68 



\M< HIM m: \\\ I 



\v 



/. -The form of packing used in the 



air jMiinj) l.u 57, is not suitable for st- <>ns. 



tli.- latt.-r the packing is now always metallic. The 

 sinipl. M t. .1-111 i f iiH-iiillir packing is that known as Ramsbot- 

 t.. IM'S. Thi.s form is very largely used for ! -oiu.it i\e pistons, 

 and for small pistons in many kinds of besides. A 



locomotive piston for un is inch cylindci \\ ith Knmsbottom's 



packing is shown in fig. 58. The 

 particular piston there illustrated 

 is made of brass, and is secured 

 to a wrought-iron piston rod l.y 

 a brass nut. Two circumferential 

 grooves of rectangular section an- 

 turned out of the piston, and into 

 these fit two corresponding rings, 

 which may be of brass, cast 

 or steel. In this example the 

 rings are of cast iron. These rings 

 are first turned a little larger 

 in diameter than the bore of the 

 cylinder (in this example inch;, 

 and then sprung over the piston 

 into the groves prepared for them. 

 Their own elasticity causes the 

 rings to press outwards on the 

 cylinder. At the point wl 

 ring is split a leakage of 

 will take place, but with <|uick 

 running pistons this leakage is un- 

 important. The points where tip- 

 rings are cut should be placed diametrically opposite, so as to 

 'diminish the leakage of steam. 



EXERCISE 59: Locomotive Piston. A part elevation an-1 part 

 section of a locomotive piston, for a cylinder having a bore 18 inches 

 in diameter, is shown in fig. 58. Draw this, and also a viewkx 

 on the nut in the direction of the axis of the piston de 6 



inches to a foot. 



. The reason why the part of the piston rod within the 



58. 



