A split-tube breathing valve. From The Department of Scientific and Industrial Research, Advisory Council, Second Report of the Mine Rescue Apparatus Committee, Published by His Majesty’s Stationary Office, 1920, page 31.
A split-tube breathing valve. From The Department of Scientific and Industrial Research, Advisory Council, Second Report of the Mine Rescue Apparatus Committee, Published by His Majesty’s Stationary Office, 1920, page 31.