Hard Disk Drive Air Filter

During the performance of the hard disk drive the speed of rotation of a spindle is very high (in modern models it is up to 15000 revolutions per minute), and the distance between a surface of a disk and a magnetic head varies from units to several parts of micron. The penetration of dust between a head and a disk can cause operation failure, and, most likely, the hard disk drive failure; therefore, the hard disk drive case is made almost hermetic. In order to adjust the pressure, the barometric filter connecting internal volume of hermetic zone with atmosphere is used. It is designed for cleaning the atmospheric air from dust and aggressive substances and consists of the mechanical filter intercepting dust, chemical absorbent (the activated coal) absorbing gases, and dehydrator (silica gel) absorbing moisture, and sometimes a selective polymeric membrane. The barometric filter is capable to intercept particles sized more than 0,3 microns that meets the standards of cleanliness of atmosphere in a hard disk drive. As hard disk drives are not completely hermetic devices, manufacturers specify above sea level altitude range in which they can save workability (usually from -300 to +3000 meters) for them as the height of flight of a magnetic head depends on air rarefaction.

During the operation of the hard disk drive the air stream circulating at a great speed due to the fast rotation of magnetic disks gets to the special filter trap, which is designed for cleaning the internal "atmosphere" from small particles of a drive working layer; despite all the taken measures, those particles, nevertheless, are crumbled from disks at flying ups and landing of magnetic heads. The filter trap also intercepts any other small particles, which can get in the hermetic block.