erics wrote:Espresso machine pumps would be classified as positive displacement pumps, most definitely NOT best started with the shut-off valve closed. To the best of my knowledge, all positive displacement pumps have some sort of protection (OPV, by-pass valve, relief valve, etc.) to account for this condition.
OPVs & by-pass valves are on the vibratory pumps cuz they push out like 15bars and are not adjustable, adjusting is done with OPVs.
There is no protection on HX lines or groupheads, double boilers, the brewboiler does not have a protection valve(and if they did they would be set above 9 bars).
On a regular startup in a brew there will be that 9bar pressure and basically NO water flowing anywhere for sometime before the water finds it way through the puck, and even then, we are talkin espressos here, there is so little water coming through, the pump is always pushing full on(unless you do a cooling flush...
Have anyone tried varying the power to their rotary motors and by doing so, being able to adjust the pumps flow?
My guess is that it will not run at all after a powerdrop.?