When starting the pump, it is generally recommended to close the outlet valve. This is because closing the valve will prevent backflow or excess pressure from causing damage to the pump or other equipment in the system. Additionally, closing the outlet valve can help to prime the pump by building up pressure and forcing the fluid to start flowing through the pump. It is important to follow the manufacturer's instructions and any applicable safety guidelines when starting up a pump to ensure efficient and safe operation. By taking proper precautions and following best practices, pump operators can ensure smooth and reliable performance and avoid unnecessary downtime or repairs.