Mechanical seals are designed to produce an acceptably low level of leakage to function effectively. They are controlled leakage devises, not zero-leakage devices.
Here is the reason that seal faces cannot be permitted to run dry: the frictional heat buildup of hard contact will very quickly cause them severe damage and lead to extensive leakage. Thus, seal faces are designed to allow a very thin film of liquid to exist between and migrate across them.
Many individual internal and external factors, as well as interactions between them, will affect the rate of seal leakage. The factors include:
- Sealing pressure
- Face loading
- Sealing face materials
- Ambient temperature
- Fluid viscosity
- Vapor pressure
- Normal tolerance variations
- Characteristics of the liquid to be sealed
Generally speaking, a leakage rate of 10 drops per hour or less per seal is considered an acceptable leak rate for mechanical seals in pump applications.
However, many pumps operate well below these limits.
Having visibility into a seal’s regular (and irregular) leakage history is now possible. As plant management grows more complex, a decision to integrate automated central condition monitoring into thermal fluid operations especially can make it possible to strike dangerous seal leaks from the list of operating headaches and preventable problems.
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