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.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.
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)