Self-priming height of the unloading pump
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I would like to ask the experts: Is the self-priming height of a discharge pump the vertical distance from the center line of the horizontal pipe extending from the top of the tank to the center line of the pump’s suction inlet? ? ? Waiting online
Is the lowest liquid level in the tank above or below the centerline of the pump shaft? If it is above, siphoning can occur as the fluid flows down from the top of the tank; if it is below, self-priming takes place
I think the self-priming height is related to the difference between the lowest liquid level and the height of the pump shaft’s centerline, as well as the pressure drop in the suction pipeline. However, a colleague from the pump manufacturing company said that the self-priming height is determined by the distance between the lowest liquid level and the highest point of the bend in the pump’s inlet pipeline. I don’t know who’s right and who’s wrong?
This post was last edited by foam_ZPTK on 2017-12-1 15:53. Just calculate the net positive suction head available for the device. NPSHa = Pc/ρg + Hg – Hc – Pv/ρg. Pc is the pressure at the liquid surface; Hg represents the backflow height, and it takes a negative value in the case of suction. Hc represents the pipeline loss; Pv is the vaporization pressure of the medium, ρ is the density of the medium, and g is the acceleration due to gravity (9.81). All values are calculated using absolute pressure. The frictional losses in the piping along a typical inlet are around 2 meters per 100 meters; the local losses caused by valves and filters can be added to this value. The liquid level is calculated based on the lowest scenario. If the liquid level is above the centerline Hg of the pump impeller, a positive value is taken; if it is below, a negative value is taken.
The self-priming height of a self-priming pump should be the vertical distance from the liquid surface to the pump’s inlet; however, the inlet pipe should not be too long, as this can affect the priming capability
The self-priming height, in my opinion, is the sum of the vertical distance from the lowest level of the liquid surface to the highest point of the dip pipe, and the horizontal distance between the dip pipe and the pump inlet. In a self-priming pump, the liquid first moves from the lowest level to the highest point of the dip pipe; thereafter, it flows downward by gravity, and then the pump’s suction force draws the liquid into the pump inlet