What is cavitation
When the local pressure of the liquid in the pump drops to a critical pressure, bubbles are created in the liquid. Vaporisation is the whole process of bubbles gathering, moving, splitting and eliminating. The critical pressure is generally close to the vaporisation pressure.
Hazards of pump cavitation
1、Corrosion of overflow components
There are two causes of corrosion.
One is due to the high frequency (600~25000HZ) impact generated when the bubble breaks, with a pressure of up to 49Mpa, resulting in mechanical stripping of the metal surface.
Secondly, due to the heat released during vaporisation and the temperature difference cell effect to produce hydrolysis, the oxygen produced oxidises the metal and chemical corrosion occurs.
2、Drop in pump performance
When the pump cavitation impeller energy exchange is disturbed and destroyed, the external characteristics of the performance is Q-H curve, Q-P, Q-curve decline, serious will make the pump in the liquid flow interrupted, can not work.
For low specific speeds, the performance curve drops abruptly due to the narrow and long flow paths between the blades, and once cavitation occurs, bubbles fill the entire flow path.
For medium to high ratios, the flow path is short and wide, so that a transition is required from the development of bubbles to filling the entire flow path, and the corresponding performance curve starts slowly and then increases to a certain flow rate before dropping sharply.
Measures to avoid cavitation in lobe pumps
1. In the design, the rate of change of each section of the circulation section should be made small, while the wall through which it passes should strive to be smooth.
2, in a certain suction height, the lobe pump's revolution number increase should be a certain limit, because the larger the revolution number, the larger the flow, the smaller the suction height. Therefore, increase the lobe pump's revolution number will inevitably reduce its suction height. Therefore, in a certain suction height, increase the number of revolutions is a certain limit, otherwise it will occur cavitation and lead to the normal operation of the pump damage.
3. It is advisable to keep the lobe pump constantly operating near its design working conditions.
4. minimise resistance in the inlet pipe, which should therefore be both straight and short, and correctly determine the suction height of the lobe pump.
5. Use appropriate materials for components in areas prone to cavitation.