Basically cetrifugal pumps are "constant" pressure pumps whereby the discharge pressure, based on a fixed inlet pressure only varies a small amouunt for quite a wide variety of flow. Search on "pump curve" on this forum to see what I mean.
Positive Displacement Pumps (piston, screw, diapharm etc) are essentially "constant" flow pumps whereby the flowrate only vares a small amount for quite a wide variaiton in outlet pressure.
Centrifugal pumps work on differential head so if the inlet pressure goes up, the discharge head goes up by a simialr amount for the same flowrate.
If you posted the data sheet we might be able to help you a bit more, but I hope this gives you something to work with as it's a pretty vague question at the moment.
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