Posted Sat Aug 7, 2004, 8:29pm Subject: How to adjust the brew pressure of a Giotto Premium?
Any Giotto owners adjusted the brew pressure of their machine? Below is what I believe is the expansion valve, but it doesn't appear to be adjustable. I am measuring 11 bar with a portafilter pressure gauge. There's no built-in gauge to measure during the pull itself, but the shots taste slightly overextracted and I would like to reduce the pressure a little to smooth them out. Am I overlooking something?
Ian Moderator Joined: 21 Jan 2003 Posts: 1,495 Location: England
Espresso: Euro2000,Rancilio Grinder: Mazzer,La Cimbali Vac Pot: Cona-->CraigA Drip: Belgique for emergencies Roaster: Primas with variac
Posted Sun Aug 8, 2004, 1:00am Subject: Re: How to adjust the brew pressure of a Giotto Premium?
If you take the valve apart there may be a shim (washer) that you can remove to reduce spring pressure - that's a common method of adjustment in hydraulics. Alternatively, you could fit a weaker spring or install an extra washer in the body which would also reduce the spring tension.
Posted Sun Aug 8, 2004, 4:55pm Subject: Re: How to adjust the brew pressure of a Giotto Premium?
Thanks Ian! (thinking out loud)... and yet there's something that doesn't sound right. Howard (easyrotor) reports the Salvatore has no means of adjusting its brew pressure other than changing the grind (link), the Giotto Premium and Livia 90 (link) apparently have limited means. This wouldn't be too inconvenient if either of these costly machines had brew pressure gauges, which leads me to wonder...
Is the message from these manufacturers essentially, "ignore the brew pressure -- it doesn't matter if it is 8.0 bar or 11 bar"?
The old line Italian firms never worried much about vibe pump pressure on home machines. Presumably they figured that the coffee and grinder being used wouldn't be too good, and if the pour volume/timing was in the ballpark, the pressure would be too. Even the Cimbali Juniors, which did come with adjustable pressure relief, were set to 15 bar from the plant. In bars, the tech would set it down and plumb the drip tray or reroute it back to the tank (for pourovers).
Italian roasters have bulletins that specify the temperature and pressure they want on each commercial machine model for their blends (Jolly's is somewhere on their site, but I can't find it anymore); so they take a lot more pains with the commercial market than they do the home market. But there really is no home espresso geek culture in Italy like in many other places; for instance, we don't have any Italians posting here, and I'm not aware of any Italian language ngs or forums for home espresso (there are some in almost every other language). So I don't believe they are aware of how their small one group machines are being used almost everywhere else in the world.
That would explain why some Italian machines are not easily regulated. But Salvatore's machine is made in the USA and they certainly spared little expense choosing components. So why would they omit an expansion valve? I can't think of a disadvantage of installing one (well, other than cost and filling the driptray faster for plumbed units).
Posted Mon Aug 9, 2004, 5:17am Subject: Re: How to adjust the brew pressure of a Giotto Premium?
Yes, commercial machines have a brew pressure adjustment. They usually have rotary pumps, which have a much greater flow rate than vibratory pumps, so they're capable of running multiple groups. Most are regulated to between 10 and 8 bar.
PS: Chas Rimpo's S1 website has a good picture of this adjustment, labeled F in Picture 2.
Posted Fri Oct 8, 2004, 5:31pm Subject: How to adjust the brew pressure of a Giotto Premium
FYI for future Giotto owners... I took the top off Giotto's expansion valve and indeed it does adjust (below left). Stick a small screwdriver blade in one of the slots and push the retention washer counter-clockwise to reduce the brew pressure. It was originally set to 11 bar and about 3/4 turn reduced it to 9 bar.
Posted Fri Oct 8, 2004, 5:38pm Subject: Re: How to adjust the brew pressure of a Giotto Premium?
While I was there, I added an external brew pressure gauge. The size of the exit tubing was conveniently 1/4" OD, so I was able to splice in a John Guest push-in tee. It took longer to get off the covers than add the gauge (six screws for the top, six 7mm bolts for the bottom casing, two 7mm hard-to-reach nuts for the front of the casing).
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