MODERN STEAM PRACTICE.

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fly wheels are fitted, thus less diameter is required for a givenweight, and it is found desirable to limit the weight to 1 ton. Whenthe means of transport is difficult no part of the engine shouldexceed this weight. These engines do not require massive andexpensive foundations; they can rest on balks of timber with merelya few bolts to hold them down. They can also be driven at a highvelocity, owing to the action of the valve preventing all blow andjar in the working, when the lap and lead are properly adjusted:a pair of them can be worked together, the cranks being at rightangles to each other, causing great uniformity in the flow of theblast, and no regulator is required. A pair of these engines, witha piston speed of 400 feet per minute blowing 3600 cubic feet ofair, make a very compact arrangement for small-power blowingengines.

HORIZONTAL BLOWING ENGINE.

Horizontal high-pressure blowing engines have been extensivelyused. In the following example (Fig.188), which is one of the largestdescription, the diameter of the steam cylinder is 4 feet 3 inches,with a stroke of 9 feet. The blowing cylinder has a diameter of108 inches, and the length of stroke is the same as for the piston ofthe steam cylinder, the number of strokes being about twenty-two,giving a total speed of 396 feet per minute.

The steam valves (Fig. 189) are of the piston type, which are verygenerally used for blowing engines, because they are perfectlybalanced, and therefore suffer little wear and tear, which is a greatdesideratum with engines requiring to go day and night for a length-ened period. The valves are cast together with a pipe connection,each piston is packed with a single ring, which is kept up to theworking face by a spring; the junk rings are each secured with asingle nut having a thread cut on the valve spindle, which is centralwith the valves. The valve casing is a circular casting; the steamis admitted between the valves, and the exhaust takes place at bothends. The valves are arranged so as to make the steam ports asshort as possible; and there is an annular ring round the piston, togive free entrance and exit for the steam all round the circumfer-ence of the valves. The valve rod passes through stuffing boxes atboth ends of the casing, and as the valves are placed at the side ofthe steam cylinder, the motion for working them is direct, a plain