I've posted some stuff about my Z11 LE project in the Z9 thread but I thought I would start a new thread as this may be of interest to others using commercial levers at home.

I had made great strides recently, to the point where I was producing coffee with the machine but tonight I ran in to electrical problems, burning out 2 pressurestats and making the garage go dark. I am taking the machine to a guy who actually knows what he's doing to get this sorted, but it happens that this guy knows his onions when it comes to installing PIDs. He's not trying to sell me this idea, I'm just weighing up my options.

So given that a traditional pressurised lever machine controls its brew temperature by dissipating heat through the group and therefore brew temp depends not only on boiler temp but also workload and, to some extent, ambient temperature, would there be any advantage in fitting a PID to control the boiler temperature?

As my machine will be used at home in my garage, largely for my own entertainment until such a time that my ambitions bear fruit and it gets pressed into commercial service, I hope that it may allow me to adjust the temperature to warm the groups more quickly and fine tune according to ambient temperature. As an example, last night I was making coffee like a kid in a sweetshop as I'd just got it going but the air temp was hovering just above freezing and I could not get enough heat into the group to get anything but sour shots and a water temp boost for flushing could have been just the ticket.

Is there any validity to my pontificating or would this be a largely pointless exercise?

Others have PID'd lever espresso machines, so why not? Digital temperature controller on a lever machine and Has anyone ever PID'd a lever machine? discuss the whys and hows. On the other hand, a pressurestat reacts more quickly to temperature (pressure) changes and placement is irrelevant versus a thermocouple that can measure only one point.

Cheers for the links Dan, really should remember to UTFS. Hadn't considered the advantage of pressurestat vs thermocouple, but then a pressurestat is not really practical to adjust on the fly. I shall give this much thought I'm sure.

PID hasn't got diaphragms and contacts to wear out. And it is silent.

frustrated_uk wrote:Hadn't considered the advantage of pressurestat vs thermocouple, but then a pressurestat is not really practical to adjust on the fly.

You could use a pressure transducer and have the best of both worlds, though it could be cost prohibitive. See PID with pressure sensor instead of thermocouple and Controlling steam boiler with PID and pressure transducer? for previous discussions.

orphanespresso wrote:it nearly drove me crazy with the continual on and off of the element as it worked to maintain that exact temperature setting. Every 5 seconds or so the element would turn on and then turn off right away .....it was a pretty high wattage for our kitchen circuit and with each turn on the lights would dim and then brighten up when the element turned off. It eventually maintained a very even temperature of the boiler but it does seem that it would take a lot of experimentation with a pid on the boiler to get the group temp right.

Why did this drive you crazy? Just because your lights dimmed? Seems like they must have dimmed with a pressurestat as well, albeit less frequently. I believe that is a sign of insufficient wire gauge in your circuitry. Shouldn't be a problem in Europe where the voltage is 240VAC rather than 120VAC.

Also, why should it take extra experimentation? You have a pressure gauge on the machine whether you use a pressurestat, thermostat, or thermocouple-driven PID. The temperature setting on the PID will correspond directly to a steady-state boiler pressure, and the group will idle at a very consistent temperature--in fact, exactly the same temperature as a pressure-stat controlled boiler, if it could hold such a narrow temperature band. If your shots are too cold, up your set point by a degree or so till you see an 0.1 bar rise on the gauge. This is a lot less trouble than re-setting a pressurestat (as you said), and I'm confused why there ought to be any extra experimentation anyway.

With a PID, if the thing isn't responsive enough for you, you can always just tweak the PID parameters. You trade responsiveness for accuracy, so back that off and you'll have a more responsive setup with some overshoot on temperature.

You can also use a PID as, or install, an electronic thermostat. Set a narrow band and it mimics a pstat.

Sensor placement is important. It's not a bad idea to sketch out the boiler and heating element location with the expected thermal eddy pattern.

orphanespresso wrote:I agree also, the element does not care what is telling it to turn on and off.

Not to be too nitpicky, but as a matter of interest—in some sense it does, and using a PID with electronic switching apparently extends the life of the heater due to the reduced thermal shock and the efficiency of the switching, which as I understand it is timed to coincide with the 0V point on the AC cycle.

The machine I was experimenting with has no pressure gauge so I had overlooked the idea that you would be setting temp and monitoring both the pressure and the temperature. Does seem like a nice advantage. With no pstat a lot of the dialing in of the temp behavior when pulling a shot has been worked out with group flush times etc, so I have gotten more or less used to the idea of working these things out without a lot of sensors on the machine in question.

What kind of sensors? FWIW, if you have a PID you can pretty accurately use this Saturated Steam Temperature <-> Pressure calculator (found via Dan as usual ) to extrapolate your boiler pressure from your PID setpoint (or more to the point, the actual probe temperature reading displayed on the PID). I believe this may not be 100% accurate, depending on where you stick the probe, i.e. at steady-state I think there is a temperature gradient top to bottom in the boiler such that the saturated steam in the top is hotter than the pressurized liquid in the bottom. I have no idea what that differential is or how big of a deal it is, but I bet it's within the margin of error on your average cheap espresso machine pressure gauge, so I doubt it matters.

I still don't see the reason for burying the settable pstat so deeply in a machine that it is inconvenient to change the setting.

I imagine the reason is that for the Italians it's a set-it-forget-till-the-maintenance-guy-comes thing, and that's why they don't bother making it more accessible. Still, I agree it's unfortunate that they do it that way.