And that would indicate that backing off on the pressure decreases the turbulance in the potafilter. Higher pressure , increasing turbulance, or, a pattern of movement "within" the portafilter vice "through" the portafilter. Perhaps the decrease in pressure allows gravity to have a higher impact which adds to throughput. I'm learning a lot in this thread. Good stuff!

clynch wrote:And that would indicate that backing off on the pressure decreases the turbulance in the potafilter. Higher pressure , increasing turbulance, or, a pattern of movement "within" the portafilter vice "through" the portafilter.

Please describe what you mean by "turbulence in the portafilter" ? What do you think is going on there?

clynch wrote:Higher pressure , increasing turbulance, or, a pattern of movement "within" the portafilter vice "through" the portafilter. Perhaps the decrease in pressure allows gravity to have a higher impact which adds to throughput.

I think that is way overcomplicated. Rather, imagine a bed of small pebbles with space around them for water to flow. If you push harder the pebbles will be forced closer together making less space for the liquid to flow through. Less pressure allows for more space between pebbles and thus greater flow.

I can buy that ... and it makes more sense.

tekomino wrote:Rather, imagine a bed of small pebbles with space around them for water to flow. If you push harder the pebbles will be forced closer together making less space for the liquid to flow through. Less pressure allows for more space between pebbles and thus greater flow.

+1

Another reason given tends to be the migration of fines. The higher the pressure the more migration of fines to the bottom layers of the puck, resulting in greater resistance.

I have both a spring-loaded lever (La Riviera) and a completely manual drive (La Pavoni) and I much prefer the hands-on performance of the Pavoni. I LOVE the look of the Riviera. The aesthetics and solid construction are beautiful. But the spring-loaded piston just requires too much consistency and precision of grind, roast, and bean for my taste....variables that can be easily compensated for with an all-manual lever. I guess, what it comes down to is that I'm simply a control freak and prefer to have control over variables that the all-manual machine offers.

Anybody want to trade a Cremina for my La Riviera?