Here's an odd question.
let's say you have an HX machine which uses a pressure stat and you want to upgrade it, but a larger P-stat like a Sirai won't fit the machine.
Is there a way that the pressure stat function can be performed external to the machine? Is this a place where a PID would work?
I PID HX machines all the time. The pstat is almost as accurate as the PID, and since exact control of the boiler temp in the HX isn't as critical as a SBDU or DB, if it ain't broke don't fix it.
But I have other reasons for replacing the pstat with a PID.
NOISE! The Sirai has 3 mechanical relays that open and close often enough, and loudly enough, that they had to go. It doesn't
COMPLETELY silence the HX, there's still the auto-fill solenoid & pump noises, but it does make the HX much more welcome in my kitchen!
here's a simple wiring diagram for PIDing the HX.
edited: Want another reason to replace a defunct pstat with a PID? The pstats rubber diaphragm is the part that fails most in consumer/commercial espresso machines. The diaphragm kit is fairly inexpensive to replace in Sirai pstats, but there are no kits for most other brands, so it's necessary to replace the whole thing. A PID will last indefinitely in my experience, in fact I have one that's been in use 24/7 for three years without a hiccup.