LOCOMOTIVE ENGINES.

601

projections cast along with the spring rings. The body, junk ring,and packing rings, are of cast iron ; the bolts for the junk ringare screwed into brass nuts let into the body, the piston rod beingfirmly secured with a split cotter. There is a wrought-iron restpinned to the body, for keeping the body and packing rings centralwith the cylinder.

With the view of diffusing the pressure on the packing rings, apair of brass rings have been adopted cut at one point, inside ofwhich is a concentric spring ring, on which springs and set screwsare brought to bear, thus diffusing the pressure all round the pack-ing rings, and as these are of brass, the friction is thus reduced.The action of the concentric spring ring, in this case, differingfrom the foregoing examples, is needed, inasmuch as it acts ofitself as a spring keeping the two packing rings equally up to theface, which would not be the case were the small springs actingdirectly on the packing rings. The body and junk ring are of brass,the piston rod being fitted with a screwed end, which is screwedinto the piston, and has a pin passing through the body and rod.

In one of the examples under notice the piston is parallel, whilein the other one the body is deeper, thus giving a better hold forthe piston rod, and it will be noticed in both arrangements thatsnugs are cast on the body, through which the set screws for thespring pass. We consider that these pistons are excellent examplesof their dass, and the packing rings when of brass, as these are, willundoubtedly wear much longer than others.

Another very good method (Fig. 468) for diffusing the pressure, asapplied to single cut rings, is to have a circular Steel spring, bearinguniformly on the entire circumference of the packing rings, the springacting between the rings pressing them up to the surfaces of thepiston flanges, as well as the cylinder surface, and supplying of itselfthe necessary ränge of elasticity. The rings are cut obliquely on theirfaces, thus preventing grooves being cut in the cylinder surface;the piston rod in this example is secured by a plain cotter. Allpistons should be fitted with some means for preventing the boltsin the junk rings working backwards. A plate is shown in thisexample which bears on the side of the bolt heads; it issecured with two stud bolts, and two stud pins also pass throughit, having a split pin bearing on the top of the plate. All therubbing surfaces of these pistons are turned and rendered per-fectly steam-tight by scraping them; formerly they were ground