MODERN STEAM PRACTICE.

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diameter add yV inch to the thickness. The flanges for the coversshould be one-fourth more than the body; the ends and covers one-tenth more than the body. The ends and covers should be stronglyribbed with deep bars cast on, radiating from the centre; the depthof the covers, including ribs, should be about one-eighth of thediameter of the cylinder. For additional strength the body of thecylinder is cast with two or more deep rings, to which are securedthe rings of wood fastened to the lagging with ordinary screw nails.A manhole is cast in the covers of large cylinders, fitted with a lid;and the hole for the boring bar on the end of the cylinder is ofsufficient size to inspect the inside of the cylinder, and is also fittedwith a cover which can be easily removed. The thickness of thesides of the steam ehest varies from ^ inch for small to 1 ^ inchfor large diameters, and is strongly bracketed where required. Thesteam ports are divided by a central rib, but the exhaust port isleft free, so that the passage for the waste steam to the condenseris not interfered with. The exhaust is generally carried round thecylinder through a broad beit, but this depends entirely on thearrangement of the pipes leading into the condenser.

Double-ported valve .—The thickness of this valve for small sizesis $4 inch, ranging to 1 inch for larger sizes; and it is cast witha centre rib to strengthen it. The diameter of the annular spacefor receiving the metallic rings, for taking the pressure of the steamoff the back of the valve, should be as large as convenient; thedepth of the recess in the cover is found by multiplying the breadthof the rings by 2; the breadth of the rings ranges from 1*4 to 1^inch, their thickness being about $4 inch for large sizes, to ^ inchor more for extra sizes. The set screws are generally ^ inch indiameter, fitted with jam nuts and washers. The valve casing isan open casting varying from ^ to inch in thickness; theflanges for bolting it to the cylinder, and for the cover, may beinch more than the thickness of the sides. The steam pipe is atone end, and the steam passage tapering to the extreme end.

Piston rod and stuffing box .—To find the diameter of the pistonrod multiply the area of the piston by the full pressure in the boiler,to which add the vaeuum or 12 lbs. per square inch, and divide theproduct by 2240; the quotient gives the area of the rod in squareinches for compressive strain. For tensional strain where cottersare used, or where the piston is attached to the rod by a nut, divideby 4000, which gives the sectional area at the bottom of the thread.