Jiaxing Burgmann Import & Export Co., Ltd.

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INSTRUY NEWS

Factors Affect the Mechanical Seal Performance I

  • Date:2016-10-12
  • Abst:

    Absolutely, mechanical seal design can influence film thickness by balancing the closing forces on the sealing interface in such a way that the sealing interface does not become overloaded as process pressures increase. A closing force that is too high will lead to a fluid film at the sealing interface that is too thin, generating detrimental heat.

    Another way to influence film thickness is to design surface features at the sealing interface that promote hydrodynamic lift between the rotary and stationary sealing elements. This can help create a purposeful separation at the sealing interface that results in a thicker fluid film that provides cooling and decreases face wear.

    Primary seal material selection can influence seal life as well. Chemical or process compatibility is just one consideration. Harder materials are more resistant to abrasive processes, but if both sealing elements are hard materials, the wear characteristics may be less desirable in a nonabrasive application.

    Using one sealing element made of a softer material and one that contains lubricating components, such as graphite, decreases friction for starting and incidental contact. The use of composite hard faces will also reduce friction by providing microscopic reservoirs of system fluid at the interface.

    Thermal conductivity of materials will dissipate heat away from the sealing interface, promoting mechanical seal life. Material toughness also can play a dominant role in mechanical seal life. The inherent material surface texture may also play a role in promoting desirable film thickness.

    Note that many mechanical seal failures are result from failed secondary seals that have exceeded chemical compatibility, pressure or temperature limits. Metal parts must be compatible to avoid corrosion, and springs and other hardware must hold up in service.

    Additionally, process and seal environmental controls greatly contribute to a cool, clean lubricating film at the sealing interface. If the process fluid is a slurry mixture, process pressure will drive the particulate-laden fluid into the sealing interface, resulting in abrasion and accelerated wear.

    Environmental controls, such as a restriction bushing and clean flush, can isolate the mechanical seal from the harsh process so the seal is mostly sealing the cleaner, cooler flush fluid. In other cases, the pump product may crystallize and abrade the sealing interface and causing premature wear. However, product crystallization can be prevented by using temperature controls, quenching the atmospheric side of the sealing interface, or using a double seal with a buffer or barrier fluid.