Devices for visually indicating the amount of dust and dirt present in a vacuum cleaner dust bag or container are known. Most often these devices depend upon the difference in pressure between the outside of the vacuum cleaner and the inside of the dust container in order to displace or rotate an element within a sealed casing. The movement of the element corresponds to the degree of filling of the dust container. Devices of this type have a serious disadvantage in that they require the use of sealing rings and specially designed air filters in order to insure the dependable functioning of the indicating device. Naturally, the use of sealing means and filtering devices increases the cost of manufacture of the above-mentioned indicating devices, as well as requiring periodic inspection in order to insure the faultless operation of these indicators.
USPTO Backgrounds
USPTO Backgrounds