Back to the discussion of the pressure adjustment on the new Silvia,
I believe the new overpressure valve has a nut on it (where outflow
hose that goes back to the water tank connects). This can be turned
to regulate the pressure at which the valve opens to relieve boiler
The best method of adjusting it would be to connect a pressure gauge
to the bottom of a portafilter, and adjust the nut to a reading of ~9
bar. (the stock silvia portafilter has a slot in it, which causes
leaks and makes this difficult).
I have the old style non-adjustable overpressure valve, which I made
adjustable with a lot of teflon tape and a homebrew soft, thin washer.
I have a pressure gauge, but I'm somewhat lazy and cheap, so I've
never bothered to get the fitting to hook it up to my portafilter.
Instead somewhere I found a suggestion (don't remember if it was here
or alt.coffee) to check the performance charts for the pump on the
Ulka website. From there I found the delivery rate of the pump at 9
bar (8.88 atm, 130 psi, 6750 torr, 900 kPa, et cetera), and adjusted
it until I got approximately that rate delivered out of the overflow
hose, with the blind filter basket installed.
Did it make a difference in the cup? I think so, but it could be
placebo effect. For what it cost me, it was certainly worth doing.
On 9/4/07, Tim Deines wrote: