Thanks for technically detailed answer.
So theoratically using softer spring may increase the performance ?
And how about using smaller pulley? (i do not feel any difference at higher RPMs. 600 vs 3000 rpm. . Should i ?)
Yes, no, maybe, possibly but that depends on what or how you are defining performance.
The pump can only pump to the head allowed by the RPM
Pressure is determined by resistance to the flow ( cumulative back pressure)
The control valve has a minimum pressure
Once open its basic hydraulics- fluid moves piston and transmits both ways.
So what part of that are you wanting to alter?