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Monday, 28 May 2018

MECHANICAL SEALS : INTRODUCTION | | What is a Mechanical Seal?


INTRODUCTION:
          In many industries 'Mechanical shaft seals' failures are the major cause of pump's downtime. So we decided to give some information towards mechanical seal basics.
          Mechanical sealing is a process of preventing leakage and containing fluid within the vessel (like pumps, Agitators) where the rotating part of the shaft passes through the stationary part of the pump housing or some cases, the housing rotates around the shaft.  
          Years ago, pump shafts are sealed by using gland packing rope. Gland packing is braided material, rope like material. This type of seal required a skilled worker and a small amount of leakage just to lubricate the packing and keep it cool. without this arrangement the packing gland becomes hard. While the shaft rotates friction produces between rope and shaft this causes wear of packing. Packing need to contact the shaft it will wear the shaft too. 
          After facing these kind of problems "Mechanical Seal" development came, which fulfills the task of controlling the leakage produced around the pump shaft with two very flat surfaces (one rotating and one stationary or constant). These mechanical seal faces also require some (very small) leaks across the faces, to form a hydrodynamic film, this leakage is usually evaporating and not identifiable. This fluid comes from processed fluid or from an external source. To achieve a precise gap for this fluid film is a design challenge.
          Now a days most of the pump shafts are sealed by using mechanical seals. However, due to the sensitive parts used in this new sealing system, mechanical seal failure are the biggest cause of pump down time.


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