Cavitation and avoidance of the phenomenon

Σπηλαίωση και αποφυγή φαινομένου

Cavitation occurs in a pump when the pressure on the suction side of the pump is lower than the vapor pressure of the liquid. In this situation, small bubbles form in the water. These bubbles when bursting create a shock wave ( Shock Wave ) which results in damage mainly to the metal parts of the pump such as impellers, shaft etc. (Fig. 2.2.9 & 2.2.10)

Stainless steel as a material is more durable than brass and brass is more durable than cast iron in terms of cavitation.

The cavitation phenomenon also affects the performance of a pump, reducing its flow rate and its manometer.

Σπηλαίωση και αποφυγή φαινομένου
Σπηλαίωση και αποφυγή φαινομένου

Damage to the metal parts of the pump is only visible when disassembling the pump.
To avoid the phenomenon of cavitation
By solving the equation below, the maximum allowable suction depth for a pump or the required preload pressure needed for a pump to work properly can be calculated.

hmax = Hb – Hf – NPSH – Hv – Hs

hmax  : Maximum suction head, if negative it means that a preload pressure is required for the pump.

Ηb = Atmospheric pressure at the pump site (open circuit systems)

Hf : Friction loss in the suction pipe.

NPSH : Net Positive Suction Head (given by the pump manufacturer).

HV : Vapour pressure of the liquid

Hs : Safety factor

It is advisable that the above calculation is done by an engineer of the company that supplied your pump.

Our company, through the planning, study and design it undertakes, can help you choose the most suitable pump for the needs of your application.

Source: GRUNDFOS/PUMPHANDBOOK
Cavitation and NPSH
Cavitation occurs somewhere in a pump when the pressure is lower than the vapour pressure of the liquid, see figures 2.2.9 and 2.2.10

PUBLISHED: 30/03/2023

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