The most complete summary about pump cavitation
What is cavitation?
When the partial pressure of the liquid in the pump drops to a critical pressure, bubbles will be generated in the liquid. Cavitation is the whole process of bubble gathering, movement, splitting and elimination. The critical pressure is generally close to the vaporization pressure.
What are the hazards of cavitation?
01. Corrosion of overcurrent parts
There are two reasons for corrosion:
One is due to the high frequency (600~25000HZ) impact generated when the bubble bursts, and the pressure is as high as 49Mpa, resulting in mechanical erosion of the metal surface;
The second reason is that heat is released during vaporization and hydrolysis is generated by the action of the thermoelectric battery. The oxygen generated will oxidize the metal and cause chemical corrosion.
02. Pump performance decline
During pump cavitation, the energy exchange in the impeller is disturbed and destroyed. The external characteristic is the Q-H curve. The Q-P and Q-η curves decrease. In severe cases, the liquid flow in the pump will be interrupted and the pump will not work.
For low specific speeds, due to the narrow and long flow passage between the blades, once cavitation occurs, the air bubbles fill the entire flow passage, and the performance curve will drop suddenly.
For the medium-to-high specific speed, the flow channel is short and wide, so the bubble needs a transition process from the development to the filling of the entire flow channel. The corresponding performance curve begins to slowly decline, and then increases to a certain flow rate before a sharp decline.
Centrifugal pump is most prone to cavitation
The front cover with the largest impeller curvature, near the low pressure side of the blade inlet edge;
The low-pressure side of the volute separating tongue and guide vane near the inlet edge in the extrusion chamber
The sealing gap between the outer circle of the blade tip and the shell of the high specific speed impeller without front cover, and the low pressure side of the blade tip;
The first stage impeller in a multistage pump.
Post time: Sep-04-2020