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In the single acting water ring vacuum pump parts damage, the shaft damage occupies a large proportion. Damage to the pump shaft includes bending, cracking and breaking.

The bending of the pump shaft is mostly due to the insufficient stiffness of the sleeve and the large imbalance of the impeller. The bending direction and size of the shaft can be measured by the following methods:

Place the shaft horizontally on the support, adjust the two support points (either the center hole of pump shaft or the shaft neck) to the same height, select several equidistant sections on the shaft, and measure the radial runout in four directions (i.e. once a week when rotating 90 ° with a dial indicator) and make records. According to this data, the bending values in four directions can be obtained, and the maximum bending direction and size can be found by graphic method, so that straightening can be carried out.

The crack and fracture parts of pump shaft often occur in the place of local stress concentration, such as the edge of keyway, sudden change of diameter and so on. The cause of the damage is often caused by the vibration.

If the pump shaft appears fatigue crack (the precursor of breaking soon), it should be replaced in time. If it can not be replaced due to objective factors and needs to continue to use, the temporary remedy is to repair the cracks. When using the pump shaft after repair welding, it is necessary to pay attention to the change of repair welding area to avoid accidents.

In the use of single acting water ring vacuum pump, the common failure is the fracture of pump shaft (especially for the pump with large air volume). The fracture surface is generally perpendicular to the axis line, very neat, like knife cutting, the whole section is mostly smooth and metallic luster, a small part is rough. Obviously, this is the fracture characteristics caused by fatigue failure.

The main cause of fatigue damage is that the pump shaft in the process of operation, the pump cavity gas on the pump shaft caused by the force, which is also known as radial force.

In addition to the radial force in the water ring vacuum pump, the unreasonable structure is also an important reason that can not be ignored. It mainly includes:

At present, the shaft and impeller of water ring vacuum pump are all in one-stage dynamic fit, and there is no 0-type sealing ring at the keyway. The liquid in the pump (especially when the corrosive liquid is used as liquid ring in chemical industry) will enter the shaft hole through the fit clearance and keyway, which will corrode the shaft hole of the shaft and impeller, and greatly reduce the fatigue strength. The increase of fit clearance after corrosion and wear (some of which are ground into elliptical shaft holes) not only affect the performance, but also aggravate the vibration and promote fatigue fracture.

The general water ring vacuum pump shaft has not been heat treated, so the fatigue strength is low. In order to prevent fracture, the pump shaft should at least be quenched and tempered, and nitriding treatment should be carried out where conditions permit.

In the design, it is necessary to avoid large section mutation. Fillet connections are applied instead of sharp corners at the transition. The surface finish should not be low, especially in the place where the shaft is easy to break. During the processing, the circumferential machining of the transition parts of different shaft diameters should ensure the quality, and the size and smoothness required by the drawings should be strictly followed. There should be no knife marks, scratches, bumps and other defects on the surface and transition of the pump shaft.

The fatigue damage of pump shaft is very harmful to production, which is a problem of great concern to users. The solution is: according to the size of radial force to check the fatigue strength of the pump shaft, when using corrosive gas and liquid ring, the corresponding corrosion-resistant materials should be used, the pump shaft must be quenched and tempered, and the quality must be guaranteed during processing.