Quarter turn pump adjustment makes world of difference

[zaphod]

So my drinks were crap... bitter and sourish. The naked filter revealed streaks of dark and light versus the caramel colored tones of a delicious shot. I replenished my beans, I played with the grind and dose and it was still ugly. I then plugged in the portafilter pressure gauge and threw the switch. The pressure ramped up to 7bar and then slowly crept to 8 and then 9. I adjusted the rotary pump pressure by a quarter turn and the range is between 8 and 10 with 9bar at the midway point ~ 12 seconds.

The caramel is back and the shots are sweet again. oh rapture.

[PureArabica]

Whatever works... right?
nick

[peterL]

I had similar success adjusting the overpressure valve on my vibe pump Cimbali Jr. I was having a lot of problems with channeling using the naked portafilter, but after adjustment, there was a huge improvement and no more channeling!

When the overpressure valve is adjusted properly, it leaks out a steady stream of water during a pull, so I guess that's why most prosumer machines have them closed - they would fill up the drip tray if there was no drain.