Maciek,
I think something is wrong with your translation of the main drain pump:
"The drain performance by // and -- mode
are similar up to depth of 57 meters. At greater depth the performance by // mode decreases strongly. It is practical to switch to the - - mode at a depth of 50 meters. During trials, by connecting the auxiliary trim and drain pump (358 liters/minute) in
parallel, drain performance at depths greater than 50 meters is increased by 40%."
Correct would be something like this:
"The performance of // and -- mode
will cross on the graph at a depth of 57 meters. At greater depth the performance decreases strongly when operating in // mode. In practice you should switch to the -- mode at a depth of 50 meters. By the hook-up of the auxiliary trim and drain pump (358 liters/minute)
in serial to the suction and pressure lines of the main drain pump, the drain performance at depths greater than 50 meters was increased during trials by 40%"
But it's possible that I just don't understand it all all
Anyway "Praktisch ist ab … überzugehen" is clearly a directive.