Abe Carmeli wrote:My point is that fixing flow rate, as Greg has done here, may not be a good idea for that very same reason. Different shops use different flow rates for their extraction, and different pressure. Without an adjustable flow rate valve, this is becoming a problem. That is of course if you want to be precise within a tenth of a degree.

Different shops may use different flow rates, but the point is to provide a standardized methodology that remains consistent. If a shop wants to brew at 10 bars rather than 9, then the flow rate will be higher, but it will be constant to within a couple of percent for a constant brew pressure and reasonable amount of temperature variation. Dunno how much you've used it yet, but I think you'll find that espresso machines are way less reproducible than 10ths of a degree, even though the thermofilter has precision that is on that order. It's also important to realize that for an espresso machine to work well, the design is gonna have to be robust enough to be stable for more than 25 seconds +- 5. If it can't be stable for 30 then it won't reproduce temperatures in any duty cycle approaching continuous duty. So reproducibility seems to me to be more important than nailing a precise volumetric amount, as long as the volumetric flow rate falls within the standard for espresso.

Variability in flow rates is possible using needle valves, and I tried a bunch of em. There are very expensive, require pre-loaded stems to keep thread backlash from affecting flowrate, and less repeatable than the orifice, which behaves very repeatably. In my way of looking at the problem, repeatability was a more useful objective.

-Greg (If it's still off at 9 bars, lemme know and I'll change out the flowmeter for you)

Abe Carmeli wrote:It could also be coffee clogging the exit hole. Greg, how do you clean it and release a clog?

Bob will be the first one to clog up a filter if he has done so. Bob, was your machine clean?

Answer is to remove the orifice from the filter and flush it out. Look thru the hole at a light source to see if it's clear. Don't try running any wire thru it because it's really tiny. You should also flush out the filter. Water should easily flow through it.

I'll include the need for clean machinery in the instruction set. We hadn't plugged one up with the filter in place but there's always a first I guess.

-Greg

gscace wrote:Variability if flow rates is possible using needle valves, and I tried a bunch of em. There are very expensive, require pre-loaded stems to keep thread backlash from affecting flowrate, and less repeatable than the orifice, which behaves very repeatably. In my way of looking at the problem, repeatability was a more useful objective.

If flow rate is mostly controlled by the orifice diameter, perhaps you can modify the orifice size to fit pressure variation, and offer 3 options: 8.5; 9; 9.5 bars. That will give a coffee shop the ability to measure brew temp using their specific pressure environment. If it is more than just orifice size, it gets more complicated.

gscace wrote:It's a good idea at first blush and one that I've tried out. The problem is that the internal volume of the plumbing gets so large that the espresso machine dumps a bunch of water out into the thermofilter on startup, which doesn't reflect what's going on when brewing. So until I can get the internal volume down it's gonna be a temperature only device.
-Greg

Hi Greg,

I think the key may be that you don't need to measure temperature profile and pressure at the same time. You could, then, have an instant tube fitting coming out the bottom of the unit, and use a plug when you weren't measuring pressure.

Best,
David

Ah yes. Nice idea. Back to the basement I go. The basement is pretty fun these days. Not only are there a zillion parts for thermometers, but I have like 6 grinders in there, the Linea 2-group, an Astra Pro, and a Concept 2 ergometer. One of the grinders is a new conical burr Mazzer Kony. Hmmmm. I digress. This is the thermofilter thread. Thanks for the great idea!

gscace wrote:
Bob will be the first one to clog up a filter if he has done so. Bob, was your machine clean?

Answer is to remove the orifice from the filter and flush it out. Look thru the hole at a light source to see if it's clear. Don't try running any wire thru it because it's really tiny. You should also flush out the filter. Water should easily flow through it.

I'll include the need for clean machinery in the instruction set. We hadn't plugged one up with the filter in place but there's always a first I guess.

-Greg

The problem was, indeed, a clogged orifice. I cleaned the machine's group shower head and back-flushed several times before beginning the measurement sessions but didn't do an Urnex clean-out. By the end of the three hours, the flow rate went from 2.25 oz/25 seconds (as-received, brand new condition), down to 1.25 oz/25 seconds.

I tried putting the pf under running water to clean out the filter but the flow rate remained at 1.25 oz. Then, instead of removing the orifice, I took some 30 AWG (0.010 inches) silver-plated copperweld (copper-clad steel) wire and cleaned the orifice. This size is smaller than the orifice diameter and after that all went back to normal: from 1.25 oz. before the cleaning to the original 2.25 oz immediately afterwards.

Problem solved. But what about those who don't do these measurements with a squeaky clean machine? I guess the planned info sheet including something about the device's sensitivity to clogging will be very helpful.

BobY

gscace wrote:The problem is that the internal volume of the plumbing gets so large that the espresso machine dumps a bunch of water out into the thermofilter on startup, which doesn't reflect what's going on when brewing.

how about using a capillary tube for the pressure gauge hookup?

BobY wrote: and brass-colored metal "filter material" inserted in the pipe,

whoo-hooo!



--barry "my contribution"

BobY wrote: Problem solved. But what about those who don't do these measurements with a squeaky clean machine? I guess the planned info sheet including something about the device's sensitivity to clogging will be very helpful.

it should not be necessary to use a squeaky clean machine. the filter in there should trap just about anything that isn't dissolved.

i wonder if there's an issue with material precipitating out on the orifice rim.

The problem was solved by inserting a fine gauge (30 AWG) wire into the orifice without any cleaning of the filter. Then yesterday, after a machine cleaning with Urnex and a soak of the pf sans end cap (orifice) I started again. I got about 30 straight shots with a flowrate of 70 ml/25 sec.

Then, inexplicably, the flowrate suddenly dropped to 60 for a couple of shots. I inserted the wire and once again. another few dozen 70 ml shots (dead nuts every single time). I'm not sure what could be precipitating. The water here is very (too) soft, and in the years that I have done occasional descalings of Silvia and, for the last year, the Andreja, I've never seen a single hint of scale.

It could be that a grain of coffee or something else was freed up from the filter and drifted down to the orifice. But when there is no obstruction, the device is working like a laboratory instrument; as close to perfect as I would ever need.

BobY