Centrifugal pumps are corrosion-resistant centrifugal pumps commonly used in industrial production. Fluoroplastic centrifugal pumps are suitable for transporting corrosive solvents such as acid, alkali and salt. The operating temperature can reach 150 degrees. Cavitation of centrifugal pumps is often heard. What is the reason for that? How many meters are the installation height and suction height of the centrifugal pump? The cavitation phenomenon of the centrifugal pump means that the saturated vapor pressure of the liquid being conveyed is equal to or lower than the pressure at the pump inlet (actually at the blade inlet) due to the saturated vapor pressure at the conveying temperature. Partial vaporization will cause noise and vibration of the pump. In severe cases, the flow rate, pressure head and efficiency of the pump will drop significantly. Obviously, the phenomenon of cavitation is not allowed in the normal operation of the centrifugal pump.
The key to avoiding cavitation is to install the pump at the correct height, especially when transporting volatile liquids with high temperatures. When the cavitation phenomenon occurs, the pump will generate noise and vibration, which will drastically reduce the performance of the pump's lift, flow rate and efficiency. At the same time, it will accelerate the damage of materials and shorten the service life of the parts. Therefore, the suction height of the pump must be limited. Prevent the liquid from vaporizing in large quantities to avoid cavitation. The height between the center of the suction port of the centrifugal pump and the liquid level of the liquid storage tank is called the suction height. Assuming that the inlet of the impeller is vacuum, the resistance of the suction pipeline is zero, and the liquid level is a standard atmospheric pressure, then the theoretical geometric height is 10.33 meters, however, due to various resistance losses in the suction pipe of the pump, and the unfavorable factors such as the impossibility of complete vacuum at the inlet of the pump impeller, plus the necessary NPSH at the inlet of the pump, the suction height of the general centrifugal pump is not high. More than 4-5 meters.
The cavitation phenomenon of centrifugal pump To prevent the pump from cavitation, it is necessary to make the liquid per unit weight at the inlet of the pump impeller exceed the excess energy of the vaporization pressure. When the suction height of the centrifugal pump is too large and the liquid temperature is relatively high, the suction pressure is less than or equal to the saturated vapor pressure of the liquid, then the liquid will boil and vaporize at the pump inlet in this environment, forming a space full of steam in the pump shell. As the pump rotates, the air bubbles enter the high pressure area. At the moment of condensation, the particles collide with each other, resulting in a high local pressure. If these bubbles rupture and condense near the metal surface, the liquid particles are like countless small warheads, hitting the metal surface continuously, causing cracks on the metal surface, and even local peeling, making the impeller surface honeycomb, while the bubbles are in the shape of a honeycomb. Some active gases such as oxygen enter into the cracks on the metal surface, and the metal is subjected to chemical corrosion by the heat released when the bubbles condense. The above phenomenon is cavitation.
