| 摘要 |
A filter medium for use in a vacuum cleaner is shown with external brush means which is movable across the filter face for cleaning the soil therefrom. The brush means may either be moved manually, by automatic controls, by time switches, by pressure differentials operating in a piston-cylinder arrangement, or by a pressure indicator unit which monitors the clogging condition of the filter. Moreover, control means are provided for protecting the vacuum cleaner drive motor from damage from liquids when liquids may be drawn into the vacuum cleaner. |
