Gene Vogel
EASA Pump & Vibration Specialist

"Pump Seals—Advanced" by Gene Vogel, presented at the EASA Convention 2011, provides a comprehensive overview of mechanical seals used in pumps. It categorizes seals into four main types: pusher vs. non-pusher, component vs. cartridge, balanced vs. unbalanced, and single vs. double (or triple) seals. Each type has distinct characteristics and applications. The document also discusses various seal face materials, including carbon on ceramic, silicon carbide, tungsten carbide, stainless steel, and Ni-resist iron, highlighting their advantages and limitations. Heat transfer and tensioning are crucial for seal performance, with excessive heat being a common cause of seal failure. Proper cooling flow and tensioning are essential to maintain seal integrity. Secondary seals, such as O-rings and gaskets, are used to prevent liquid bypass and their material selection depends on the fluid being pumped and operating temperature. Seal flush plans and cyclonic separators are discussed as methods to improve seal reliability by removing heat and abrasive contamination. The document also emphasizes the importance of proper design, material selection, and operational practices to ensure the reliability and performance of mechanical seals in pumps.

Key Points and Takeaways

• Seal Categories:

  • Pusher vs. Non-Pusher Seals: Pusher seals use a spring to apply pressure, while non-pusher seals use a bellows or diaphragm.
  • Component vs. Cartridge Seals: Component seals require assembly, while cartridge seals are pre-assembled units.
  • Balanced vs. Unbalanced Seals: Balanced seals balance hydraulic pressure, while unbalanced seals rely on mechanical compression.
  • Single vs. Double (or Triple) Seals: Single seals have one barrier, while double seals use two pairs of seal faces with a barrier fluid.
     

• Seal Face Materials:

  • Carbon on Ceramic: Inexpensive, cool operation, poor abrasive resistance.
  • Silicon Carbide: Hard, chemically inert, good for abrasive applications, can fracture under thermal stress.
  • Tungsten Carbide: Very hard and strong, resistant to thermal stress, can corrode with strong chemicals.
  • Stainless Steel: Inexpensive, good mechanical strength, prone to corrosion and galling.
  • Ni-Resist Iron: Inexpensive, moderate corrosion resistance, relatively soft.
     

• Seal Dynamics:

  • Heat Transfer: Excessive heat is a common cause of seal failure; proper cooling flow is necessary.
  • Tensioning: Combination of mechanical and hydraulic tension is essential for effective sealing.
     

• Secondary Seals:

  • O-rings and Gaskets: Material selection depends on the fluid being pumped and operating temperature.
     

• Seal Flush Plans:

  • Flush Lines: Circulate liquid to carry away heat; proper metering is necessary to prevent efficiency loss.
     

• Cyclonic Separators:

  • Abrasive Contamination: Cyclonic separators remove abrasive contamination from the flush line.

This summary and the key points provide a clear understanding of the various aspects of mechanical seals in pumps, emphasizing the importance of proper design, material selection, and operational practices.