[sparkycuda]

Closed systems (like equipment hydraulics) use positive displacement pumps such as gear and piston types. Positive displacement means when the pump turns, fluid is moved, without much power loss, due to the tight fitment of internal parts. Pressure relief valves are required to prevent over-pressure and pump damage.
Water pumps are typically non-positive displacement pumps, using an open impeller, that is not very efficient for high pressures, and don't use pressure regulating valves. Impeller pumps usually cannot be modified to increase pressure output very much. Even if you do get the pressure you want from this pump, as the system works at its upper pressure limits, you will increase heat buildup because of the fluid "slippage" (low efficiency) of impeller pumps.
If you want higher pressures, I'd recommend considering a gear-type pump designed for hydraulics.

Ken