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Before packing material is the main seal for centrifugal pump in China, but in oilfield it is inconvenient to replace the packing seal time by time, it is too easy to damage, compare with packing, mechanical seal is much more durable, even if with high cost. 
Centrifugal pump mechanical seals consist of two basic parts, a rotating element attached to the pump shaft and a stationary element attached to the pump casing. Each of these elements has a highly polished sealing surface. The polished faces of the rotating and stationary elements come into contact with each other to form a seal that prevents leakage along the shaft.