IN the course of experiments on coal-mine ventilation factors which the Bureau of Mines has been conducting for the past two years at its experimental mine near Bruceton, Pa., tests were made in order to determine the leakage of two air-locks which had been placed in the mine.
Each air-lock consisted of two doors, set in concrete frames and closed fairly flush with the door-jams.
The main source of leakage was along the sill where there was a narrow clearance opening, in addition to 4 to 6-inch gaps at the rails. However, this source of leakage was reduced somewhat by 6-inch canvas strips nailed to the bottom of each door on the pressure side. These doors represent minimum leakage under mine conditions. The results showed that with both doors closed at both air-locks, the leakage was 3.5 to 8.1 per cent. : one door closed at each airlock, 5.2 to 13.0 per cent. ; seal at outer air-lock, both doors closed at inner air-lock, 0.7 to 3.7 per cent.; seal at outer air-lock, one door closed at inner air-lock, 2.1 to 4.2 per cent.
An average leakage of 2 to 3 per cent. would seem to be a minimum for the best of mine doors under moderate pressure conditions, even with what would ordinarily pass for a good door and frame; lack of efficient provision along the sill-such as wet canvas flaps-may easily permit leakages of 5 to IO per cent. Further details are given in Serial 2602 recently issued.