386

MODERN STEAM PRACTICE.

for double-ported valves, that is to say, there are two steampassages at each end, and one central passage, in communicationwith the condenser. The joints should be placed metal to metal,all planed or surfaced in the boring lathe, and the rubbing surfaces

Figs. 267-268.—Cylinder. 1

1—

;

for the slide valve should also be carefullyplaned as smooth as possible, and thenscraped to a face plate, before the slidevalve is fitted, which should also be care-fully faced on the plate, and thus bothsurfaces will only require a finishing touch.

All the other joints are made steam-tightby interposing a thin coating of red lead.

The joints being thus metallic, the work-ing of the engine has but little tendencyto loosen them, which might otherwisehappen were an elastic joint adopted. Onthe front end of the cylinder a central manhole must be left, for theboring bar to pass through; with single piston rods there is a smallcover with stuffing box and gland, but with double or more pistonrods a plain cover is fitted; holes are also left in the front end of thecylinder for the air-pump rod, with suitable glands and bushes, and ahole at the bottom for the relief valve; narrow fitting strips shouldbe left at those parts where the main framing abuts against theother fittings. The cylinders are bolted together, with Hanges placedbetween them, having narrow fitting strips all round, which are care-fully planed; all the holes should be drilled, and rimed out to make

1 a, Cylinder. b, Annular steam space. c c, Steam ports. d, Exhaust port. e, Exhaust branch.f f, Piston-rod glands. g, Cover for hole for boring bar.