by Al deHyde on Mon Mar 21, 2011 7:05 pm
This may be more than what you're asking for, but here's my take:
When I received my Giotto (Evol, but same machine) it was cycling between a low of 0.83 and a high of 1.10. It made good espresso then. Based on some comments here, I raised the temp gradually through full turns of the pressurestat by 1, 2, 3 and 4 turns, leaving each at those settings for about a week.
A few weeks later, I reversed the process, going from +4 to +3 to +2, +1 and zero (original settings). I was surprised by that the readings going down were the same as going up (there is a lot of spring tension in the pressurestat, so I was not expecting such a result going in the opposite direction). I then went down to -1 turn and then -2 turns. The last gave my readings on my boiler pressure gauge of 0.80 and 1.01 bar (the low and high in the cycle).
In the end, I liked it right where the factory had it set, and I've left it there since. I was able to make good espresso at every setting, just the nature of the flush cycles changed, and the steam pressure changed a bit. Even at a setting of -2 on the pressurestat, there was plenty of steaming power to make good microfoam - I think it took a little longer is all. However, at the zero setting (the mfg original setting) all I need is a fairly short flush, grind my coffee and go. I use Eric's E61 thermometer as an indispensable tool for my flush, and as a check during extraction. It was useful using a Scace thermocouple initially, but once you get used to the temp differential between the E61 device inside the head, and the exit temperature onto the puck, it's duck soup.
A couple of comments is all:
Sirai Pressurestat - it's a slotted screw inside a plastic housing (yellow cap). I suggest you take a Sharpie pen and make a nice, permanent black dot on one side of the screw, so you can tell right away which side is which. You might also want to make another mark on the black plastic housing (a scratch, or a permanent silver sharpie) where the black dot on the screw lines up with the mark on the housing. Then keep a record of any changes you make.
Boiler Pressure Gauge - I don't have any idea how accurate these are, but I suspect there may well be some variation between individual gauges on factory machines. So the readings from my Giotto may be a little different than yours, but the boiler pressure may be the same. If they calibrate the Sirai pressurestat settings for their machines at the factory with a pressure gauge, it may be much more accurate (and expensive) than what is installed on the machines.
To sum, you might want to get used to using the machine at its factory setting because there just might be a reason they set these where they are (everyone's seems to be a little low like this). I rely totally on the E61 thermometer for my flushes - you can establish a regimen to get whatever 'average' output temp profile you want once you establish some baselines. Only after you have a feel for that, and have some idea what you're looking for and how to measure that would I go and change anything. Also, one vendor of these machines made it quite clear that mucking with the pressurestat on this machine would void the warranty (just fyi)
Marty
