Why do we need to close the discharge or delivery valve of a centrifugal pump during start-up?
There is no place such as in Ammonia Process, Basic Process, Chemical Engineering, Chemical Process Technology, Chemical Industries, Lubricant Manufacturing, Manufacturing Industries, Oil and Gas, Petrochemicals, which did not use the centrifugal pump?
=> It is general practice to close the delivery valve of the centrifugal pump during start-up and it is highly recommended for the critical services where the liquid is at boiling/bubble point (Ex. Reflux pump of distillation column). The procedure is to close the valve and start the pump. After this open the discharge valve slowly till 100% which stabilizes the complete system. If this procedure is not followed and the valve is kept 100% open and the pump is started, NPSHa for this will be minimum because of losses due to acceleration during startup. This will result in cavitation of the pump.
=> To minimize the starting torque on the motor.
=> To load the delivery pipe network gradually if it is the only pump that feeds the network.
=> If it is a parallel-connected pump, this method will insure against any reverse flow due to malfunctioning of the upstream side check valve.
# There are some centrifugal pumps, called axial or propeller pumps, for which the delivery valve has to be kept open at a min. % as determined by the pump characteristics so, the reason for keeping the delivery valve in the minimum open condition is to minimize the starting torque imposed on the motor.
That’s Why do we need to close the discharge or delivery valve of a centrifugal pump during start-up?