'USAAF, Detector Assembly, Demand Oxygen Mask Leak'. By Master Plastic Molding Corp. Approximately 3.5"/9cm diameter. This mechanical leak detector consists of two sections, a bottom, flat, plastic plate, and an upper, plastic shell bearing a female connector. The two are connected by collapsible rubber bellows. When an oxygen mask is placed on the face and the tube plugged into the tester, a completely closed system is created. By releasing the bottom plate to hang free on the bellows, a predetermined suction is caused, and if the mask has a leak, the plate will descend. The user's breath must be held as if swimming underwater. If the plate descends all the way in 10 seconds or less, a dangerous mask leak is indicated and remedial action would have been taken. AAF marked and with 1945 order code. Used with demand type masks including the A-14 as detailed in the AAF Reference Manual for Personal Equipment Officers. Unissued/unused condition. Stock code O24834.