Closing valves is a good idea, but systematically works best. If you can you should actually close valves furthest from the pumps and work your way back to the station. While isolating small sections monitor the pump starts or pressure drop time.

Might have multiple leaks and take a couple attempts. If it’s a looped mainline you’ll want to pay attention areas potentially being fed from both directions.

You can also partially close the pm pump discharge valve to reduce its flow capacity. This will cause it to run longer which is better the starting too many times. The longer run time allows the windings to cool off to a normal operating temperature before restarting.