<P> Vacuuming is performed in the same manner as with a portable machine . Sometimes, the higher vacuum power of central vacuum may require reduction (for example, when cleaning a delicate sheer fabric curtain). Excess vacuum is "bled off" by partially opening a bleed port or slot to let some intake air bypass the cleaning tool . The bleed port is usually located at the tool end of the vacuum hose, to allow quick adjustment during use . </P> <P> When cleaning is complete, the vacuum hose is removed from the wall inlet (which snaps shut and shuts down the vacuum motor). The hose is coiled up and hung on a storage rack, and any cleaning accessories are stowed away . </P> <P> Cyclonic and filtered central vacuum systems are the two main types of central vacuums, differentiated by the method used to separate dirt and dust from the incoming airstream . </P> <P> True cyclonic cleaners do not use filtration bags, instead separating the dirt and dust into a detachable cylindrical collection vessel or bin . Air and dust are sucked at high speed into the collection vessel at a direction tangential to the vessel wall, creating a fast - spinning vortex . Roughly speaking, the dust particles and other debris spiral outward to the wall of the vessel by centrifugal force, where they fall due to gravity into the bottom of the collection bin . For a more complete technical description of this process, see the article on "Cyclonic separation". </P>

What function do the metal rings serve in the vacuum cleaner hose