What is a Hermetic Bellows?

An Air-Tight Assembly critical for many industries

Hermetic1 Hermetic seals maintain a positive, impermeable boundary between process systems and unwanted exposure or contamination while still allowing for flexibility, expansion, and contraction in a controlled manner. These air-tight assemblies are ideal for cleanrooms, EPA clean-air regulations compliance, or when personnel safety is necessary. Hermetic bellows are available in many sizes, different metallurgies for various applications, and are capable of a high range of travel for applications requiring a long stroke. Hermetic bellows effectively seal systems in high-stakes applications where a small leak could endanger personnel, risk companies’ capital, reputations, and future business. When quality and reliability matter, use only the best quality custom designed edge-welded hermetic bellows for every application.

Defining features of Hermetic Bellows

Hermetic bellows are inherently different and offer numerous advantages over traditional mechanical seals. Those advantages include:
  • No elastomers to wear or replace; hermetic bellows are relatively maintenance-free and leak-free for many life cycles.
  • Hermetic bellows are all-metal, corrosion-resistant materials optimized for each application to keep wetted surfaces in like-new condition at all times.
  • Precise linear motion to eliminate column instability or “bellows squirm.”
  • Flexaseal’s bellows are leak-tight to a minimum of 1 x 10-9 cubic centimeters per second (scc/sec.)
  • Compact nesting capabilities are inherent to edge-welded hermetic bellows, providing a long cycle life and a wide range of travel.

Typical applications for Hermetic Bellows

Hermetic bellows serve countless applications across many industries. Hermetic bellows offer a reliable and efficient solution whenever a system demands a positive, leak-tight seal in a dynamic environment.
  • Filter Dryers – A gas-tight seal is used with CFC and HCFC refrigerant dryers to achieve zero leakage systems.
  • Freeze Dryers – Bellows seals are used in vacuum environments to maintain high purity standards.
  • Compressors – Bellows seals eliminate leakage past traditional dynamic seals. Bellows seals on compressor valve stems hermetically seal the valve while still allowing for axial movement, maintaining a zero-leakage compressor.
  • Volume Compensators – Hermetic bellows devices prevent cavitation by maintaining positive pressure during volume fluctuations.
  • Hydraulic or Pneumatic Actuators – Hermetic bellows can act as a piston to convert fluid pressure into linear motion, particularly in high-pressure applications where a dynamic seal could fail or critical systems where any leakage is unacceptable.
  • Vibration Dampers – Hermetic bellows are highly effective at isolating vibration.
  • Semiconductor and Aerospace Manufacturing – Industries that use ultra-high systems may incorporate manipulators or linear translators, corrosive chemical washes, high-energy plasma etching, wafer production, and intense electromagnetic radiation in their manufacturing processes. Sealed areas and clean rooms can use hermetic equipment to eliminate personal and environmental exposure.
  • Hazardous Materials – Hermetic bellows devices provide a positive boundary when handling radioactive material, toxic emissions, and carcinogenic by-products.
  • Energy Generation – Hermetic bellows provide a leak-free boundary between process systems in heat exchangers like boilers or condensers and are used as sealing solutions for extreme pressures and temperatures, such as cryogenic applications.
  • Pharmaceutical Processing – Hermetic bellows devices are ideal for containing biohazardous material and eliminating micro contamination.

Choosing the best Hermetic Bellows for your project

Specialty edge-welded hermetic bellows seals are ideal for many of the uses described above. Engineers can design customized hermetic bellows to optimize performance for each application. System chemistry requirements may specify different metallurgy, and only top-quality metal alloys should be selected. Hastelloy™, Inconel®, titanium, Monel®, and 347 SS metals are available for use depending on the project. The best bellows manufacturers feature flexible diaphragms, plates in varying thicknesses, full spring rate testing, and a diverse range of fixtures and end fittings. Fabrication teams and engineers should work together to ensure strict quality control in every process, from stamping sheets of foil stock to pressure-testing the completed assembly. TIG welding (Tungsten Inert Gas) every joint creates efficient, clean, and long-lasting welds. These edge-welded bellows are vastly superior to less precise formed bellows in their quality and longevity, reducing life-cycle maintenance costs and down-time. Once welded, hermetic bellows should be leak tested with helium tracer gas using a mass spectrometer to ensure every seal is completely leak-free before delivery to the user.