I've been meaning to do this for a while, as I thought other La Pavoni owners might find this sort of information helpful.

In my experience, maintaining the proper temperature on the La Pavoni can be pretty tricky (especially with the older I/II switch models, where you don't have the luxury of a pressure stat). In fact, as some of you may know, temperature control (or the lack thereof) drove me to install a PID controller on my machine. I found this not only to be a big improvement on the La Pavoni, but it also allowed me to clearly see that boiler temperature and boiler pressure are tied together, very closely, at all times. In fact, the correlation is so direct that, by simply using the chart provided here, you should be able to surf the temperature on your machine to within 1 degree.

Naturally, this chart doesn't speak to the temperature differential between the boiler and the group head, but it at least will help you get in the ball park as far as where the boiler water temperature is (assuming you have a pressure gauge installed, of course). In the future, I do plan to rig up a thermocouple into the portafilter basket, also. Once that is functional, I may come back and produce a chart showing the temperature drop between the boiler and the group head as well.

For now, however, I give you the following chart, which shows the water temperature inside the boiler, based on the pressure shown on the gauge. This data was taken from my La Pavoni Europiccola, which has a PID controller installed on it. Naturally, your mileage may vary, but I think it should apply pretty closely for most users.

To produce the chart, I increased the temperature on the PID controller by two degrees at a time and then allowed the machine/temperature to stabilize for a few minutes (before taking a reading and going up to the next highest temperature - 2 degrees at a time). Please note that my machine does have an adjustable pressure regulator on it (which may slightly impact the data), although I don't think it should have too much effect as compared to a "stock" La Pavoni.



The above temperature readings are from an RTD sensor, which is installed through the base of the boiler and which is in direct contact with the water inside the machine.

Anyway, if you are attempting to temperature surf (and have a pressure gauge on your machine), then the above chart may serve to be a handy reference. Usually, I run my machine at 232.0 degrees to 233.5 degrees (depending on the coffee bean being used), which seems to work pretty well for most medium roast beans. Keep in mind, also, that this chart was produced at approximately 800 feet above sea level.

Ray

Um, the relation between steam pressure and temperature is a the same whether the steam is in a La Pavoni or anywhere else. You can find the data in a steamtable or calculator; these have been around since the late 1700s, when steam engines were invented.

Great contribution, Ray.

This makes it much more inviting to temperature surf a pre-Millennium model with a dual switch!

another_jim wrote:Um, the relation between steam pressure and temperature is a the same whether the steam is in a La Pavoni or anywhere else. You can find the data in a steamtable or calculator; these have been around since the late 1700s, when steam engines were invented.

None of your charts and links match the real world results that I see every single day with my machine - not even close. Your second link there deals with saturated steam. In the La Pavoni boiler, you are dealing with a system that has water and steam and which is not a closed system (i.e. it has a pressure regulator involved, heat is being lost, etc, etc.).

For example, on your second link (the calculator), it indicates that 1 bar equals 212 degrees (i.e. water boiling). However, when the boiler on the La Pavoni is at 212, it's barely showing any pressure inside the boiler.

No disrespect intended (I respect the information you provide on this forum), but as far as temperature surfing your La Pavoni, I think the links above are pretty much worthless in the real world.

Ray

another_jim wrote:Um, the relation between steam pressure and temperature is a the same whether the steam is in a La Pavoni or anywhere else. You can find the data in a steamtable or calculator; these have been around since the late 1700s, when steam engines were invented.

Keep in mind also, Jim, that steam is not what is being driven into the group head, it's the water (under the steam) in the boiler. The readings above are the water temperature in the boiler, not the temperature of the steam.

Ray

RayJohns wrote:For example, on your second link (the calculator), it indicates that 1 bar equals 212 degrees (i.e. water boiling). However, when the boiler on the La Pavoni is at 212, it's barely showing any pressure inside the boiler.

but it is at 1 bar -- atmospheric pressure.
I think you might be confusing absolute pressure for gauge pressure. You'll want to subtract 1 bar from those tables.

allon wrote:but it is at 1 bar -- atmospheric pressure.
I think you might be confusing absolute pressure for gauge pressure. You'll want to subtract 1 bar from those tables.

I'm not really sure, but I didn't see anything in those links that looked like it equated to my chart above.

On the calculator link (for example), I just input 232.0 F for the pressure and it returned 1.4881 BAR. If you subtracted 1 BAR for atmosphere pressure, then you end up with .488 BAR. However, on the gauge (when the boiler water is at 232.0 degrees), the pressure is always .62 BAR.

On the PDF table, it shows a lot of information, but none of it seems to match what I am seeing.

Can you give me an example, using Jim's links, of how to calculate my boiler water temperature via the reading on the gauge? I mean, if it's such an easy calculation to make (as Jim suggests), then can you use the links provided above and reproduce my results? For example, produce a chart showing what the gauge should read for a specific temperature.

So far, I'm not seeing it. I'm not saying it can't be done using the links Jim provided, but I just don't see where it matches up. It seems to me if it's such a snap to calculate the boiler water temperature based off those steam charts, then people would be doing that every day (i.e. using the pressure on their gauge to mathematically calculate their boiler water temp), instead of using little stick on strips in an effort to measure the housing temperature, etc.

The chart I have provided above is just what I see on a daily basis with regard to my La Pavoni; it measures pressure against the boiler water temperature.

I should probably play around with the adjustment on the pressure relief valve to see what sort of impact that has.

Anyway, if I'm missing something as far as tying the charts to figuring out the boiler temperature from the gauge pressure, I would like to know and understand that. So far, I'm not seeing it in the charts or the calculator.

Ray

I have more faith in physics than I have in the accuracy of your gauges/measurements.

There are factors at work here where the clean, theoretical readings from the charts will not match the here-and-now reality.

Case in point: there are timing factors in a dynamic physical system that practically cannot be reflected on any chart which assumes theoretical stasis. For example, as water in a chamber is heated, it makes perfect sense that just before that water boils at 212F, the pressure will still be at the one bar level, since no steam has been created yet to raise that pressure. After boiling for a period, the pressure will rise from the steam created as will the temperature of the super-heated water under that pressure. So far, so good.

But when the desired pressure is reached and the heat is shut off, the water will stop boiling and may cool at a different rate than the subsiding pressure would normally indicate. Or the opposite: if the pressure is released suddenly (e.g. from forcing water into the group) the water in the chamber will cool, but not fast enough to match the readings on any chart at that point in time. In a cycling system with pressure lags and other confounding factors such as these, we should not be surprised that actual behavior may not echo theoretical expectations.

I suspect that the short-cut that we Pavoni users are waiting for is being able to reliably know what the water temperature will be at the dispersion screen based on a quick look at the pressure gauge. But good luck with that: the temperature behavior of all that brass is going to fatally compromise any direct reading of boiler temperature or pressure in providing a standardized water temperature at the coffee. However, combining the temperature information with a standardized group-head temperature, as perhaps controlled via the usual combinations of timings, flushes and cooled portafilters - and measured by a heat strip for example - can stabilize our brew factors and thus our results.

So thanks Ray, and I look forward to seeing what's next.

allon wrote:I have more faith in physics than I have in the accuracy of your gauges/measurements.

I agree totally. I study physics and quantum mechanics myself. I have a background in electrical engineering. I'm not arguing with you on that point. Certainly, all this can be expressed mathematically, etc.

My question, however, is let's see you do it using the formulas.

So far, I haven't seen that.

Ray