Dirt accumulation indicator for air intake filters

A device for the visual indication of dirt accumulations on air intake filters of air aspirating machines in the form of a reading which reflects the negative pressure in the clean air space of the air intake filter, the device comprising in combination:

• a generally pot-shaped indicator housing having a vertical center axis, a housing bottom, a housing side wall, and an open upper end;
• a cover attached to the open upper end of the indicator housing, the cover defining a window of transparent material occupying at least a portion of the surface of the cover;
• an indicator dial arranged underneath the cover, at a distance therefrom, so as to define a pointer gap between the cover and the indicator dial;
• a diaphragm piston arranged in the indicator housing for axial displacements along the housing center axis, the diaphragm piston dividing the interior space of the indicator housing into a negative pressure chamber between the lower side of the piston and the bottom wall of the indicator housing and a drive chamber on the upper side of the piston, the negative pressure chamber being in communication with the clean air space of the air intake filter, and the drive chamber being under atmospheric pressure;
• a piston return spring of the compression spring type arranged between the diaphragm piston and the bottom wall of the indicator housing, the piston return spring biasing the diaphragm piston axially upwardly, in opposition to piston displacements produced by a lowering of the pressure level in the negative pressure chamber;
• a vertical indicator shaft arranged inside the indicator housing and journalled in the housing center axis;
• an indicator arm attached to the indicator shaft, the indicator arm carrying a pointer which is arranged to reach into said pointer gap;
• a bell crank arranged in the drive chamber of the indicator housing on a horizontal pivot axis which is located at a lateral distance from the housing center axis, the bell crank having a long arm extending substantially vertically upwardly and a short arm extending substantially horizontally to the center of the diaphragm piston, into driving engagement with said piston;
• gear teeth on the upper end of the long arm of the bell crank forming a gear segment about the bell crank pivot axis;
• a pinion on the indicator shaft cooperating with the gear segment on the bell crank to translate angular displacements of the bell crank into magnified angular displacements of the indicator shaft and its pointer;
• a bell crank spring biasing the bell crank in the pivoting direction towards the diaphragm piston, so as to apply to the diaphragm piston a preload which is opposed to and smaller than the bias of the piston return spring;
• and
• means for adjusting the bell crank spring from outside the indicator housing, so as to adjust its preload on the diaphragm piston.

A device for the visual indication of dirt accumulations on air intake filters of air aspirating machines in the form of a reading which reflects the negative pressure in the clean air space of the air intake filter, the device comprising in combination:

• a generally pot-shaped indicator housing having a vertical center axis, a housing bottom, a housing side wall, and an open upper end;
• a sleeve-like housing insert arranged concentrically inside the indicator housing, the housing insert including a diagonal cross member;
• a cap-like cover of transparent material attached to the open upper end of the indicator housing, the cover having an axially downwardly extending central hub portion;
• a cap-like indicator dial having a top wall and an adjoining side wall, the indicator dial being attached to the hub portion of the cover in a concentric, axially and radially spaced relationship to the cover, so as to define an annular pointer gap between the cover and the indicator dial, the pointer gap including an axial gap portion which is open to the indicator housing on its lower end and a radial gap portion which extends radially inwardly from the upper end of the axial gap portion;
• a vertical indicator shaft arranged inside the indicator housing, the upper end of the indicator shaft being journalled in the hub portion of the cover and its lower end being journalled in the cross member of the housing insert;
• a horizontal indicator arm attached to the indicator shaft, the indicator arm carrying two pointers in diametrically opposite relation to the indicator shaft, the two pointers being arranged to reach upwardly into said pointer gap with parallel vertical length portions and adjoining horizontal length portions;
• a diaphragm piston arranged in the indicator housing for axial displacements along the housing center axis, the diaphragm piston dividing the interior space of the indicator housing into a negative pressure chamber between the lower side of the piston and the bottom wall of the indicator housing and a drive chamber on the upper side of the piston, the negative pressure chamber being in communication with the clean air space of the air intake filter, and the drive chamber being under atmospheric pressure;
• a piston return spring of the compression spring type arranged between the diaphragm piston and the bottom wall of the indicator housing, the piston return spring biasing the diaphragm piston axially upwardly, in opposition to piston displacements produced by a lowering of the pressure level in the negative pressure chamber;
• a bell crank arranged in the drive chamber of the indicator housing on a horizontal pivot axis which is located at a distance from the housing center axis, the bell crank having a long arm extending substantially vertically upwardly and a short arm extending substantially horizontally to the center of the diaphragm piston and into driving engagement with said piston;
• gear teeth on the upper end of the long arm of the bell crank forming a gear segment about the bell crank pivot axis;
• a pinion on the indicator shaft cooperating with the gear segment on the bell crank to translate angular displacements of the bell crank into magnified angular displacements of the indicator shaft and its pointers;
• a substantially horizontally oriented bell crank spring of the tension type having one extremity attached to a spring arm on the bell crank pivot axis, at a point located radially between the pivot axis and the gear segment and extending in in the same general direction as the small pivot arm of the bell crank, so as to bias the small pivot arm against the diaphragm piston and to apply to it a preload in opposition to the bias of the piston return spring;
• a spring adjustment pin rotatably arranged in a vertical bore of the housing insert, the spring adjustment pin carrying a radially extending spring arm to which the other extremity of the bell crank spring is attached and including means for securing the spring adjustment pin in any one of a number of angular adjustment positions;
• an opening in the wall of the indicator housing in the area of the lower extremity of the spring adjustment pin for access thereto with a pin adjustment tool;
• a ratchet wheel segment connected to the bell crank, the ratchet wheel segment having ratchet teeth arranged concentrically to the teeth of the gear segment;
• a pointed ratchet pawl extending downwardly from a pivot axis which is arranged parallel to and vertically above the bell crank pivot axis, on the opposite side of the housing center axis, and means for biasing the ratchet pawl towards the ratchet wheel segment, so that the point of the ratchet pawl engages a gap between two ratchet teeth at an inclination to said teeth at which angular movements of the ratchet teeth past the tip of the spring-biased ratchet pawl are possible only in a downward direction;
• a reset button protruding upwardly from the cover and extending downwardly into the indicator housing, the reset button being guided for vertical movements and biased upwardly into a rest position;
• and
• a reset arm extending horizontally from the ratchet pawl pivot axis to a point underneath the lower extremity of the reset button so that, when the reset button is depressed, it engages the reset arm, moving it and the attached ratchet pawl away from the ratchet wheel segment, thereby freeing the ratchet wheel segment and the connected bell crank for the execution of a return movement.