Cavitation phenomenon
Because the suction pump relies on atmospheric pressure to press water into the pump, so the pressure at the entrance of the pump is lower than atmospheric pressure. However, the pump inlet pressure can not be lower than the saturated steam pressure at the time of the water temperature, otherwise, the water will produce vaporization, dissolved in the water gas will also escape, the formation of steam and escape gas mixed with small bubbles. These bubbles into the impeller, with the increase in pressure, vaporization of water vapor condensation into water, the volume is dramatically reduced, forming a local vacuum, around the water to the vacuum at the impact of a great deal of force, and constantly act on the impeller, so that the impeller fatigue, and make the surface of the metal to produce shedding; at the same time, from the water escaped from the vivacious gases with the help of the water condensation of the heat released on the metal chemical corrosion effect, so that the impeller Soon appear honeycomb pockmarks, and gradually form cavities, this phenomenon is called cavitation.
Water pump cavitation occurs, will produce vibration and noise, flow, head, power and efficiency decreased significantly, and in severe cases, there will be a break in the flow. Therefore, the pump can not work in the case of cavitation. Pump head down 1%, - generally considered to have occurred in the cavitation.
Centrifugal pump vapor corrosion of the main factors affecting the pump suction height, suction pipe resistance, flow rate and pump installation location of the atmospheric pressure and working water temperature. Pump installation site of the atmospheric pressure is generally unchanged, resistance, flow rate, temperature change is not large, so the pump does not occur the main factors affecting cavitation is the suction height. Correctly determine the maximum suction height of the pump, the installation of the pump and ensure its normal and safe work is of great significance. The following describes the calculation method of water pump suction height.
Suction height
In order to make the pump does not occur vapor corrosion, the pump in the work, when the grid voltage is reduced, the pump speed down, the pump head characteristic curve correspondingly decreased. When the pump's zero head (initial head) % is lower than the actual head, the pump will not discharge water, the flow rate is zero. At this point, the motor transfer to the pump's energy will all be converted into heat, so that the pump and the pipeline in the water temperature rises rapidly, the pump strongly heat, and soon damaged. Therefore, the pump is not allowed to work for a long time at zero flow.