TroyR wrote:Thanks, $30 ish CAD at ColeParmer.ca for the gauge.
Actually, I have yet to convince myself that dialing down my OPV from 13 bar to anything else is a good idea (or at least that it will make a difference to most of my shots). I am of the mind that a good shot will naturally create a system pressure in the 8 or 9 bar range and that the 13 bar OPV is a max limit for the system to allow flow and prevent damage in the case of a choked system.
Anybody want to support that or change my mind?
Regards,
Troy
My experience is that much over 9 bars at the group makes the taste quite sharp and bitter, regardless of the pressure profile or pre-infusion scheme. I'm fortunate to have an electronically controlled pressure system that allows me to program brew pressures, profiles and pre-infusion while holding other variables constant. It is also by no means true that the system pressure will self-regulate to 9 bars if the flow is correct thru the cake. Pressure thru the cake is dependent on the upstream pressure established by the pump, the pump type, pressure relief valve configuration, and the configuration of the flow path between the pump and the group (diameter, length, gicleurs, solenoid location and type, etc.). The right way to do the measurement is to do it under flowing conditions. It's the only way you're gonna make any meaningful correlation to taste that can be transferred to other machinery. The 13 bar number that you quote may work as a static pressure measurement for a machine that uses a vibe pump with a long-stroke pressure relief valve, but it will not work at all for a machine with a short-stroke pressure relief valve scheme, or rotary pump. Best to do the measurement properly so that there is no performance variation due to flow path variability.
-Greg
