<15A thermostat for 1980s/1990s Conti Prestina

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jedovaty

#1: Post by jedovaty »

Several years ago I restored a conti prestina single lever, I think it's early 1990s but could be earlier, and used a pressure stat in conjunction with a solid state relay and arduino to maintain a more stable temp. This worked very well, but then I had to stop drinking coffee.

The setup is very.. unprofessional..** and I'd like to revert back to the old t-stat. Unfortunately, the tstat and its connected copper tubing were lost in a move. See attached photo - sorry it is blury, it's the only one I have.

Cafeparts has a contact thermostat, but I don't think the right part, this looks like it would need to be drilled into the boiler which I don't want to do, and it also appears to be too cold at 85C?
https://www.cafeparts.com/Contact-Therm ... duct/15984

What are current, reliable, smallish t-stats in the 15A and less range? Do I want adjustable or fixed? I'll probably have to add the plumbing of course. I don't even remember what a good temp is for these machines. hah.

Thanks for your help!

** wires all over, breadboard, etc


User avatar
civ

#2: Post by civ »

Hello:
jedovaty wrote: ... restored a conti prestina single lever ...
... pressure stat in conjunction with a solid state relay ...
That's what is usually done to keep the pressurestat contacts from damage.
jedovaty wrote: ... had to stop drinking coffee.
Sorry to hear that. =-/
jedovaty wrote: ... revert back to the old t-stat.
... tstat and its connected copper tubing were lost ...
None of those should be a problem to find.
You may have to adapt a tube from another machine.

Similar to this one: https://cdn11.bigcommerce.com/s-e8fsp2o ... 94.png?c=2

One end is for the pressurestat (1/8" or 1/4") and the other for the fitting on the boiler port.

This is how it is set up: http://www.espresso-restorations.com/im ... CN3191.JPG
jedovaty wrote: Cafeparts has a contact thermostat ...
That's a safety klixon for the heating element.
Not what you are needing.

The pressurestat in your photo looks like or is similar to a Mater pressurestat.
See http://www.espresso-restorations.com/im ... CN3194.JPG

These are highly regarded by Paul Pratt of www.espresso-restorations.com:
Paul Pratt wrote: MATER switches
These switches have been used for many years in Isomac machines and a few other professional domestic machines.
They are very similar to the CEME in size and rating. The difference is that the micro-switch looks like it can be
replaced and is easily removed from the unit by undoing the 2 screws.
See his very informative page on that: http://www.espresso-restorations.com/p-stats.html

You could use the XP110 model and reuse the solid state relay.
I understand that there are fixed models and adjustable models, you want the adjustable model which I think has a 0.5/1.2 bar range.
But no deadband adjustment like the CEME.

That's about it.
If you managed the first mod, you'll get this one done in no time.

Do let us know how you fared with this.

Best,

CIV

jedovaty (original poster)

#3: Post by jedovaty (original poster) »

Thank you!

It's been so many years, I messed up the terminology and made an error, I installed a pressure transducer, not a pressure-stat. All of it ended up working like a p-stat, except, with a tighter "dead" zone. Originally was supposed to be a tiny circuit but that wasn't working, then tried to PID but the code was complex, so we just made a very basic while loop and tightened the dead zone.

With the links you have provided, and a smaller p-stat, this will be pretty easy. In fact, I probably won't have to plumb it in, since we added a "t" fitting into the existing plumbing order to put in a vac relief valve.


User avatar
civ

#4: Post by civ »

Hello:
jedovaty wrote: Thank you!
You're welcome.
jedovaty wrote: ... installed a pressure transducer, not a pressure-stat.
Hmm ...
Neat. 8^D
jedovaty wrote: ... will be pretty easy.
To be sure ...

Just take out the transducer and using the proper elbow fitting put either the new pressurestat or the vacuum valve in its place.
But remember that it is good practise for the pipe to the pressurestat to be coiled, like the one in the link I posted.
Do show us photos when you're done.

Best,

CIV

jedovaty (original poster)

#5: Post by jedovaty (original poster) »

civ wrote:But remember that it is good practise for the pipe to the pressurestat to be coiled, like the one in the link I posted.
I saw that, and wondered what's the purpose? I searched web and only found information for HX machines, but the coil there is inside the boiler of course. It seems this would lead to cooling the water that is built up near the p-stat, but I don't see the point of this? Perhaps the slightly cooler temps gives a longer life to the p-stat? The original machine had no coils.

User avatar
civ

#6: Post by civ »

Hello:
jedovaty wrote: ... what's the purpose?
The coils keep steam from reaching the pressurestat membrane and condensing there.
jedovaty wrote: ... cooling the water ...
Cooling the steam before it reaches the pressurestat.
It is also used in manometers for that same reason and to dampen vibration when an Ulka pump is present.
jedovaty wrote: ... original machine had no coils.
May have had when new (?).
No coils = less labour = cost cut

In any case, you can get one ready made and carefully adapt it.
While you are shopping, you may want to consider using a Sirai pressurestat which may have been original OEM equipment, depending on the year of manufacture.

Check out this very interesting and informative thread by drgary: Conti Prestina Espresso Machine Restoration 101 (Completed and Indexed)

See his choice of a Jaeger pressurestat (last two or three pages) and how he mounted it.
See also this unit on sale here at HB and how the Sirai pressurestat is mounted (no coil).




Best,

CIV