What is the cause when a mechanical blower keeps turning on and off due to high pressure?

When a mechanical blower repeatedly turns on and off due to high pressure, it often indicates that there's an obstruction or issue in the system that is causing a restriction to airflow. One common cause for this issue is valve closure downpipe. If a valve is closed or partially closed downstream of the blower, it will create a pressure buildup because the air has nowhere to go. This increase in pressure can trigger the blower's safety mechanisms to turn off to prevent damage, causing the on and off cycling of the blower.

On the other hand, issues such as blower motor failure, lack of power supply, or excessive airflow do not directly relate to a situation where the blower is cycling due to high pressure. Blower motor failure would more likely cause the blower not to operate at all, a lack of power supply would prevent the blower from starting, and excessive airflow is generally not associated with high pressure but rather implies the blower is effectively moving air. Thus, the presence of high pressure due to a valve closure downpipe is the most logical explanation for the observed behavior of the blower.