The function of the choma is to form a narrow and tortuous passage between the impeller and the pump shell to increase the flow resistance of the medium so as to reduce the leakage of the medium. The setting of the choma also protects the main parts of the pump from wear. After the wear of the choma, it can repair or replace the new ring and restore the normal assembly gap, which is both economical and easy to repair.
The structural form of the choma usually has radial gap type circular ring, double ring ladder type, double ring labyrinth type and axial clearance type.
The integrity of the choma and its radial clearance with the impeller should be checked first when the pump is dismantled. For example, if there are defects such as grooves in the choma or broken or gaps in excess of the specific values, the new ring should be replaced or the original ring should be repaired.
In the operation of the pump, the corresponding circumference of the choma and the impeller is simultaneously worn and the clearance increases more than the specified value, because the inner diameter of the new ring should be prepared according to the outer diameter of the impeller entrance, and the radial clearance between the impeller and the choma is 5 - 3. In the repair process, this gap is smaller, so as to improve the efficiency and prolong the service life of the pump.
Generally, the material of the ring can be gray cast iron HT200, tin bronze or tin bronze bearing alloy (babbit alloy). For the copper ring with a bearing alloy, when the gap is worn large, it is necessary to re hang the alloy, and the new ring must be replaced.
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