Top Considerations in Specifying a Magnetic Rotary Seal
Rotary Magnetic Seals, or "Liquid O-Rings" are commonly used in vacuum systems to effect a seal of a part that has rotational movement such as a motorized shaft or a manual shutter.
Keep the following in mind when making your selection:
1) Avoid additional magnetic field effects in your chamber as much as possible: some ferrofluid type seals produce 180 Gauss or more, which will often have an effect on your process. Look for less than 20 Gauss.
2) Look for high pressure capacity: the higher the pressure capacity, the higher the life of your seal. A rating of 2 atmospheres minimum.
3) Make sure you get a shaft with high torque transmission capacity: without it your rotary seal will be prone to shaft breakage or to seal failure due to excessive torque or side loads.
4) Look at where the seal stages are located: Some ferrofluid seals have stages cut in the stator, which reduces the shaft diameter by as much as 0.08".
5) Look for a seal that can be rebuilt in the field: some ferrofluid seal magnetic circuits discharge upon disassembly, thus requiring re-charging of the seal magnets after re-assembly.
6) Watch out for problems with external magnetic fields: find a seal that can operate reliably in >500 Gauss external magnetic fields without seal degradation.
7) Size: compare performance, and then compare size. Well designed magnetic rotary seal elements will be small to allow for larger bearings to be installed, resulting in longer seal life.
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