Controlling brew pressure with E61 flow control device vs. OPV?

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#1: Post by mycatsnameisbernie »

Both of my E61 machines with Flow Control devices have their overpressure (aka bypass) valves set to 10 bar by their respective dealers. Both dealers say they do this to achieve a brew pressure of 9 bar. However, I can see on both machine's group pressure gauges that the brew pressure often reaches 10 bar, especially if I grind finer for a ristretto or slow extraction.

Would there be any difference in extraction if I use the Flow Control valve to limit pressure to 9 bar (or lower) vs. adjusting the OPV lower? To achieve 9 bar with the FC devices, I need to open them only a small amount, around 1/4 turn, so the flow rate is very low. If I were to lower the pressure with the OPV and keep the FC valve fully open, would I get a faster flow, or would the flow be limited by the rate water flows through the puck?

I noticed that 1st-Line's description of the Lelit Bianca says they deliberately set the Bianca's OPV to 11 bar, and recommend lower pressures be obtained by using the FC paddle. So they seem to imply there is no difference.

Can someone with a better knowledge of fluid dynamics than I have advise me if I should bother lowering my OPV, or just stick with the FC device to achieve 9 bar or lower?

Thanks for the help!

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#2: Post by cafeIKE »

Depends on the pressure pick off location. Typically e61 brew pressure gauges are pre gicleur. 10 on the gauge can be 8.5 on the puck.

The group gauge on the Bianca should match the pressure gauge when there is no flow with a blind basket and be lower with espresso being pulled.

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#3: Post by another_jim »

If the pressure gauge in the group, above the puck, says 8 bar, for instance; what difference can there possibly be if the OPV drops it to 9 and the flow control an extra bar to 8, or if the OPV drops it to 11, and the flow control the extra 3 bar to 8? Do you think the puck can tell the difference.

The lower you set the OPV, the lower the maximum pressure you can get at the flow control. But the more fine control you get. So set it get the highest pressure you ever intend to use, reading at the group gauge.
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