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The Pressure Regulation Valve (OPV)
Now back to the pressure regulation valve. Think of it as a safety valve. Without it, using a blind filter would cause the pump to stall and overheat. Likewise for coffee that is too fine. The pressure regulation valve acts as a safety release and pops open when the set pressure is exceeded and diverts water back to the reservoir. Ideally the OPV should be set to 9bar, so no matter how fine your grind or how hard your tamp, the coffee will never see more than 9bar.
So with all that in mind – here’s the method to measure what pressure you Silvia will pump water through your grind.
Take off the water tank lid.
Separate the intake tube (the longer one) from the overflow tube (you guessed it . . the shorter one!) Hang the overflow tube over the side – we’ll be measuring water that comes out of this.
Insert a blind filter into your handle and lock her into the group head.
Hit your brew switch and let her groan under the full resistance that your pressure regulation valve is set at. Wait until water starts pouring out of the overflow tube.
Once it is a steady flow then start collecting it in a measuring cup and start a timer.
As soon as your timer gets to 30sec then pull the measuring cup away. Flick the brew switch to off.
Measure the amount of water you have collected (if you want to be precise then maybe weigh it with digital kitchen scales).
Double it to get your 60sec pour amount and look up the graph above until you get to the main curve and measure off the pressure. That is the pressure of resistance your pressure regulation valve is set at.