Motion feedthrough for vacuum chambers: rotary and linear feedthroughs that carry rotation or travel through the chamber wall on a ferrofluid seal, a magnetic coupling or a welded bellows
Turning or pushing something inside a vacuum chamber from outside · ferrofluid-sealed shafts, magnetically coupled drives through a closed wall, and welded-bellows linear and rotary feedthroughs, compared by seal, bake, torque, force and life
Electrical pins pass through a vacuum wall in a sealed insulator; motion cannot. To rotate a substrate holder, open a shutter or push a sample into position, the feedthrough has to move a shaft while keeping the leak rate at UHV levels. Three constructions do this. A ferrofluidic feedthrough runs a solid shaft through rings of magnetic liquid. A magnetically coupled drive turns a magnet outside a closed thin-walled can and drags an inner magnet with it, so nothing passes through the wall at all. A bellows feedthrough welds a flexible metal bellows between flange and shaft and flexes it for each movement. They differ in torque, speed, bake temperature, and in what wears out.
Rotary and linear motion feedthroughs that pass mechanical movement into vacuum chambers: ferrofluidic (magnetic-fluid) rotary feedthroughs, magnetically coupled rotary and linear drives, bellows-sealed and edge-welded-bellows linear and rotary devices, with their flanges, torque or force, speed, bake temperature, leak rate and cycle life. Multi-pin electrical feedthroughs for vacuum and hermetic enclosures are covered on the Electrical feedthrough (vacuum and hermetic) page; chamber shells and their CF ports on the Vacuum chamber body page; door hinges on the Vacuum chamber door hinge system page; viewports and shutters on the Viewport assembly for vacuum coating chambers page; process and test vacuum chambers on the Vacuum chamber page.
CNFX editorial research · Sources checked October 13, 2026 · 7 sources
Ferrofluid, magnet or bellows: what each construction gives up to get motion into the chamber
The choice turns on whether a solid shaft may cross the wall, whether the device must survive a high bake, and whether the motion is continuous rotation or a limited stroke. The makers' own figures set the limits:
The trade-offs follow from the construction. A ferrofluidic feedthrough keeps a solid through-shaft, which Ferrotec says transmits 100 % of the engineered torque in phase, without backlash or slip, but its fluid limits temperature and gas compatibility. [3][2] A magnetic coupling has nothing crossing the wall and no organic materials, which UHV Design ties to its 250 °C bake and its use in cleanrooms and magnetically sensitive instruments (with magnetic shielding); its torque is set by the coupling, and its zero-backlash claim is limited to low load and acceleration. [4] A bellows flexes on every stroke, which is why its life is stated in cycles. [5][6]
The picture above shows the arrangement these figures apply to: a large flange on a stainless chamber carrying a multi-pin electrical feedthrough, a small tube feedthrough and a shaft-type motion feedthrough with a bellows section, mounted on a bracket outside the chamber.
Construction
How the vacuum is kept
Figures stated by the maker
Ferrofluidic rotary feedthrough (Ferrotec)
Rings of magnetic fluid held by a permanent magnet and two pole pieces in the radial gap around a magnetically permeable shaft, each ring a liquid O-ring
0.2 atm (200 mbar) per stage (typ.); 10⁻¹¹ std cc He/s; uncooled −6 to 80 °C; shaft run-out ≤ 0.076 mm; dN up to 500,000 [1][2][3]
Single-piece vacuum enclosure; outer magnets drive inner magnets through it, with no bellows, fluids or dynamic seals
Bakeable to 250 °C with magnets in place; 0.45/1.8 Nm on CF16 and CF40 (MD16, MD40N/A); 9 Nm break-away on CF40 (MD40); 25 Nm on CF64 (MD63) [4]
Magnetically coupled linear shift (UHV Design)
Magnetic coupling along the axis through a closed tube
Axial coupling up to 90 N; speeds up to 1,000 mm/s [7]
Bellows-sealed linear shift (UHV Design LSM)
Metal bellows between flange and moving carriage
CF35 to CF150 flanges; strokes up to 1 m; 10,000-cycle lifetime guarantee, 3 million-cycle option; bakeable to 250 °C [5]
Edge-welded bellows linear drive (UHV Design ALBD)
316L edge-welded bellows
34 mm (1.33 in) CF flange, or 70 mm (2.75 in) with strokes up to 150 mm; 0.01 mm resolution; 10,000-cycle minimum life [6]
State whether the motion is continuous rotation, indexed rotation or linear stroke, the torque or force at the vacuum side, speed, bake temperature, flange size, and whether magnetic fields or any organic material are acceptable in the chamber.
02
Sizing a ferrofluidic feedthrough: stages against the pressure difference, an estimated 10⁻⁹ Torr, and dN against shaft speed
Ferrotec's ferrofluidic feedthroughs use multiple rings of ferrofluid held in stages formed by grooves in the shaft or pole pieces. A single stage sustains a pressure differential of 0.2 atm, 200 mbar (typ.), and the capacity of the whole feedthrough is approximately the sum of its stages. [1]
Editorial calculation, with an example pressure difference: holding atmosphere (1,013 mbar) against vacuum at 200 mbar per stage needs 1,013 / 200 ≈ 5.1, so at least six stages; a seal that also sees a 1 bar gauge purge on the atmosphere side (example value) would need 2,013 / 200 ≈ 10.1, so at least eleven. [1]
Ferrotec's ordering guide lists, for its feedthroughs (not every model shares every value; check the model data), a vacuum of 10⁻⁹ Torr, marked as an estimated value that depends on pumping speed and other gas loads, and a leakage rate of 10⁻¹¹ std cc He/s, noting that units are not regularly tested to that level. Uncooled units run at −6 to 80 °C (20–210 °F); water-cooled units may exceed this, and Ferrotec quotes a 150 °C bake that does not cover every unit, so the bake rating has to be confirmed per model. Housings are 300-series stainless (ISO 1.4301 or similar), shafts 400-series or 17-4 PH stainless, and shaft run-out is limited to 0.003 in (0.076 mm). The standard fluid suits inert gases; reactive gases may need a fluorocarbon-based ferrofluid. [2]
On speed, Ferrotec states that configurations perform at dN values of 500,000, where d is the shaft diameter in mm and N the speed in rpm, equal to 20,000 rpm for a 1 in shaft. [3] Editorial calculation: 25.4 mm × 20,000 rpm = 508,000, consistent with the stated dN; with the same limit, a 50 mm shaft (example value) would be held to 500,000 / 50 = 10,000 rpm. [3]
Inert gas; fluorocarbon ferrofluid for reactive environments [2]
Give the pressure on both sides of the seal, shaft diameter and speed, temperature at the seal, process gases, bake temperature and whether water cooling is available; ask how many stages the design uses and how leak rate was tested.
03
Magnetically coupled and bellows drives: 250 °C bake, break-away torque from 0.45 to 25 Nm, and life counted in cycles
Where a shaft seal is not acceptable, UHV Design's MagiDrive rotary feedthroughs transmit rotation through a single-piece vacuum enclosure by magnetic coupling, with no bellows, fluids or dynamic seals, for manual, motorised or automated operation. [4]
The torque available rises with flange size: 0.45/1.8 Nm for the MD16N/MD16A on a CF16 flange and the MD40N/MD40A on CF40, 9 Nm break-away for the MD40 on CF40, and 25 Nm break-away for the MD63 on CF64; the MD40 and MD63 bake to 250 °C without removing the outer magnets. Hollow versions can be stacked as concentric drives. [4] UHV Design describes the magnetically coupled design as fail-safe, with no risk of mechanical failure or leaks; the break-away torque it quotes is the figure to set against the load's starting torque. [4]
For linear motion, UHV Design's magnetically coupled linear shifts reach up to 90 N axial coupling and 1,000 mm/s, and are offered for high-duty-cycle uses such as shutters on production deposition systems. [7] Its bellows-sealed linear shift mechanisms cover CF35 to CF150 flanges and strokes up to 1 m, with a demountable bellows assembly, a 10,000-cycle lifetime guarantee (3 million-cycle option) and a 250 °C bake, and its edge-welded ALBD drives give 0.01 mm resolution with 316L bellows and strokes up to 150 mm on a 70 mm CF flange. [5][6]
Editorial calculation, with example duty figures: a shutter that opens and closes once every 10 minutes around the clock makes 6 × 24 × 365 ≈ 52,600 cycles a year, more than five times the 10,000-cycle bellows guarantee, which is why the 3 million-cycle bellows option or a magnetically coupled shift fits that duty. [5][7]
For a magnetic drive, ask for the break-away torque or axial coupling force against the load's start-up torque or force; for a bellows drive, ask for the guaranteed cycle life at your stroke and whether the bellows is demountable.
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Feedthrough details to send
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Motion: [continuous or indexed rotation; linear stroke]
Load: [torque or force at the vacuum side; speed; duty cycles per day]
Vacuum: [pressure on each side; leak rate required; gases]
Temperature: [operation; bake]
Flange: [CF size or other; orientation]
Drive: [manual, motorised, pneumatic; encoder]
Limits: [magnetic field; organic materials; particles]
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
How much pressure can one ferrofluid stage hold?
Ferrotec gives 0.2 atm (200 mbar) per stage (typ.), and the capacity of the feedthrough is approximately the sum of its stages. [1]
How fast can a ferrofluidic rotary feedthrough turn?
Ferrotec states configurations perform at dN values of 500,000 (shaft diameter in mm times rpm), equal to 20,000 rpm for a 1 in shaft. [3]
Can a magnetically coupled rotary feedthrough be baked?
UHV Design's MagiDrive feedthroughs are bakeable to 250 °C including the magnets, and the MD40 and MD63 can be baked without removing the outer magnets. [4]
How long does a bellows-sealed linear feedthrough last?
UHV Design guarantees 10,000 cycles for its bellows-sealed linear shifts, with a 3 million-cycle option, and a 10,000-cycle minimum for its edge-welded ALBD drives. [5][6]
Sources and what still needs a direct check
Sources checked 2026-10-13. Seven sources from two publishers: three Ferrotec pages on its ferrofluidic seals (how the seal works, ordering-guide specifications and seal benefits) and four UHV Design product pages (Solid MagiDrive rotary feedthroughs, bellows-sealed linear shifts, edge-welded bellows linear drives and magnetically coupled linear actuators).
