What is one major reason why it is important to vent all air out of the seal housing?

Venting all air out of the seal housing is crucial primarily to prevent vapor locking. When air is trapped in the seal housing, it can create vapor pockets that interfere with the normal operation of the pump. Vapor locking occurs when these vapor pockets prevent liquid from flowing freely, leading to reduced efficiency and potential pump failure. By properly venting the seal housing, you ensure that the pump is filled with liquid rather than air, allowing it to operate at its designed capacity without interruptions caused by vapor. This practice is essential for maintaining the reliability and performance of pumps in various applications, especially those handling liquids at elevated temperatures or pressures where vapor formation is more likely.