Fill indicator for a vacuum cleaner dust collector

Claim 1

An indicator for visually denoting the amount of dust or dirt in a dust receptacle of a vacuum cleaner or the like comprising: a trasparent cylinder, a piston having indicia is rotatably journalled in said cylinder and communicating with the inlet of said dust receptacle that has a predetermined pressure, the outer surface of said cylinder being provided with marking for continually indicating the amount of filling of the dust collector, said piston being provided with a central shaft having a threaded end projecting from the forward end of said piston, a nut adapted to be screw-connected to said threaded end, and a diaphragm communicating with the outlet of said dust receptacle and fixed to said nut, the pressure difference between the inlet and outlet of said dust receptacle causing said diaphragm to effect a translating movement which causes the threaded shaft of said piston to turn within said nut thereby rotating said piston in said cylinder, a latching means on said piston and cylinder which co-acts to retain said piston in the position it has assumed in the cyliner due to said pressure difference, said latching means including a first row of teeth at the end of the piston remote from said diaphragm, a spring engaging said nut on the opposite side from the diaphragm and biasing said piston rearwardly towards said first row of teeth, and a second row of teeth on a surface of said cylinder facing said first row of teeth, said spring urging said first and second row of teeth into latching engagement when said vacuum cleaner is inoperative.