Method to improve cavitation resistance of stainless steel high temperature and corrosion resistant pump
The stainless steel high temperature and corrosion resistant pump will cause cavitation in the long-term operation process. Many bubbles in the impeller path will damage the continuity of the fluid medium. The power and flow of the pump will be greatly reduced, and the stainless steel multi-level The pump will produce intense noise and sensation, causing corrosion of the parts. Therefore, it is very necessary to improve the anti-cavitation function of the stainless steel high temperature and corrosion resistant pump.
Ways to improve the cavitation resistance of stainless steel high temperature and corrosion resistant 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 that of the single-stage single-suction pump, a double-suction impeller should be used for pumps with the same speed n and flow Q.
(2) Appropriately increase the diameter of the impeller inlet and increase the width of the blade inlet. When the impeller inlet diameter and blade inlet width increase, the absolute velocity and relative velocity of the impeller inlet decrease, which shows that the critical cavitation margin of the pump decreases. But at this time, the area of the leakage reduction ring at the inlet of the impeller increases, the leakage increases, and the volumetric efficiency of the pump will decrease.
(3) An inducer is added before the impeller. Set the inducer before the centrifugal pump impeller. The inducer and the pump's blades operate, and the pressure wheel produced by it runs coaxially after assembly. The pressure generated by the inducer pressurizes the inlet of the impeller to improve the cavitation resistance of the pump. However, the addition of an inducer will make the performance of the pump unstable, so further exploration and research are needed.
2. Improve the anti-cavitation ability of the flow parts materials In order to reduce the damage of cavitation to the flow parts of the water pump and prolong its service life, materials with strong anti-cavitation properties are often selected. Such as casting manganese, bronze, stainless steel, alloy steel and other materials to cast the impeller; or use polymer coating or laser spraying the surface of the flow parts to resist cavitation damage. In addition, finishing the surface of the over-current parts can improve its smoothness and reduce the harm of cavitation.
2. Improve the anti-cavitation ability of the water inlet device
The cavitation margin is closely related to the water inlet device and piping system. Therefore, a good water inlet device should be designed to increase the cavitation margin of the pump inlet as much as possible to meet the requirements of the dynamic pressure drop in the pump.
(1) Reasonably determine the suction height of the pump. Since water pumps generally operate under non-design working conditions, various working conditions that may be encountered during pump work should be fully considered, and the determined water absorption height should meet the requirements of pump water absorption performance under any working conditions.
(2) Choose a reasonable inlet pipe. Minimize the length of the water inlet pipe and unnecessary pipeline accessories, and appropriately increase the diameter of the water inlet pipe to reduce the hydraulic loss of the water inlet pipe and increase the cavitation margin of the pump inlet. For large and medium-sized axial flow pumps, the water flow velocity and pressure in the inlet pipe are distributed as evenly as possible, which will help prevent the occurrence of cavitation.
(3) Well-designed inlet tank. A good inlet pool can not only reduce the drop of the water level in the pool and reduce the resistance coefficient of the inlet pipe, but also the water surface in the pool is stable and does not produce vortex. It can prevent air from entering the pump and prevent cavitation from occurring prematurely.
3. Measures that can be taken in operation management
(1) Try to make the water pump run in the design condition. According to the specific conditions of the pump station, adjustment measures such as variable valve, variable speed, and variable angle can be adopted to prevent the pump operating conditions from deviating too far from the design conditions.
(2) Control the range of the actual speed of the water pump higher than the design speed. Since the cavitation margin must be proportional to the square of the speed, when the speed is too high, not only the necessary cavitation margin is greatly increased, but also the effective cavitation margin is reduced.
(3) When cavitation occurs during the operation of the pump, a small amount of air or high-pressure water can be filled into the water inlet of the pump to reduce or avoid the damage of cavitation.
