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Tuesday, August 4, 2009

Classification of Seals By Arrangement

Sealing arrangement can be classified into two groups:

1. Singgle seal installations

  • Internally mounted
  • Externally mounted

2. Multiple seal installations

  • Double seals
  • Tandem seals

Single seals are used in most applications. This is the simples seal arrangement with the least number of parts. An installation can be reffered to as inside mounted or outside mounted, depending on wether the seal is mounted inside or outside the seal chamber. The most common installation is an inside mounted seal. Here the liquid under pressure acts with the spring lead to keep the seal faces in contact.

Outside seals are considered to be used for low pressure applications since both seal faces, the primary ring and mating ring, are put in tension. This limit the pressure capability of the seal. An external seal installation is used to minimize corrosion that might occur if the metal parts of the seal were directly exposed to the liquid being sealed.

Multiple seals are used in applications requiring:

  • A neutral liquid for lubrication
  • Improved corrosion resistance
  • A buffered area for plant safety

Double seal consist of two single seal back to back, with the primary rings facing in opposite dirrection in the real chamber. The neutral liquid, at a pressure higher than that of the liquid being pumped, lubricates the seal faces. The inboard seal keeps the liquid being pumped from entering the seal chamber. Both inboard and outboard seals prevent the loss of neutral lubricating liquid.

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