The cavitation and the damage of pump

The cavitation and the damage of pump

1.The cause of cavitation

The direct cause of cavitation of the pump is that the local pressure in the pump is lower than the saturated vapor pressure of water. There are several reasons for the low pressure in the pump:

(1) The pump is installed too low. As the pump mounting height increases, the vacuum degree of the pump inlet increases, causing the pressure drop in the pump to be too low.

(2) The actual working condition of the pump deviates from the design point.When the water pump is running under non-design conditions, it may also produce a bottom-up zonal vortex under the impeller (called vortex band).When the pressure of the vortex belt center drops to the saturated vapor pressure, the vortex belt becomes the cavitation zone.When the vortex belt is inserted into the pump, it can not only promote and aggravate the cavitation of certain parts of the pump, but also cause the strong vibration of the unit and make a roar.

(3) The water inlet of the pump is not good.The inlet velocity distribution of the impeller inlet is not uniform due to the uneven distribution of the pressure distribution of the elbow water inlet flow.The flow of water into the tank causes the water to be prewhirled or the air to be brought into the water pump, which also causes the flow velocity and pressure distribution of the impeller inlet to be uneven, which leads to the occurrence of cavitation and cavitation.According to the foreign cavitation test data, the gas in the water is larger, and the cavitation starts earlier.

(4) The elevation of the pump installation site is higher, and the water temperature of the pump is higher.At high altitude, atmospheric pressure is low, so the pressure of pump suction inlet is lower;And the higher the water temperature, the greater the pressure of saturated vapor, the easier the water will vaporize.

2. The damage of water pump cavitation

The cavitation of water pump is a kind of complicated physics, chemical phenomenon, the occurrence and development of cavitation, can cause the following damage to the pump.

(1) Water pump performance deterioration

In the process of produce cavitation, because the water contains a lot of bubble, destroy the rule of the normal flow of the water, changing the flow area and flow direction of the flow passage, and energy exchange between the impeller and the flow stability is destroyed, energy loss increased.

(2) The flow component is damaged by the denudation

When the bubble is after the water flow to high, due to the increased water pressure of bubble around, make bubble burst quickly, the water flow around the bubble particle high ground to the center of bubble shock, water particle smashed into each other, have strong water hammer.

(3) Generate noise and vibration

In the process of continuous formation and collapse of the bubble, a strong pulse pressure can be generated in the pump due to the impact of the particles in the flow and the impact of the surface of the overflow parts.As a result, the pump produces a high frequency of noise and vibration when cavitation occurs.Vibration can damage the parts and seats of the unit.In particular, the frequency of cavitation vibration is close to the frequency of vibration of the unit, which can lead to resonance phenomenon and even serious consequences.