Well, while I was working on the La Pavoni tonight (to clean up the piston stem seal and remove a stuck lever pin), the circlip snapped in half. This prompted me to start fiddling around and I have decided to make a few mods:

First, I'm going to install some bronze bushings in the holes for the lever. I actually found what appear to be the perfect size on Amazon.com. I'll post the exact part numbers later. I was originally going to buy them from mcmaster.com (along with the replacement circlip, etc.), but Amazon had the exact size I needed, while the mcmaster ones would have needed milling. Since the holes in the steel of the handle are a bit elongated, I think the bronze bushings will be a nice upgrade. I'm just going to drill out the existing holes (in order to enlarge them slightly) and then press the bronze bushings into place. I also found a near perfect replacement for the roller bushing that moves back and forth in the group head lever slot (photos coming soon).

As mentioned, the cross pin on the back of the lever was stuck in the larger round bushing that rides in the group head. Luckily, I was able to press it out using the chain breaker/riveter for my motorcycle (see pictures below). Specifically, it's the Motion Pro Jump chain breaker. Anyway, it did a great job pressing the pin out.

Second, in addition to installing the bronze bushings (which I will have photos of next week, once I'm all done), I decided I would see about making an adjustable pressure regulator. What I decided to do was install an adjustment screw that allows you to vary the pressure on the OEM La Pavoni pressure relief valve. As you can see from the photos below, the relief valve is just a spring that presses against a 9/32" steel ball bearing. The ball seals the steam relief hole in the boiler.

In order to install an adjustment, I drilled out the hex cap for the pressure relief valve and tapped it to M10 x 1.50mm. I have also ordered a 10mm long M10 x 1.50mm allen screw, which I will use as the adjuster. I will have to shorten the length of the spring a bit, but if all goes well, it should allow me to vary the pressure at which the relief valve kicks open.

I'm not 100% sure of the exact effect changing the pressure relief setting will have (because there are many variables), but in the most simplistic terms (and after looking over this link that outlines Gay-Lussac's law), the basic concept is that lower pressure equals lower temperature. There's a formula which states:



So just off the top of my head - using the ratio in the formula above - if T1 (temp 1) is 180 degrees when P1 is 1 bar, then if you adjust the new pressure (P2) down to something more like .95 bar, then it follows that you should end up with a temp of around 171 degrees.

That's my story and I'm sticking to it...

Either way, it will be fun to have an adjustment on the La Pavoni and see if it makes any difference in the shots and/or if it allows me to leave the machine on the "I" setting for multiple shots, without having to turn the power on/off in order to keep the temperature down a bit when pulling 5 or 10 shots.

I've also ordered a Reg Barber C-flat 49.6mm tamper (Rosewood & stainless). Hopefully this will help a bit with the very mild channeling I have been experiencing near the very outer rim of the portafilter basket.

So that's what's on the agenda as far as mods go As some of you might recall, I recently made my own bottomless portafilter for the La Pavoni, which has been working great. I think between the naked portafilter, the new tamper and being able to dial down the temp a bit, the shots will be even better soon; we shall see.

Here are some pictures from tonight's work. As soon as the rest of the parts start showing up, I'll post some updates and of course more photos.

Ray

Here's the chain breaker, setup on the La Pavoni so I can press out the stuck lever pin


Finally! The pin is free (you can see it poking out of the right side of the press)


Here's a shot of the pressure release cap after drilling and tapping a M10x1.50mm hole in it


Here are the guts of the pressure relief mechanism. A M10 allen screw will allow for adjustment soon.

Nice post, and the mods described are very interesting, as is your use of motorcycle tools . I can't wait for you to turn up with a modified Ohlins or WP rear shock to control a spring operated group head .

Your formula from Gay-Lussac is correct, however do not forget to work in Kelvin, or your calculations will be off (different 0-point).

Nice post Ray! Look forward to seeing results the adjustable pressure regulator/relief valve mod.

Just wondering if you checked out this thread on nutation? It may help with the channeling. In that thread, I brought up:

KnowGood wrote:The only way I would believe any and/or all of this is if your sidewall of your tamper was angled and not straight. Hell, you almost have to have no sidewall for this to work properly! When you "nutate" the top edge is connecting with the filter basket leaving a gap between your effective edge, the bottom, which is the one that counts - just look at the diagrams posted and you can see this.

Dan replied with a pic of a tamper that I think actually helps:

HB wrote: Seriously though, the only tamper I have with a clearly angled side is the TORR:

cagiva905 wrote:Nice post, and the mods described are very interesting, as is your use of motorcycle tools . I can't wait for you to turn up with a modified Ohlins or WP rear shock to control a spring operated group head .

Your formula from Gay-Lussac is correct, however do not forget to work in Kelvin, or your calculations will be off (different 0-point).

Thanks! And thanks for the tip about Kelvin. I was just going based on a ratio in the formula and not trying to get the exact temp using an ideal assumption based on condition, etc. With the heating element constantly pumping energy into the water, I'm sure it's pretty difficult to pin down an exact temp. However, the basic idea is less pressure = lower heat. That (and the new tamper) I think will help improve the shots a bit more

Ray

KnowGood wrote:Nice post Ray! Look forward to seeing results the adjustable pressure regulator/relief valve mod.

Just wondering if you checked out this thread on nutation? It may help with the channeling. In that thread, I brought up:

I'm giving the Reg Barber C-Flat tamper a try and see how it works. I ordered 49.6 mm for use on the basket I have. I have some very slight channeling on the outside edge from time to time, so I'm hoping the larger diameter and the curve might help a bit. We'll see

Ray

The parts I was waiting for arrived today. Here's a quick snap shot of the "finished" adjustable pressure regulator on the La Pavoni. I currently have a different spring on order though, so there is still some fine tuning left to be done. For now, I just clipped off some of the factory spring in order to compensate for the extra 10mm length of the allen head adjustment screw.

Video coming shortly!

Ray

And here is the video I shot tonight...

I still have some tweaking to do, but so far so good!

Hello:

A really great job there ... =-)
Very neat.
At some time I thought about something similar for my Shirley but got stuck when trying to decide just how fine the thread had to be, ie: turns/mm advance, as the spring is rather shortish.

Please do post your adjustment results.

Cheers,

CIV

Hi Carlos,

Thanks a lot!

Yeah, I originally wanted to use M10x1.25 for this (or even x 1.00mm), but the stainless steel allen head set screw, which I wanted to use, was only readily available in 1.25mm pitch (at least from the place I tend to order parts from - http://www.mcmaster.com ).

As a result, I just went with 1.50 pitch (not my first choice, but also not the end of the world either - at least as far as this project is concerned). Using a pitch of 1.50 mm, as you may know, just means that for each 360 degree revolution of the nut/bolt, it will advance (or recede) 1.5 mm. A pitch of 1.25 mm would result in a movement of 1.25 mm per revolution. So if you look at it from that standpoint, the different in travel between a 1.5 mm pitch vs. a 1.25mm pitch is only .25 mm per each revolution (that's roughly .010"). Perhaps more importantly, each 1/4 turn of the adjuster (in this case, my little allen set screw) - even when using a coarse pitch of 1.5 mm - still works out to a distance of only .375 mm (or about .015"). I'm sure, given the Nm of the spring, we could work out the exact change in tension, but at some point it becomes academic right?

The bottom line is that any adjustment is better than no adjustment and the different between using one pitch verses the other really just boils down to how fine grain the control is (i.e. will you have to tweak the adjustment by 1/4 turn or only an 1/8th of a turn, etc.)?

In my case, I just wanted to have some fun and see if I could lower the temperature a bit. It doesn't need to be super exact. Just ball park sort of stuff it plenty fine with me. I'm sure the heat in the boiler swings around quite a bit on its own anyway (since there is really no other form of monitoring or adjusting it).

I may attempt to take some temperature measurements. The other thing I was going to do was install a pressure gauge (in order to adjust the boiler based on pressure), but I may have to find a better source for the M12x1.00 gauge adapter first.

Ray

Seems like an interesting idea....however remember this is also the safety valve for the boiler. I got a lot of grief here for adjusting the opening pressure on my safety valve. Didn't stop me, but your system if it jams for any reason could lead to a boiler explosion. I would probably "T" off boiler port and add a back up pressure relief valve set slightly higher than the max you will want for coffee.