204 Mechanical seal Service life and reliability of components

1、 Service life of mechanical seals

Mechanical seals rarely fail due to long-term wear, and other factors often promote the premature failure of pump mechanical seals. Therefore, the life of the seal should be considered as one Mechanical seal for kettle It is difficult to obtain accurate values due to statistical quantities. For example, mechanical seals used in some sewage pumps generally use hard ring to hard ring end face mechanical seals. If the pump shaft is in series and the shaft vibrates for a certain period of time, if hard particles enter the end face of the mechanical seal, the end face will be worn. The effective working time of the seal depends largely on the application. Pay attention to the following points to extend the service life of seals:

1. Establish a suitable working environment in the sealing chamber, such as effectively controlling the temperature; Eliminate solid abrasive particles; Control the rapid fluctuation of pressure and temperature; An effective liquid film is formed between the sealing faces (double face seal and sealing liquid are used if necessary).

2. The sealing technical specification can meet the requirements.

3. The rigidity and manufacturing precision of the pump are high.

Considering the service life of the seal, not only the one-time investment of the pump (and seal), but also the economic losses caused by seal failure, including: product losses; Investment in standby equipment; Damage to people, environment and equipment caused by fluid leakage; Labor time and spare parts required for seal replacement. The service life limit of seals can vary greatly, only a few days under chemical corrosion conditions, but 20 years in olefin applications.

2、 Reliability of mechanical seals

In addition to the above different working conditions will make a great difference in seal life, the service life of the same seal under the same service conditions will also be significantly different. This is similar to the test with rolling bearings. Therefore, when discussing seal reliability

Use statistical concepts.

We use the following two values to count the reliability of seals:

1. L10 life

The operating time when the number of failures in a part sampling array reaches 10% is called L10 service life.

2. Mean working life (MTBF)

The average working time is defined as the arithmetic mean of the interval between successive failures of the sampling,

MTBF=(L1+L2+⋯⋯+Ln)/n

Where, L1, L2 - working life of single seal.