Roman,
I'm not sure you really grasped the nettle of what the other posts says as repeated by adam above.
Your gear pump at a fixed speed will try to flow virtually the same flow through it until it hits either the torque limit of the motor or excess power trip or the internal or external pressure relief limit.
How much flow you will get is dependent on these limits and the downstream system. A bigger pipe has, in general, less frictional resistance for the same flow rate. Your pump only sees the back pressure from the system. As the flow is essentially fixed, shaft power is proportional to pressure. Twice the pressure required to move the same flow, twice the shaft power required to do it.
does that make sense?
LI
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