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This post was last edited by 3983596_FPPZ on 2018-11-22 at 11:18. 1.jpg Regarding self-priming centrifugal pumps, which of the following statements are correct? (Multiple choice) A. Under standard atmospheric pressure, the ideal maximum priming height is 10.33 meters. B. A thinner inlet pipeline should be used; if the inlet pipeline is too thick, priming will not be possible. C. The priming time is related to the amount of air present in the inlet pipeline. D. The priming capacity is directly related to the NPSHr value, and has no direct relation to flow rate, head, or speed. Answers: ACD. A. Negative pressure priming relies on the difference between atmospheric pressure and absolute pressure (atmospheric pressure – absolute pressure = vacuum level); therefore, under ideal conditions, the maximum priming height is determined by the capacity provided by one unit of atmospheric pressure, which is 10.33 meters. For pumps, the thickness of the inlet pipe has no impact on suction power; therefore, the suction capacity remains the same regardless of the pipe’s thickness. What’s more, the small diameter of the pipe may lead to a high flow rate and significant losses, thereby reducing the self-priming capacity. The difference between thick and thin pipes lies solely in the thickness of the pipe; a thicker pipe results in a larger volume of air remaining in the tank, which requires a longer self-priming time. The principle and process of self-priming can be understood by imagining the external environment as a vacuum; in this case, atmospheric pressure drives the medium into the pump from the bottom of the inlet pipe. C Because the self-priming process involves moving the air in the inlet pipeline and within the pump into the outlet pipeline, an overly large or long inlet pipeline will inevitably increase the self-priming time. The self-priming capacity of pump D is directly related to the net positive suction head according to a formula; the greater the net positive suction head, the lower the self-priming height. For more details on this principle, see https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=2136578. Therefore, the answers are ACD