one of the reasons i delayed so long about adding the A'sump ( i have the 2 quart one in my SPF's engine compartment) is because i was worried that it would "steal"
oil from the engine when the accusump refilled.
But in discussing with the Canton folks, the return valve is restricted, so while it can dump the
oil plenty fast, it is slower on the return inlet flow back into the A'sump. I have not noted any delay in running my engine back up and watching the
oil pressure gage on the engine, even when the A'sump is refilling at the same time. My guess is that the oil pressure bypass spring in the oil pump notes the lessened oil flow resistance, and simply momentarily pumps more oil to both the engine and the A'sump.
I toggle the A'sump with the engine off, then suck it all out via the dipstick tube, then add a crankcase's worth of oil, start the engine, turn the sump off, which still allows it to fill with an electrical valve (the electric valve is one way only, it only discharges the oil, the sump will always accept any oil pressure from the engine, if the sump has less oil pressure than whatever the engine is putting out. )
Then re-check the dipstick, and add about a quart and a half, to bring it up to full with the A'sump also filled and ready for the next cold start.
Interestingly, if you have the electric valve, you cannot just turn the switch on, dump the oil into the system, then turn it off, and have that oil stay in the motor. It will go right back to the A'sump as soon as the oil pressure rises. The one way return valve is always open on the electric valve.
Keeps folks from running around with an overfull crankcase if they turn the valve off and drive around.