VENTILATION 



73 



Fig. 11.— Simple 

 extraction cowl 

 (Parkes). 



In all cases the introduction of stall divisions interferes 

 materially with the thorough perflation of air ; the incom- 

 ing current strikes the stall division and goes 

 over it. In this light stall divisions can only 

 be regarded as an objection from a sanitary 

 point of view, so that the introduction of bails 

 in industrial and military stables has some- 

 thing more than economy to recommend it. 



Ventilation by windows in the type of stable 

 described is the most perfect that can be pro- 

 duced, though the open ridge as an outlet 

 leaves something to be desired ; short exhaust 

 tubes of good diameter with fixed extraction 

 cowl, would probably be preferable for small 

 stables, and prevent down draught. 



Tubes, Air-Shafts and Cowls. — The most simple form of 

 exhaust or extraction tube is that seen in Fig. 11. Around 

 the top of the tube is a collar or flange sloping downwards ; 

 covering the tube, but at some height above it, is a conical 

 cap supported on uprights. Air currents impinge on the 

 flange, and passing across the mouth of the tube produce 

 an aspiratory effect. If the structural mechanism of this 

 cowl be reversed, an inlet or downcast tube is produced 

 (Fig. 12.) 



Cowls for covering tubes are of many 



kinds, the most familiar perhaps being the 

 lobster back made with a vane, either to open 

 towards the wind if intended as an inlet, or 

 away from it if an outlet. 



But there is a serious disadvantage attached 

 to all such cowls, they depend on their 

 mechanism keeping in perfect order, and ex- 

 perience shows they are very liable to derange- 

 ment. A fixed cowl is best, and of these 

 Inlet there are many in the market. Fig. 13 is a 

 Boyle extractor, the mechanism of which may 

 be seen in section, Fig. 14. 'A' indicates the opening 

 into which the wind passes, and impinges upon the deeply- 



Fig. 12. 

 cowl (Parkes). 



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