Pumps & Systems - September 2007

Adaptive Hardware Metallurgy The wetted components of most slurry pumps are either manufactured from special steel or iron alloys with very high hardness or are lined with elastomers to protect them against abrasion from the slurry particles. The seal adaptive hardware must also be made from abrasion resistant metallurgy with high toughness values coupled with good corrosion resistance. Specialty metals, such as duplex stainless steel and high chrome iron, are common materials for slurry seals. Lining of wetted surfaces with elastomer coatings may be an alternative to these special metallurgies.

Figure 2. O-ring groove designs (right); wiper ring design (left).

Seal Geometry

The design of seals intended for abrasive slurry applications must include a profile that will create desirable flow patterns in the seal chamber, especially in the area of the seal faces. These profiles will avoid the creation of recirculation vortices that trap and circulate particles across critical surfaces of the seal components. A typical slurry seal profile will include line-in-line seal faces in which both the rotating and stationary seal faces share the same inner and outer seal face diameters.

Dynamic O-ring and Spring Design

If slurry particles are allowed to collect around the dynamic O-ring, the axial movement of the flexibly mounted seal face can be constrained, resulting in seal hang-up and possible failure. Slurry seal designs may include an “open” O-ring groove on the process fluid side to avoid creating cavities or crevices where particles can collect. Alternative designs may include wiper rings to isolate the O-ring groove from the process fluid.

Slurry particles can also collect around the springs, clogging the springs and adversely impacting their function. One option is to locate the springs outside of the process fluid to isolate them from the particles. Another design option is to orient the design so that the springs act on the rotating face and

Fluid Sealing Association

Sealing Sense is produced by the Fluid Sealing Association as part of our commitment to industry consensus technical education for pump users, contractors, distributors, OEMs, and reps. This month’s Sealing Sense was prepared by FSA Member Rob Phillips. As a source of technical information on sealing systems and devices, and in cooperation with the European Sealing Association, the FSA also supports development of harmonized standards in all areas of fluid sealing technology. The education is provided in the public interest to enable a balanced assessment of the most effective solutions to pump technology issues on rational Total Life Cycle Cost (LCC) principles.

The Mechanical Seal Division of the FSA is one of five with a specific product technology focus. As part of their educational mission they develop publications such as the Mechanical Seal Handbook, a primer intended to complement the more detailed manufacturer’s documents produced by the member companies. Joint FSA/ESA publications such as the Seal Forum, a series of case studies in pump performance, are another example as is the Life Cycle Cost Estimator, a web-based software tool for determination of pump seal total Life Cycle Costs. More recently, the Sealing Systems Matter initiative has been launched. It is directed to support of the case for choosing mechanical seals that optimize