I’ve been doing some more maintenance on the Gaggia Classic. When I got it back from NY it was a bit choked what with the mineral deposits from that hard Catskill aqueduct water. So I disassembled it (photos here) but the one tiny port that I somehow didn’t read up on (or take apart and clean) was the 3-way solenoid valve (it requires a large wrench and possibly you’ll need to screw the 3-way solenoid into a piece of wood to get leverage on it, read Steven Heaton’s post here and Christopher Reed’s here).
Similarly, on the OPV valve (which I did disassemble, more info on that at Ruiz’s blog), I potentially over tightened the “over pressure” spring adjustment. So between the two (one likely blockage in the solenoid and too high of ‘over pressure’) I was getting some wonky behavior: occasional air-locks, high pressure into the puck, inability to clean by backflushing Cafiza.
Without a pressure gauge hooked up to a threaded portafilter all my “pressure adjustments” have been blind, however this time I did try and hit the recommended “over pressure flow rate” which is in the neighborhood of 130 ml for 30 seconds (using a blank basket). It does take a few adjustments to get it right, and I imagine if I put an actual gauge on it (which might be possible using a Presta valved bicycle inner tube and an actual bicycle pressure gauge) it’ll need to be adjusted further (10 Bars static, 9 Bars dynamic being the goal). My existing portafilter just has two spouts and is not threaded in the middle and I’d rather not splurge and spend another $50 for a portafilter I’m only going to use once, apparently there are a few floating around as loaners, so if you’re a Gaggia Users’ Group member and have one I’d be happy to pay a deposit and shipping to at least get the machine’s pressure set.