248

MODERN STEAM PRACTICE.

is blown up the chimney) should be trapped at the end, by leadingit into a cast-iron cistern, fitted with a separate pipe into thechimney, having a bend at the end for directing the waste steamvertically; by this means much of the moisture is got rid of, beingretained in the cistern and run off by a suitable overflow pipe. Inthis way the chimney is kept comparatively dry, and consequentlyless liable to the deterioration caused by a blast of steam and waterblown into it. Some engineers prefer blowing off the waste steamdirectly from the cylinder by a vertical pipe passing throughthe roof of the engine house. By such an arrangement there is, ofcourse, no steam blast to injure the chimney; but, on the otherhand, we lose its valuable aid in urging the fires, by causing apartial vacuum in the chimney, which tends to supply through orbetween the fire bars the necessary quantity of oxygen to effectcomplete combustion.

The drums for the round wire ropes must be of large diameter.They are of two kinds, conical and parallel; with the conical thestrain on the engines is better regulated. The lift is taken on thesmallest diameter, and the rope unwinds for the empty cage fromthe largest diameter; consequently the latter balances in a measurethe ascending cage fully loaded, which is lifted slowly, throwingless strain on the tnachinery. The drums are constructed of lightcast-iron wheels, each with eight strong arms, and arranged forbolting together in two halves; a side Hange is cast on to receive thewooden battens, to which they are securely bolted. For the conicaldrums there are two wheels of the same diameter, one at each end,with Hanges bevelled according to the hollow given to the cone,and a smaller wheel is placed between them, having a flat rim; thewood is laid quite flat on the inside, and for the outer diameter it iscut to the cone required. The wire ropes are put on one aboveand another below the drum, and are wound from its longitudinalcentre, the cone increasing to the ends at each side. The side andmiddle sheaves are keyed on the shaft similarly to an ordinaryHy wheel, and should be fitted with wrought-iron rings, shrunk onthe outer circumference of the bosses. It is preferable to fit a flywheel close up to the main bearing; it should be of sufficient weightfor the engine, and made of extra strength in the arms, as thebrake is generally applied on the periphery.

The most approved form of brake consists of wooden blocksfastened to wrought-iron hinge pieces, vibrating on pins and joints,