Elements of a Successful Sealing Program

Written by Christopher Little, A.W. Chesterton Company

Page 2 of 2

Design Causes

The sealing system itself can account for approximately 28 percent of total seal failures. The overall system consists of the actual shaft sealing method, materials and the ancillary equipment or support systems required to extend seal life cycles. Unfortunately, at the local level, sufficient knowledge of these components is not always available to the end user. However, reputable seal companies can offer the requisite service factor and seal knowledge.

Sealing systems specification is based on a few basic principles: inherent knowledge of basic seal design, complete understanding of the pros and cons, the right selection of seal materials for the application and what support systems work best with what sealing methods and in what applications.

Design considerations include:

Proper selection and application of the sealing method
- Mechanical seals
  - Seal Configuration
    - Single or double liquid lubricated
    - Gas lubricated
    - Split seals
    - Rotary or stationary design
    - Inside or outside design
    - Pusher or bellows design
  - Materials
    - Face materials
    - Secondary seals (o-rings or graphite)
    - 316 stainless steel or high alloy metals
- Mechanical packing
  - Packing Configuration
    - Inter-braid, square braid or braid over core
    - Rotary or reciprocating technology
    - Live-load systems
    - Solids removal technology
    - Combination sets
  - Materials
    - Yarn type
    - Lubrication technology
    - Blocking agents
    - Corrosion inhibitors
- Support Systems
  - Barrier/Buffer Tanks
  - Environmental controllers
  - Clean Flush
  - Quench & Drain
  - Cooling plans

All the components above are the same system attributes discussed when determining life cycle analysis for a particular sealing system (less the pump and other associated capital equipment).

Conclusion

Considering these three factors needs to be a team effort between multiple functional areas within the plant: maintenance crafts, operations and procurement/vendor activities. Operation's main concern is to deliver a quality end product to the customer while minimizing equipment failures through proper monitoring and operation of equipment. Maintenance crafts must provide quality, timely repairs while ensuring equipment availability to operations. Procurement works with vendors to deliver properly specified equipment and materials and minimize mechanical failures associated with specifying improper materials or equipment design attributes.

Ideally, the final outcome is a maintenance group that embraces a best practices approach because they are confident that operations is looking out for their best interest-the equipment. The maintenance and operations groups together feel confident that their equipment vendors, working with procurement, are providing the correct product specifications to meet the final goal-reliability improvements. If properly managed, a cross-functional seal team considering these three factors will no doubt have a positive impact on plant mean time between failures.

Christopher Little is the global product line manager, mechanical seals for A.W. Chesterton Company, 860 Salem Street, Groveland, MA 01834, 978-469-6554, Fax: 781-481-7411, www.chesterton.com.