What is the likely outcome if a centrifugal air blower is started with the discharge valve closed?

When a centrifugal air blower is started with the discharge valve closed, the system experiences a substantial restriction of airflow. Centrifugal blowers are designed to move a specific volume of air, and when the discharge is blocked, the blower cannot achieve its intended operating conditions. As a result, the pressure within the blower increases while the volume flow rate decreases significantly.

This situation leads to the operating drive motor drawing a higher than normal current, potentially exceeding the full load running current of the motor. The motor's protection systems may trigger if the current surpasses safe levels for an extended period, risking overheating or damage to the motor.

While the efficiency of the blower may indeed drop due to the improper operating condition, the immediate and critical concern is the increase in current draw. Therefore, starting with a closed discharge valve is markedly detrimental to the motor performance, showcasing the relationship between airflow resistance, pressure buildup, and motor current in centrifugal blower operations.