Understanding PTFE Packing in Axial Split Case Pumps
Proper sealing is critical to ensuring the reliability and performance of an axial split case pump. Among the many sealing options, PTFE (Polytetrafluoroethylene) packing is a widely adopted solution thanks to its unique chemical and physical properties. This guide explores the advantages and limitations of using PTFE-based packing in axial split case pumps, helping you make informed decisions for your sealing applications.
Key Properties of PTFE Packing
PTFE possesses several properties that make it ideal for use in pump packing materials:
1. Excellent chemical resistance. PTFE is inert to a wide range of corrosive fluids, including strong acids, bases, solvents, and powerful oxidizers like nitric acid and chlorine dioxide.
2. Low coefficient of friction. Its smooth, non-wetting surface minimizes wear and reduces energy consumption at the packing-shaft interface.
Limitations of PTFE in Axial Split Case Pump Applications
Despite its benefits, PTFE exhibits certain limitations when used in pump packing:
1. Cold deformation (creep). Over time and under pressure, PTFE packing can densify and extrude from the stuffing box, requiring frequent adjustments.
2. Low thermal conductivity. Pure PTFE retains heat and may overheat when exposed to the friction of a fast-rotating shaft, necessitating higher leakage rates to prevent damage.
3. High thermal expansion. PTFE expands significantly with temperature, increasing contact pressure on the pump shaft and bore.
Types of PTFE-Based Packing Used in Axial Split Case Pumps
PTFE Fiber Packing
PTFE fiber packing is available in dry form or coated with PTFE dispersions and lubricants. This type is best used in applications involving aggressive chemicals or food-grade requirements. It requires careful monitoring of operational limits and frequent adjustment during service.
Expanded PTFE (ePTFE) Packing
ePTFE packing, often impregnated with graphite, offers better thermal conductivity and reduced heat sensitivity compared to traditional PTFE fiber packing. It is a suitable option for higher-speed applications but may still deform under high pressure.
PTFE-Coated Packing
When full chemical resistance isn’t required, PTFE coatings can be applied to other fibers to combine the benefits of PTFE with the strength of base materials. Common combinations include synthetic fibers, glass, aramid, and graphite.
• Synthetic/glass fiber with PTFE: Offers better resilience, reduced extrusion, and less sensitivity to adjustment.
• Aramid with PTFE: Ideal for high-wear conditions.
• Carbon/graphite with PTFE: Suitable for high-speed, high-temperature, and mildly corrosive services.
Conclusion
PTFE packing offers excellent chemical resistance and low friction, making it a valuable sealing solution for axial split case pumps. However, understanding its thermal and mechanical limitations is essential. By selecting the appropriate type of PTFE-based packing and adhering to manufacturer guidelines, operators can maximize sealing efficiency, equipment longevity, and overall pump reliability.
