Mechanical seals - Assembly, maintenance and failures

The ever-changing technical and economic requirements of the industrial world are leading to increasingly widespread use of dynamic seals.

The main aim of this article is to provide both users and manufacturers with practical recommendations for ensuring the reliability of a mechanical seal. The stakes are high, both in economic terms, due to the costs generated by failures, and in terms of the safety of people exposed to the risks induced by these failures.

Existing statistics from manufacturers and users in France and abroad show that, in general, the reliability of a mechanical seal can be called into question by :

• inadequate selection: incomplete specifications, materials, assembly configuration, etc. ;

• mechanical problems: unsuitable storage, assembly errors, shaft misalignment, bearing failure, etc. ;

• process problems: cavitation, de-priming, operation of machines outside their normal operating range, changes in the characteristics of the fluid conveyed;

• operating system failures: commissioning, interruption of fluid circulation, insufficient pressure in the mechanical seal, etc. ;

In most cases, the mechanical seal is the first to fail, but not necessarily the cause of the damage.

Mechanical seal failures and leaks involving hazardous, toxic, flammable or corrosive products can have very serious consequences for the environment, both for personnel and equipment: fire, explosion, pollution, poisoning, etc. Both manufacturers and users are well aware of this risk. Both manufacturers and users are well aware of this risk. As a result, manufacturers are striving to design fittings that offer the best possible reliability, taking into account operating conditions and the nature of the products conveyed. However, whatever the reason, the risk of leakage remains. The safety level of sealing devices must therefore be adapted to this risk.

Mechanical seal expertise provides information for maintenance, or identifies the cause of seal failure. By taking action on operating conditions, materials, technology and assembly faults, it is possible to optimize the service life and reliability of mechanical seals. It should therefore be carried out systematically whenever a mechanical seal is dismantled, whether as a result of damage or not, with a view to possible repair.

The manufacturer therefore relies on his knowledge of the technology, his experience and, most importantly, the quality and reliability of the information he receives to select the equipment best suited to the user's needs. So it's important that the...