Hello dear home-baristi,

It's a fact: pressure stats have a limited lifetime due to the mechanical nature of their microswitch.

One solution is to change the whole system with a TC and a PID, but then the problem is: where do I put this TC ?

I was wondering if it would be possible to create a digital pressure stat using a boiler pressure sensor and a PID: you get the convenience and reliability of a PID/SSR combo but without the hassle of finding/installing a TC...

I don't know the price for such pressure sensors that would operate in high temperature, but I think this kind of equipment is broadly available for central heaters found in many houses.

A TC costs a few dollars, and every off the shelf PID controller connects to it. A pressure transducer cannot be connected directly to inexpensive PID controllers. Instead, you'd need to hook it up to a 4 to 20mA transmitter adding a few hundred dollars to the cost. The hardware needed to seal a TC into the pipe for the old pstat is a lot cheaper.

Pressure reacts faster than temperature to energy changes in a boiler, and is more uniform throughout; so it is the better control variable. An electronic system could be mass produced as cheaply as a temperature based system, but unfortunately, that's for espresso machine manufacturers, not hobbyists using off the shelf furnace controls.

There's also the question of need.
The e61 uses thermal inertia of the group to smooth out boiler temperature variance. When it takes about 52 minutes for the group on the Vibiemme to stabilize, boiler perturbations of ±0.5° every few seconds have minimal effect on the group brew temperature.

As Einstein said, "... as simple as possible, and no simpler."

Thank you both.

The idea was not to improve the thermal stability of the boiler, but to provide a more robust and quieter solution than the pressurestat on my Pavoni. As an added value it would have provided a pressure gauge and more flexibility in adjusting the boiler pressure.

I have seen a pressure sensor (industrial grade, totally overkill) for about $200 which would do the job, but I don't think the usual suspects (Watlow, Fuji, ...) will work since they are designed to work with thermocouples. Maybe I should look for a general purpose PID, but I don't know the prices and the sizes (I really like the smal form factor of the SD3C).

At $200, the sensor should be putting out a standard controls signal, either 4 to 20mA (1 to 5 volt) or 0 to 10 volts. If it isn't, you are getting royally ripped. These standard signals work with every PID controller, including the 1/32nd DIN Fujis.

I kept the pStat along with the PID to have walkup brew temps and easy return to full power steam.
HX Heaven or 1½ Boiler

Yes, indeed Jim. Here is the PDF: https://www.distrelec.com/distrelec/datasheets.nsf/WebAttachments/4931CF9E9162F119C12570EB00383D3C/$File/Midas_dat_e.pdf

I am sure I can find cheaper elsewhere, since the supplier is well known for its shocking prices, but it has everything in stock and can deliver the next day in Switzerland (where I work). Well the only question is: do I need this, and right after, can I afford it for fun ? (I am wondering if I should save for a conical doserless grinder, upgraditis made another victim since I saw the Nino is finally coming...)

Ian, the idea is to get rid of the pressurestat... I could use a dual set point PID if I wanted to do something similar to your great Domobar Super.

We use the AST pressure sensors, so it was something I considered to get instant response on pressure drop for steaming. One of my main criteria was the PID had to be unobtrusive.
At the time, I couldn't find a dual setpoint PID that wasn't half the size of the Vibiemme.

Thanks Ian

So you mean you are using an AST pressure sensor instead of the thermocouple in your Domobar ?

As for the PID, it seems the Watlow SD3C can do it as stated here: http://www.pidkits.com/sd3c.html