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32 The "Sturtevant" System of Drying Timber.

Rapid and efficient drying is effected by subjecting the timber to a continual passage of warm dry air in a kiln constructed of wood or brick into which hot air is introduced by a fan. Fig. 128 shows a sectional view. The air is first heated by a Sturtevant heater to the desired temperature by either live or exhaust steam, which ensures that the temperature never exceeds 212° F. Then, by means of the fan, it is forced through the outlets of the supply duct  into the kiln, circulating completely round the timber. Owing to the high temperature of the air it rapidly absorbs moisture and is then passed into the atmosphere, or it may be returned to the apparatus to be reheated and the absorbing process repeated. The return ducts and  serve a double purpose by utilising the remaining air which comes gradually laden with moisture; the process of reheating serves, by regulation, to maintain any desired degree of humidity within the kiln, and thus prevents the exterior of the stack drying too quickly and becoming simply skin dried. Perfectly green coniferous timber one inch thick can be dried within six days, other thicknesses in proportion. It is claimed that by this process the outside of the wood is kept open, which allows the moisture from the heart to escape without splitting, warping, or discolouring taking place. Fig. 129 is a sectional view of a large kiln having four compartments. Timber is erected in stacks, on trucks running on rails, and is thus easily conveyed in and out of the kiln.

Fig. 130.—Erith's Patent Automatic Drying Kiln, General View.

Erith's Patent Automatic Timber Drier.

These kilns may be of wood or brick. For carrying out this system of drying timber one form of kiln is shown at Fig. 130. The timber is conveyed into the kiln by being stacked upon trucks running on rails, and as the timber is dried, it is passed out at the opposite end. A canvas roller door is provided at each end which works on the roller-blind principle, but fitting almost air-tight. This system dries wood