What is the minimum distance a header must be above the Normal Operating Water Level (NOWL) to prevent priming?

The minimum distance a header must be above the Normal Operating Water Level (NOWL) to prevent priming is 24 inches. Priming is a condition that occurs in steam systems when water is carried over with steam, which can lead to issues in performance and equipment damage. By maintaining a distance of at least 24 inches above the NOWL, the design ensures that steam can be captured effectively without the risk of water entering the steam lines. This distance facilitates adequate separation between the boiling water and the steam, which is essential in preventing carryover and ensuring smooth system operation.