CENTRIFUGAL PUMPSDOE-HDBK-1018/1-93PumpsMechanicalSealsIn some situations, packing material is not adequate for sealing the shaft. One commonalternative method for sealing the shaft is with mechanical seals. Mechanical sealsconsist of two basic parts, a rotating element attached to the pump shaft and a stationaryelement attached to the pump casing. Each of these elements has a highly polishedsealing surface. The polished faces of the rotating and stationary elements come intocontact with each other to form a seal that prevents leakage along the shaft. SummaryThe important information in this chapter is summarized below.Centrifugal Pumps SummaryThe impeller contains rotating vanes that impart a radial and rotary motion to theliquid.The volute collects the liquid discharged from the impeller at high velocity andgradually causes a reduction in fluid velocity by increasing the flow area, convertingthe velocity head to a static head.A diffuser increases the efficiency of a centrifugal pump by allowing a more gradualexpansion and less turbulent area for the liquid to slow as the flow area expands.Packing material provides a seal in the area where the pump shaft penetrates thepump casing.Wearing rings are replaceable rings that are attached to the impeller and/or thepump casing to allow a small running clearance between the impeller and pumpcasing without causing wear of the actual impeller or pump casing material.The lantern ring is inserted between rings of packing in the stuffing box to receiverelatively cool, clean liquid and distribute the liquid uniformly around the shaft toprovide lubrication and cooling to the packing.ME-03Rev. 0Page 10
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