GCAP Operator 2 Practice Exam

The suggested minimum height of Net Positive Suction Head (NPSH) needed for gravity supply to a liquid ammonia pump is typically established to ensure that the pump has adequate suction to operate efficiently and avoid cavitation.

A height of 4 feet is generally regarded as sufficient to provide the necessary pressure at the pump inlet when dealing with liquid ammonia, which can have special handling and flow characteristics due to its low boiling point and potential for vaporization. The 4-foot minimum helps ensure that enough positive pressure is maintained at the pump intake to keep the ammonia in liquid form, especially when there might be variations in the system pressure or temperature.

This minimum height accounts for losses due to friction and other factors that might affect the pump's ability to draw in the liquid effectively from a gravitational supply. It's important to note that while some systems may operate safely with slightly less or more height, 4 feet is a standard benchmark within industry practices for safely delivering liquid ammonia to the pump without encountering vapor lock or cavitation issues.