A cool seal is a good Seal!

A cool seal is a good Seal!

A cool seal is a good Seal!

Mechanical Seals are considered to be complicated and most important part of pump and it is often blamed for the equipment failure while Pump operations, Liquid Conditions and Mechanical condition of Pump are most probable reasons for it.

Mechanical Seal faces are the most vulnerable parts of any mechanical seal, but other parts such as the secondary sealing elements like O-rings, bellows, polymer wedges or metal parts such as springs, drive pins, or set screws also may affect the life of the seal. It has been observed that metal parts cause least chance of seal failure and last very long. Rubber and polymer parts need to be replaced when open seal due to whatsoever reason as these parts deformed once install and use for sometime. Premature failure of these components occur due to improper fitting and un-suitable liquid conditions.

Mechanical Seal failures may be categorized on the basis of MTBF [Mean time between Failures] as either Infant, Mid life or Wear-out.

Infant failures are most often caused by incorrect seal selection, installation or startup. Such failure happens either immediately or after few hours of operation. Incorrect selection causes damage to seal due to liquid conditions which proves severe to its parts. In improper installation seals faces damaged due to excessive tension or cause leakage due to insufficient pressurization of faces.

Mid life failures occur unexpectedly after a considerable run period. Mid-life failures are quite difficult to predict because they usually are the consequence of a process operation or equipment induced transient, which could not be tolerated by the face materials. Transient operating conditions may be as a result of a malfunction of a component in the pump or an unintended process deviation. Most common causes are bearing failure, disturbance in alignment, wearing of parts of rotary assembly of pumps or other equipments, dry running ,cavitation, contamination in liquid, change in characteristics of liquid etc.

Wear-out failures are occurred due to ending of any of the faces. Seals faces worn out fully to its neck and other rubber and polymer parts fully distorted. It is ultimate and most satisfactory for Manufacturer and user if happens naturally. However time of worn out of faces and other parts depends on the various factors.

Common distress symptoms of seal face failure are pitting, blistering, chipping, grooving, heat and thermal shock cracks. These symptoms can be diagnosed by skilled and qualified Engineer and taken care for best possible life of seal.

Life of a seal depends to a large extent on its ability to maintain a thin fluid film in between the mating faces and duration and extent of mechanical contact between the rubbing areas of these faces. Too much contact may overheat the materials; not enough contact may cause high leakage rates.

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