I really want to get my brain around this OPV thing. It isn't making sense to me.
If, as I understand, it redirects the water when the pressure reaches a certain point. By preventing higher pressures it might lead to better pump life.
let me think this through. Extraction is related to surface area (which itself is related to weight of coffee and grind size). Water volume (this is flow rate through the puck) is related to resistance and pressure. Temperature is related to the temperature of water entering the brew chamber and the thermal mass of the group (which is related to material weight, thermal properties of the metal and group temp at the time of extraction).
If you have a valve that limits the top pressure value applied to the puck, it would mostly come into play when you grind too finely or tamp too hard. If you grind too coarsely or tamp weakly, pressure would never reachthe point where the OPV would come into play. OTOH if grind is too fine or tamped with too much pressure, more volume would be diverted back into the tank and it would take longer to get the same volume of espresso. Would it be over extracted because longer contact time? If you cut off the water at the usual time would itbe underextracted because of less volume? or do the effects of contact time and volume just cancel each other out? Are there too many variables to balance and having pressure steady just eliminates one of them?