. American ENGINEER and Railroad journal . nch Allen valve isréellement mieux qu'une valve Allen de 20 pouces dans la mesure où la vapeur ne peut donc pas être attribuée à l'action du jeu. Il semble très probable que la sprint des parties de la valvegiar avec les grandes valves est à blâmer pour une partie de la différence.les ouvertures de port à des coupures courtes sont très étroites, et les variations d'oscillation dans le fonctionnement de la valve, le mouvement, qui sont verysmall en eux-mêmes, serait grand en proportion de l'ouverture totalport de la vilve. Le professeur Goss a fait la démonstration de thaton le • Schenectady avec la comparaison
1847 x 1353 px | 31,3 x 22,9 cm | 12,3 x 9 inches | 150dpi
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. American engineer and railroad journal . nch Allen valve isactually better than a 20-inch Allen valve as far as the steam cannot, therefore, be attributed to the action of clearance. Itseems very probable that the springing of the parts of the valvegear with the large valves is to blame for some of the difference.The port openings at short cut-offs are very narrow, and slightvariations in the working of the valve, motion, which are verysmall in themselves, would be large in proportion to the totalport opening of the vilve. Professor Goss has demonstrated thaton the • Schenectady with comparatively low boiler pressurethe variation of the port opening was 30 per cent, of the average, which of itself would be great enough to produce an exten-ivechange in the character of the indicator cards, and consequentlyiu the mem effective pressure. The effect of insufficient lubri-cation of valves was very clearly shown by Mr. E. M. Heir in apaper read before the .Western Railway Club and reproduced on R£VOLU TV OA/5 /^f7? A//A/ (J T£.. V&tres are designated thus:20 plain ral^e 20 dfl/en ra/ve /6rfllen yalre --. Jfbte•■■- /n a/l tests length ofport corresponded to lengthof yd I re. Tests Comparing Laro-e with Small Locomotive Valves. pressure is concerned, but the road experience and the results onthe testing plant show that the shor er valve is as good as thelonger one. From an inspection of the indicator diagrams it doesnot appear that the back pressure is materially affected by theshortening of the port, and one reason why the 16-inch Allenvalve in general does better than the 20-inch plain valve and aswell as the 20-inch Allen valve may be that the area of the admis-sion ports to the earlier cut-offs is capable of supplying all of thesteam that can get through the pipes or ports. Surface condensation might be blamed as the cause of some ofthe loss from large ports, and with the large amount of metalnear by to conduct the heat away some may be tempted to dis-trust
