flange ,,something is not right

one thing it could be is something is un even on the back of the flange ,or front of boiler

sins if the top moves outward , the bottom must move inwards
the bolts are not moving at a pressure of 15 kilo on the lever , sins that would only give a pulling force of ca 500 pounds , and the clamp force is over 3000 pounds

if there ist a too soft gasket put in between the flange and boiler ,THAT will change the things going on
because at a normal pull we now are pressing in the bottom of the flange with about 500pounds of pressure
If it only gives away the slightest , then over time this will grow

I once worked on some steel constructions
they where bolted together with 16 M40mm bolts each at ca 1000 nm
but sins the steel was painted , the clampforce went down for the next 14 days , then they had to be re torqued
then again after a month,,simply because the paint did flow

The area was about 40cm x 30cm and 16 bolts used


if i was adding a gasket between the boiler and group , i would look up the max torque using the longest possible threads in the boiler

here preload really matters ,and the choice of gasket material

M6 x 16mm socket head bolts ordered! I have been a little squeamish about the torque that is out on these bolts since I added a 1/16" PTFE gasket.

Plus they will look better. Thanks for this and all the other Pavoni threads, Robert.

Pete

I just pulled my MY2000, pressurestat/pre-M Europiccola apart for a six-month clean and inspection AND to replace the Ryton piston that came with it, with the shiny new brass one that Santa picked up from Stefano for me... and I remembered this post. So I went and picked up a couple of stainless M6 Allen screws with a bit longer threaded area. Inspection of my group indicated (thanks to Robert for tipping us off), that there was a lot of threaded depth in the boiler side that was going unused by the short stock bolts.

I hope the stainless alloy is not _more_ reactive with the brass of the female boiler threads than ordinary high strength steel. It is my understanding that stainless steel is more reactive with aluminum than high-strength steel. But I don't know if that holds for brass or the plating on our machines.

As for all the mail ordering, you shouldn't have to for this. A good old fashioned little hardware store _ought_ to have what you need. The little True Value store in Boulder City, NV (our lake house, where my Pavoni lives), has a HUGE selection of loose bolts, properly organized. Big Orange and the Big-L are nearly worthless in comparison, (ask me how I know). Might be worth striking up a relationship with the small local business for things like bolts. BTW, nothing against the big guys, just play to their strengths and buy what they are good at selling. For small purchases of small bolts, the little guy rules that roost.

-Peter

Stainless in contact with aluminium can produce problems for the aluminium, not the stainless. Stainless in contact with ordinary steel often presents a problem, because the stainless can then develop rust. Ordinary steel can have serious problems in brass. (It is a good idea to replace ordinary steel threaded rods on many brass portafilters with brass or stainless ones.) The original bolts in my La Pavoni boilers were stainless.