DUST AND ITS DANGERS 



339 



to be cleaned. Air pressure causes a strong current of air to 

 rush into the vacuum carrying dirt and dust with it. On its 

 way to the pump where the vacuum is produced, the dust- 

 laden air passes through a thick, closely woven cloth, or is 

 washed by a spray of water, thus removing all dirt and dust. 

 The air which actually passes through the pump is, therefore, 

 practically dust free. 



In the sweeper type (Fig. 239) the vacuum is produced by 



FIG. 240. 



bellows, or movable diaphragms, operated by the friction of 

 the wheels upon the floor or carpet. In this type of cleaner 

 the cleaning tool is a part of the machine itself. 



Many modern dwellings, churches, auditoriums, office 

 buildings, stores, and school buildings are equipped with 

 stationary vacuum cleaners. In such cases the machine is 

 usually located in the basement and the suction pipes are run 

 to the various rooms of the building. Rubber hose carrying 



