Why you have to close the exit valve before turn on the pump?

Closing the exit valve before turning on the pump is crucial to prevent backflow and ensure that the system builds up the necessary pressure. If the exit valve is open, the pump may not be able to create adequate pressure for proper operation, potentially leading to pump damage or inefficiency. Additionally, it helps to avoid cavitation, which can occur when the pump draws in air instead of liquid. Overall, this practice ensures safe and efficient pump operation.