Any operational issues that come to mind regarding the closed-loop water system mentioned earlier?

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Earlier, a member mentioned a closed-loop water circulation system, where the inlet and outlet pressures of the circulation pump are 0.33 and 0.6 MPa respectively. How are these inlet and outlet pressures generated? Is it generated by the water pump, or is there some kind of pressure-regulating valve in the circulation system to control it? I think this problem is very different from common open systems. In a split-system, the return water pressure (at the outlet of the pipeline) is always equal to atmospheric pressure, and the pressure at the pump outlet represents the actual head. However, the static head in a closed system is 0, so the pressure difference between the pump inlet and outlet is the pressure drop in the system piping. However, in a steady state, the pressures at the pump’s inlet and outlet are not constant; I believe this is related to the startup process. At startup, the outlet pressure of the pump is high, which results in a high return water pressure. How do fellow marine engineers calculate the inlet and outlet pressures of a pump at steady state? During operation, if the valves in the pipeline are closed, how do the inlet and outlet pressures of the pump change? For example, by increasing the rotational speed and thus the flow rate (with the pipeline remaining unchanged), how do the pressures at the inlet and outlet of the pump change?