How far can positive displacement pumps self-prime under perfect conditions?

Positive displacement pumps are capable of self-priming due to their design, where they move fluid by trapping a fixed amount of liquid and then displacing that liquid into the pipeline. The height to which these pumps can self-prime is influenced by several factors, including the vapor pressure of the liquid being pumped and the environmental conditions.

Under perfect conditions, a positive displacement pump can theoretically self-prime up to approximately 8 meters (or about 26 feet). This is based on the principle that the maximum height from which water can be drawn is determined by atmospheric pressure at sea level, which exerts a force sufficient to lift water approximately this height. Various factors in real applications, such as friction losses and the characteristics of the fluid being moved, can affect this ideal self-priming height, but under optimal circumstances, the 8-meter figure is the accepted limit for many standards in the industry.

Therefore, the correct answer aligns with the understanding of the operating principles and practical capabilities of positive displacement pumps within ideal circumstances.