Boiler pressure gauges vs thermometers - Page 2

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pizzigri
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#11: Post by pizzigri »

homeburrero wrote:In a way that's true. What is actually being affected by the barometric pressure is the gauge (and the pressurestat.) They are both measuring the difference between atmospheric and boiler pressure.
OK, I get it now. The crappy manometer used in these machines are not absolute pressure gauges! And neither are the pstats. And neither the OPV, now that I think of it.

OldNuc
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#12: Post by OldNuc »

homeburrero wrote:In a way that's true. What is actually being affected by the barometric pressure is the gauge (and the pressurestat.) They are both measuring the difference between atmospheric and boiler pressure.
It is the little mentioned fact the both the gauge and prersurestat are differential pressure instruments, not absolute pressure instruments. Understanding and compensating for altitude changes is easier to understand by using temperature as the true boiler pressure is easily derived.

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Chert
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#13: Post by Chert »

pizzigri wrote:So, the temperature inside the boiler is actually more important than the actual pressure inside?"
.

Yes, I think so, because the temperature of the water as it mixes with the coffee is a very important determinant of flavor in the cup. If atmospheric pressure causes the boiler temperature to be cooler than accustomed to and I pull my shot at the group temperature that works at sea level, then the extraction temperature will be less.
LMWDP #198

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pizzigri
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#14: Post by pizzigri »

Sorry, I was rather reasoning that the temperature at the group was important - if there was a temperature to measure that is - that is the meaning of my reply.

jonr
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#15: Post by jonr »

I was rather reasoning that the temperature at the group was important
On my Europiccola that is true. The boiler temperature is pretty much a constant and the group temperature varies significantly. So the latter is all I need to measure.

OldNuc
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#16: Post by OldNuc »

The boiler water temperature is more or less a constant as long as the altitude the machine is operated at is constant.

Cmtwgr
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#17: Post by Cmtwgr »

One could ad a thermoprobe from the underside of the machine
then have a small plug to attach the meter to it when wanted ,
or just make it wireless ;o)
there is some room inside the machine

rip out the guts of a wireless grill thermometer , and you can sit in your living room and watch the temp of the machine in the kitchen ;o)
i have actually used a wireless thermometer during as descale , i did let the machine get up in temp , and turned it of , then sitting in the living room followed the drop in temp , then from time to time i did for at short time let the machine heat up

Ps the plugs for the sight glass , i think they are made out of brass, easy to machine

Copper isnt so bad to machine , it just takes sharp tools , the problem is it being soft , so difficult to hold without deforming it

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rpavlis (original poster)
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#18: Post by rpavlis (original poster) »

A wireless under the machine thermometer would really be great addition. One could indeed see the temperature whilst in another room. It would also be completely unobtrusive. Boiler temperature is normally fixed once the machines are warmed up, but one needs to be able to check it from time to time, and it is convenient during operation to follow heating progress.

It is too bad that manufacturers do not make some sort of thermometer well on groups to enable very accurate temperature determination there. This would be much better (and simpler) than attaching temperature probes. It would also be dramatically less obtrusive.

jonr
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#19: Post by jonr »

I have a spot of masking tape on the side of my group and then I use an IR thermometer. Works well and is less obtrusive, but is also less convenient for frequent checks. All exterior temperature measurements suffer from some inaccuracy caused by room temperature variations (would be interesting to measure exactly how much).

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drgary
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#20: Post by drgary »

This conversation is often encountered on H-B. Some very smart people are discussing how to measure with greater precision. And Franco's asking where that precision is needed in practical terms.
pizzigri wrote:I got the impression, reading this forum, that the boiler temperature is rather superfluous information, while the group temperature is a lot more important.
Since this thread is in the Levers forum I'll focus on that context.

Franco's question and his and others' follow-ups suggest three concerns:

1. How might measurement of boiler temperature assist brewing?

My best machine for learning this was a second generation, two-switch Europiccola. I controlled that by toggling power On/Off while watching the manometer and group thermometer. Some coffees pulled well within a wide temperature range at the group. Others, especially darker roasts, did well if I limited the top end of group temperature by toggling off before the pull. Sometimes I raised group temperature gradually to prevent overshoot, using half pumps and keeping boiler pressure relatively low. So, knowing boiler temperature helped me control group temperature to optimize shots. It was a manual process assisted by measurement.

2. How precise is sufficient?

Using the technique just described, for my purposes, a manometer and group thermometer were sufficient. But there's an implicit issue that's not been mentioned so far.

3. Accurate measurements help us guide each other. If two of us are trying a coffee by the same roaster, knowing accurate boiler pressure or more accurate temperature of the boiler and group helps to describe things more precisely. Or even with different coffees, it helps to know precise measurements if I'm describing how I pull a Nordic roast versus a full city+ roast. Being able to put that into words will help someone else.

Communicating this level of boiler temperature accuracy isn't necessary if the person dialing in their machine understands how to adjust flow rate with their grinder and adjust temperature, dose and grind by taste.
Gary
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What I WOULD do for a good cup of coffee!