The NPSH problem
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This post was last edited by FLYTOINTER on 2010-7-14 at 12:26. I would like to ask about the NPSH of pumps – what is the difference between NPSH and NPSHR, and what are their respective uses? Thank you
NPSHa —— the net positive suction head available of a device, also known as the effective net positive suction head; the higher this value, the less likely cavitation will occur； NPSHa = Ps/ρg + Vs/2g – Pc/ρg = Pc/ρg ± hg – hc – Ps/ρg. NPSHr is the pump’s net positive suction head; it is also known as the required net positive suction head or the dynamic pressure drop at the pump inlet. The lower this value, the better the pump’s resistance to cavitation ； NPSHc —— Critical net positive suction head, refers to the net positive suction head at which the pump’s performance declines by a certain amount ； ——The allowable NPSH is the NPSH used to determine the operating conditions of a pump, and it is usually taken as = (1.1～1.5) NPSHc. The conditions under which cavitation occurs in a pump are determined by both the pump itself and the suction setup. Therefore, to study the conditions under which cavitation occurs, it is necessary to consider both the pump itself and the suction system. The basic relationship for pump cavitation is NPSHc ≤ NPSHr ≤ NPSHa. NPSHa = NPSHr / (NPSHc) – this is the point at which cavitation begins in the pump; when NPSHa > NPSHr / (NPSHc), there is no cavitation in the pump. Last edited by lbp on 2009-4-7 17:51