Whistle to signal clogged air filter

A whistle to signal a predetermined clogged condition of an air filter comprising a first part having a flange adapted to engage a minute portion of the upstream side of a filter and a cylindrical extension from said flange adapted to extend through the filter medium;

• and a second part of disc-like form having snug removable interengagement with the downstream end portion of said extension and constituting a flange adapted to engage a minute portion of the downstream side of the filter and to compress the filter medium between said flanges;
• said parts defining therebetween a cylindrical chamber including axially spaced apart end walls each having a central orifice therethrough operative in conjunction with said chamber to emit an audible signal upon predetermined increase in pressure drop across the filter.