Types of Mechanical Seals for the Centrifugal Pumps and Selection of the Mechanical Seal

There are various types and arrangement of the mechanical seals being used for the centrifugal pumps. Some of the commonly used ones are described below:

The pusher type of mechanical seals move axially along the rotating shaft or the sleeve to maintain the contact with the faces of the seal. This feature of these seals helps compensate for the wearing that may occur at the seal face, and wobbling due to misalignment. The pusher types of mechanical seals are used commonly, are less expensive and are easily available in the market in wide range of sizes and designs. The only disadvantage of these seals is that they tend to hang up and sometimes there is fretting of the shaft.

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The unbalanced types of mechanical seals are used under drastic conditions where there are vibrations, misalignment of the shaft, and the problem of the cavitation of the fluid. These mechanical seals are inexpensive, allow lesser leakage of the fluid and are highly stable. However, these seals can operate only under low pressure range and if the force of the fluid exceeds certain limits the lubricating film between the faces squeezes out and the seal fails.

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These are relatively simple mechanical seals that have to be properly set and aligned on the shaft or the sleeve of the pump.

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As the name suggests, the non-pusher or bellow type of mechanical seals don’t have to be moved axially to maintain their contact with the faces. These seals can work under low temperature and high pressure applications. The bellows used in these seals should be upgraded so that they can work under the corrosive environments.

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The balanced mechanical seals have the ability to sustain higher pressures across the faces and they generate lesser heat thus they are suitable for handling liquids that have low lubricating capacity and hydrocarbons that have high vapor pressure.

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The major advantage of the cartridge seals is that they don’t require complicated setting during the installation as required by the conventional seal. This helps reducing errors associated with seal setting and eventually also reduces the maintenance required.

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