Hermetic Bellows: The Air-Tight Assembly Critical to Many Industries


Hermetic seals are imperviable devices designed to isolate the sealed product from unwanted exposure or contamination. These air-tight assemblies are critical when sealing in clean room situations or when compliance with EPA clean air regulations or personnel safety is necessary.

Here are a few of the applications and industries where hermetic bellows devices have proven to be the optimum design solution.

  • Filter Dryers which require a gas-tight seal when used in conjunction with CFC and HCFC refrigerants
  • Freeze Dryers which conduct lyophilisation (cryodesiccation) in vacuum environments with high purity standards
  • Compressors can utilize hermetic bellows valves to eliminate leakage past dynamic seals. Compressors can also use valve stem seals when there is a need to hermetically contain the shaft while allowing for axial shaft movement
  • Hermetic bellows devices have been used to prevent cavitation in Volume Compensators when the system’s positive pressure must be maintained during any volume fluctuations
  • Hermetic bellows can act as a piston in hydraulic or pneumatic Actuators to transform pressure to linear motion. They are particularly effective in high pressure applications where a dynamic seal could fail.
  • Vibration Dampers may employ hermetic bellows to isolate vibration.
  • Semiconductor and Aerospace technologies utilize extreme vacuum systems which may incorporate manipulators or linear translators, corrosive chemical washes, high-energy plasma etching, wafer production, and intense electromagnetic radiation in their manufacturing processes. Most of these activities take place inside sealed areas called clean rooms with hermetic equipment to drastically minimize personal and environmental exposure.
  • Hermetic bellows devices provide a layer of environmental protection when handling certain Energy Generation operations – including radiation, toxic emissions, and carcinogenic by-products. Hermetic bellows are also used in sealing scenarios involving extreme pressures and temperatures.
  • Hermetic bellows devices are necessary in Pharmaceutical Processing when biohazardous material must be contained and micro – contamination of must be eliminated.

What are some definitive features of a Hermetic Bellows design?

  • No elastomers to wear or replace
  • All metal, corrosion resistant wetted surfaces
  • Accurate positioning to address column instability (or “bellows squirm”)
  • Leak tight to 1 x 10-9 scc/sec
  • Compact nesting capabilities which allow for compression strokes up to full percentage of the free length

How do Flexaseal’s Hermetic Bellows stand out?

Flexaseal has designed and manufactured hermetic bellows devices for many of the applications and industries listed above. We utilize a wide array of metallurgies including various Hastelloy™ and Inconel® grades, titanium and Monel®. We feature flexible diaphragms, plates in varying thicknesses, full spring rate testing, and state-of-the-art machinery which enables us to produce a diverse range of fixtures and end fittings. Our welding department works closely with our engineering staff to control the manufacturing of all bellows cores, from stamping sheets of foil stock to pressure-testing the completed assembly. We use the TIG (Tungsten Inert Gas) welding process which provides the finest control of the weld arc, resulting in efficient, clean, and long-lasting welds. Once welded, 99% of our hermetic bellows are leak tested with Helium tracer gas, using the most stringent protocols.

To learn more about our capabilities and to see if your difficult sealing challenge can be solved by applying a hermetic bellows device, please contact applications@flexaseal.com or call 1-802-878-8307.