My latest find is this German gas mask filter quality control machine ( Atemwiderstand Feldprüfer ).The quality of the filters could be verified with a special machine introduced on October 25th, 1916, it is basically a wooden box with a lid opened by a hinge.The two sides each have an opening to insert the standard filter to be verified at one end and a test filter (Vergleichseinsatz) which worked correctly at the other end.Two of these correctly working test filters were supplied with each box and marked with a diagonal yellow marking.In order to compare the pressure of the filter to be tested, a manometer operating with water was placed between the test filter and the standard filter.A pump forced air through the filters and the tester would look in which direction the water of the manometer went.(source Johan Somers Imperial German Field Uniforms and Equipment 1907-1918).
Enjoy the pictures.
Leftside a standard filter.
Rightside a test filter.
Matching numbers box and test filters 6863.
Leftside standard filter rightside test filter.
Enjoy the pictures.
Leftside a standard filter.
Rightside a test filter.
Matching numbers box and test filters 6863.
Leftside standard filter rightside test filter.
