ECM Senior Member Joined: 11 Oct 2003 Posts: 338 Location: Burlington, Ontario Canada Expertise: I like coffee
Espresso: Giotto Premium + Cantesa... Grinder: Mazzer Robour E Vac Pot: French Press Drip: yes Roaster: Fresh Roast+8, i-roast and...
Posted Sat Mar 19, 2005, 12:52pm Subject: Help Me Adjust Overpressure Valve on a Giotto Premium
I am hoping you can help me.
I have a Giotto Premium which is set to 11bar at the factory. I have been trying to pull good shots now for five months and I have tried everything under the sun. Yes I home roast and I have a Mazzer Mini grinder. My shots tend to taste rather sharp, too bright for my taste. I would like to adjust the "overpressure valve" but I have no idea where it’s located. I would really appreciate some good close-up photos of the valve in a Giotto Premium and some well explained instructions on how to adjust it.
ECM Senior Member Joined: 11 Oct 2003 Posts: 338 Location: Burlington, Ontario Canada Expertise: I like coffee
Espresso: Giotto Premium + Cantesa... Grinder: Mazzer Robour E Vac Pot: French Press Drip: yes Roaster: Fresh Roast+8, i-roast and...
Posted Sat Mar 19, 2005, 2:21pm Subject: Re: Help Me Adjust Overpressure Valve on a Giotto Premium
Thank you Dan_Kehn:
I actually found out about this adjustment through these posts. However, the photo is of the switch itself and not it's location in the machine, (where the switch is in relation to its surroundings). I realize that the other thread has a diagram but I am looking for photos of the inside of a Giotto P with the "Overpressure Valve" clearly labeled.
I removed all the panels to take interior photographs as documentation. The three panels are each held by two 7mm bolts on the bottom that slide into slotted tabs (six total) and the upper corner attaches to the adjacent panel (or front of the machine). You can either (a) loosen the six bolts underneath and remove the two 7mm nuts holding the two side panels' front corners to the machine's faceplate, then remove the three panels still loosely attached to each other by their upper corners, or (b) remove only the back panel by loosening its two bottom bolts and then removing the two corner bolts. In both cases, you must first disconnect the wire to the low-water lead, remove the top (4 screws), and the water tank holder (2 screws). There's not a lot of clearance to access the inner bolts / nuts holding the panels on, so be careful not to scrape your knuckles.
Reminder: Unplug the machine before starting. Electrocution will ruin your weekend plans.
Does one have to remove some sort of plastic cap off the "Overpressure Valve" before you can adjust it?
The OPV is topped by a plastic elbow & brass fitting. Remove the silicone tubing that leads from it to the tank, and then remove the brass fitting and plastic elbow that caps the OPV (see image below).
How difficult is it to take apart these panels?
It's not easy, and quite difficult if you don't happen to have a 7mm box-end wrench. I was unable to manuever a pair of pliers or adjustable wrench in there. At least I finally got to use the teenie-tiny metric wrenches that had sat at the bottom of my toolbox for 20+ years. :-o
As a closing thought... unless you're pulling ristrettos, the setting of the OPV is irrelevant because the brew pressure is determined by the resistance of the puck or OPV setting, whichever is lower. At standard double-shot flow rates, your pump max's out at around 9 bar.
-- Dan
PS: I no longer have the Giotto Premium in-house. The above is from my memory and notes, so I can't be certain of the exact screw locations and bolt sizes. Corrections from current owners are welcome.
ECM Senior Member Joined: 11 Oct 2003 Posts: 338 Location: Burlington, Ontario Canada Expertise: I like coffee
Espresso: Giotto Premium + Cantesa... Grinder: Mazzer Robour E Vac Pot: French Press Drip: yes Roaster: Fresh Roast+8, i-roast and...
Posted Sat Mar 19, 2005, 8:30pm Subject: Re: Help Me Adjust Overpressure Valve on a Giotto Premium
Hey thanks again buddy!
Hello Again Dan_Kehn
Well after posting my questions to you I became increasingly curious and had to proceed myself. Boy you were right about those screws; they were a real hassle to get off. I opted to remove the top and back panels. Once inside the machine, I managed to actually unscrew the fitting in question without having to remove the tubing itself. It turns out that one can actually rotate the plastic end making it unnecessary to remove the plastic tubing from the fitting. Once I removed the fitting itself, I identified the slotted screw head as pictured in your helpful post. However, on my Giotto, the flat head notch was impeded somewhat by a raised metal portion right at the very center of the fitting. Very carefully, I managed to fit a small screwdriver in the notch and turned the valve about ¾ of a turn to the left. Originally the slot was facing the ten o-clock position. Once I readjusted the valve to the left it is now moved to the five o-cock position.
It was late by time I managed to put the!!!! thing back together so I couldn’t taste my adjustments. I do tend to lean toward ristrettos so I am hoping that tomorrow will bring a new taste sensation to my awaiting taste buds.
Posted Fri Jun 3, 2005, 7:12pm Subject: Re: Help Me Adjust Overpressure Valve on a Giotto Premium
Reminder: The OPV / expansion valve controls the maximum pressure, the coffee puck resistance generally determines the minimum. In your case, the expansion valve spring is relenting at 8.25 bar. According to Schomer, that's a pretty good brew pressure (and I agree). If, however, you want to raise it and the expansion valve shim is at the bottom of its travel, then adding a washer beneath the shim seems the next logical step.
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