Relationship between the pump’s self-priming height, allowable installation height, and allowable suction vacuum level
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I’ve never been able to figure out the difference between the self-priming height, the allowable installation height, and the allowable suction vacuum height
The allowable suction vacuum level is the lowest absolute pressure (expressed as a vacuum degree) at the pump’s inlet that prevents cavitation from occurring; it is expressed in terms of liquid column height and is known as the pump’s allowable suction vacuum level. The self-priming height is the difference in height between the liquid surface and the centerline of the pump inlet. The allowable installation height is the maximum height difference between the centerline of the pump inlet and the liquid surface, under which cavitation does not occur in the pump. Typically, pipeline losses and a 0.5-meter margin need to be considered.
Is the self-priming height the difference in height between the centerline of the pump inlet and the liquid surface, or the difference in height between the liquid surface and the highest point of the pump inlet pipeline? If the pump inlet pipeline has an inverted U-shaped bend, is the self-priming height the height difference from the liquid surface to the inverted U-shaped bend (N-shaped bend)?
It depends on whether the medium vaporizes upon reaching the top of the U-bend; if it vaporizes, self-priming will not be possible. If it does not vaporize, the self-priming height can be considered as the distance from the pump inlet to the liquid surface
Why use a full U-shaped bend at the inlet? The inlet of a self-priming pump should be as short as possible to reduce pipeline losses
The installation height of a pump refers to the vertical distance between the centerline of the pump shaft and the liquid level at the pump’s suction side. In actual calculations, it refers to the vertical distance between the top surface of the pump base and the liquid level at the suction side, and it is calculated using equation (3.0.4-3). How should this statement be understood? In HG20570-5, it relates to the calculation of the pump installation height Hg