A special series of experiments1 to determine the metabolic rate (this is done by the collection and analysis of expired air) of subjects exposed to varying temperatures and humidities was conducted under the supervision of Dr. R. R. Sayers and Dr. W. J. McConnell as part of a cooperative study of the physiologic effects of atmospheric conditions being made by the Bureau of Mines and the American Society of Heating and Ventilating Engineers. In this work a number of different types of valves were experimented with in order to select the one best suited. The deciding factor in selecting a valve for use in basal metabolic work rests with its ability to prevent any small amount of air from escaping around the edges of the valve when closed, which may be designated as "slip leakage."
Several types of valves are available which, though satisfactory for use in certain breathing apparatus,
FULTON WB. AN IMPROVED AIR VALVE FOR APPARATUS USED IN BASAL METABOLIC WORK. Arch Intern Med (Chic). 1924;33(4):497–499. doi:10.1001/archinte.1924.00110280095009