Why when faucet is turned on pump turns off?

When the faucet is turned on, it creates a demand for water flow, which activates the pressure switch connected to the pump. This switch senses the drop in pressure in the system due to water being drawn and typically turns off the pump to prevent the system from becoming over-pressurized or to maintain a steady flow rate. If the pump continues to run while water is being drawn, it could lead to issues such as water hammer or damage to the Plumbing system. Thus, the pump operates in response to the pressure changes in the system.