STATIONÄRY ENGINES.

161

The economy of the single-acting pumping engine depends on thehigh steam pressure adopted—the higher the pressure in the boileris the less water is required to be evaporated or boiled off propor-

Fig. 97.—Bücket.

a, Bücket, b, Leather disc. c c, Top and bottom plates. d d, Gutta-percha rings, e, Holes forwater pressure for the packing rings, f, Rod. g, Cross bar for securing the rod with jib andcotter.

tionally; and, in addition, the facility of cutting off the steam at anypart of the stroke to suit the load on the engine, and the careful cloth-ing of all the parts where radiation takes place with a non-conductingmaterial, keeping those parts warm and the surrounding atmospherecool. To effect this the cylinder is surrounded with a steam casingor outer cylinder. Steam is admitted between these two, and theouter one is covered with feit and wood over all, and in some casesbrickwork; the cylinder cover is hollow, admitting steam, and it isprotected with wood lagging , as it is technically termed. The