Prevention and Mitigation of Pump Cavitation

Improve the cavitation resistance of pumps

1, reduce the necessary NPSH

(1) Water pump with double suction impeller. Since the NPSH Δhc of the double-suction pump is smaller than the NPSH Δhc of the single-stage single-suction pump, a double-suction impeller is used for the pump with the same speed n and flow Q.

(2) Properly increase the impeller inlet diameter and increase the blade inlet width. When the diameter of the impeller inlet and the inlet width of the blade increase, the absolute velocity and the relative velocity of the inlet of the impeller decrease, which indicates that the critical NPSH of the pump decreases. However, at this time, the area of ​​the leakage reduction ring at the inlet of the impeller is increased, the leakage amount is increased, and the volumetric efficiency of the pump is reduced.

(3) Add an inducer before the impeller. Induce the wheel before the centrifugal pump impeller. The inducer wheel and the pump leaf operate, and the generated pressure wheel is assembled together after being assembled coaxially. The pressure generated by the inducer pressurizes the inlet of the impeller to improve the anti-cavitation performance of the pump. However, adding an inducer will make the performance of the pump unstable. Therefore, further exploration and research are needed.

2, to improve the flow through anti-cavitation ability to reduce material member cavitation damage to the pump parts and prolong its service life, the choice often strong cavitation erosion resistance of materials. Such as cast manganese, bronze, stainless steel and alloy steel castings impeller; or coated with polymer or laser sprayed parts of the surface of the flow resistance to resist cavitation damage. In addition, finishing the surface of the flow-through component to improve its smoothness can also reduce the hazard of cavitation.

Measures to reduce pump cavitation 2. Improve cavitation erosion resistance of water inlet devices

The NPSH is closely related to the water inlet device and piping system. Therefore, a good water inlet device should be designed to increase the NPSH of the pump inlet as much as possible to meet the dynamic pressure drop requirement of the pump.

(1) Reasonably determine the water absorption height of the pump. Since the pumps are generally operated under non-design conditions, full consideration should be given to the various conditions that may be encountered in the operation of the pump. The determined water absorption height should meet the water pump performance requirements under any operating conditions.

(2) Match a reasonable inlet pipe. Minimize the length of the inlet pipe and unnecessary pipe accessories. Increase the diameter of the inlet pipe appropriately to reduce the hydraulic loss of the inlet pipe and increase the NPSH of the pump inlet. For large and medium-sized axial flow pumps, the distribution of water flow velocity and pressure in the inlet pipe is as uniform as possible, which will help prevent cavitation from occurring.

(3) A well-designed intake basin. A good pool entry not only reduces the landing of the water level in the pool, but also reduces the resistance coefficient of the inlet pipe, and the water surface in the pool does not generate a vortex. Air can be prevented from entering the pump, preventing cavitation from occurring prematurely.

3, the measures that can be taken in the operation management

(1) Try to make the pump run in the design condition accessory. According to the specific conditions of the pumping station, variable valve, variable speed, variable angle and other adjustment measures can be adopted to prevent the pump operating condition from deviating from the design condition.

(2) Control the actual speed of the pump higher than the designed speed. Since the NPSH must be proportional to the square of the rotation speed, when the rotation speed is too high, not only the NPSH margin must be significantly increased, but also the effective NPSH margin is reduced.

(3) When cavitation occurs during the operation of the water pump, the water pump inlet may be filled with a small amount of air or high-pressure water flow to reduce or avoid cavitation damage.