Issues regarding the net positive suction head of pumps

The larger it is, the less likely cavitation will occur; it seems it doesn’t cause any particular problems.

It must be chosen to be larger, equal to or greater than 0.5. Protection against cavitation in pumps.

It’s okay; the greater the net positive suction head, the less likely cavitation will occur.

If the net positive suction head is set too high, it becomes difficult to select a pump, and the price of the pump will increase

The effective NPSH is calculated based on the pump’s inlet piping system. Pump manufacturers design the pumps using this effective NPSH as well as the required NPSH; generally, it is such that \"Effective NPSH – Required NPSH > 0.6 m\"

The smaller NASHA is, the better the cavitation resistance of the pump, which is related to the pump itself and its operating conditions! Using NASHA allows one to determine the net positive suction head required for operating the pump; this value must be greater than the critical net positive suction head in order to prevent cavitation during pump operation! :handshake

This post was last edited by Uemaki on 2009-6-9 at 16:37. We have a Class A design institute that specifies in its requirements for pump selection that the net positive suction head required is “12.5/15 M”. I’m not quite sure what this means; could someone please explain it? :dizzy:

It should be noted that it has gone through three levels of review

When the pump is in operation, vapor is generated at the inlet of the impeller due to a certain vacuum pressure. The vaporized bubbles, driven by the impact of liquid particles, cause erosion on metal surfaces such as those of the impeller, thereby damaging them. This vacuum pressure is known as the vaporization pressure. The net positive suction head is the excess energy per unit weight of liquid at the pump’s inlet, above the vaporization pressure. The unit is indicated in meters, as (NPSH)r. The suction lift is equivalent to the required net positive suction head Δh: it represents the vacuum level at which the pump can draw in liquid, or in other words, the maximum installation height allowed for the pump, measured in meters.

The greater the effective net positive suction head of a pump, the less likely it is to suffer from cavitation； His determination corresponds to the pressure before the pump ； It is advisable for the effective NPSH of a pump to be greater than the required NPSH (provided by the manufacturer) by 1 m.

This post was last edited by zfy_80522 on 2009-6-11 21:03. NPSH: Refers to the difference between the total head of the liquid at the pump inlet and the pressure head required for the liquid to vaporize; it is expressed in meters (of water column) and denoted as (NPSH). It can be categorized as follows: NPSHa – also known as available NPSH; the higher this value, the less likely cavitation will occur； 　　 NPSHr —— pump net positive suction head, 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.