HBchris wrote:For anyone that knows or can check, what is the flow rate (grams / sec) of various machines such as: vesuvius, Strada, Hydra MVP. when at 1 bar? 2 bar? 3 bar?
As I know pressure and flow are directly related. Lower pressure would result in lower flow.
Just curious to see how that compares to Slayer, which has a pre-brew flow rate (usually set between 1 - 2g per second).
I've never seen for these machines, a chart with pressure and flow rate profiles above the puck, where it counts eventually...
I imagine the flow rate as being dependent of the hydraulic resistance between the rotary pump output (constant pressure) and the atmospheric 0 bar pressure (gauge) as reference; among the flow restrictors on the circuit, the main one is the puck itself;
the puck resistance is the highest in the circuit and soon after wetting, it closes the chamber space (headspace, or the cylinder chamber) so the flow rate is the maximum above the puck - 0 bar phase; after a time interval, depending of the flow rate upstream, the volume is filled enough to have a pressure ramp until the (variable) puck resistance comes into play, as the puck becomes saturated;
from now on comes the brewing flow, and the flow rate depends on the puck resistance and the distribution of pressure fall among the restrictors on the water circuit;
please correct me, as this is my limited and simplified image of the process, considering my experiments with my modified Strega (dimmer, group heater PID-ed, PI pressure gauge); no experience with high end professional machines;
and btw, with hybrid, vibe pump machines, like Strega, pressure and flow rate are inversely related
so, i.e. after a 5s zero bar stage - puck soaking, of filling the cylinder chamber with the maximum pump flow rate of more than 10 ml/sec, follows a pressure ramp in which the flow rate from the pump is decreasing to less than 3 ml/sec as the OPV is opening, and the process enters next stage of spring pressure extraction; this variable flow rate stage could be beneficial for a smooth flow start through the puck; or at least for an added forgiveness...
full kind of variations follows: for ex., stop the pump when maximum pressure reached, and wait for a slower decrease in pressure until 4 bar (the saturated puck is permeable), then lift the lever on springs, but retaining the lever to maintain approx. the same flow rate; that would mean a slow PI, then a ramp to max pressure (kind of a spike), then decrease and approx. a steady low;