240

MODERN STEAM PRACTICE.

reduce the diameter of the cylinder and length of stroke of thepiston, and so to drive the engine shaft at a greater number ofrevolutions than the drum shaft. The old type of engine most infavour is of the beam description, vibrating on a gudgeon on pillowblocks supported by a single column, having plain cast-iron guides,with crosshead and link attachment connecting the piston rod withone end of the beam; this being the simplest arrangement for givinga true vertical motion to the piston rod. The other end of the beamis connected to the crank shaft by a cast-iron connecting rod, ofsufficient weight to balance the piston and its adjuncts. Theserods are fitted with wrought-iron straps and brass bushes, with jibsand keys for adjusting the brasses. The bed plate for carrying thecylinder, main column, and pillow block for the crank shaft is castin one piece. When the bed plate is securely bolted down on an evensurface, with a firm foundation, this form of engine is very strong anddurable, and is generally constructed on the high-pressure principle.Horizontal geared engines, however, have in a great measuresuperseded those of the vibrating beam type. They are certainly verycompact, and when properly proportioned give great satisfaction,notwithstanding the objections arising from their wheel gearing.

The DIRECT-ACTING HORIZONTAL ENGINE, with the drum forthe wire rope placed on the crank shaft, may be regarded as the typeof engine to be used for the future. Simplicity is the object to beattained, and we attain it in the direct motion of this engine simplyby giving a little more diameter of cylinder and a longer pistonstroke, with a certain number of revolutions to suit the diameterof the drum and the speed usually allowed for running the wireropes. Although single engines are in daily use, they are better tobe used in duplicate, with one crank shaft, and cranks at rightangles to each other. With the latter form there is no difficultyin starting, as is sometimes the case with single-cranked engines,which have a tendency to stop on the dead centre, or extreme endof the stroke, and require great attention on the part of the attend-ant to prevent this occurring. This objection is entirely removedby coupling the engines at right angles, the one assisting the otherin the extreme position. The perfect ease and certainty with whichthese engines can be handled by means of the beautiful link motionand double eccentrics—combined with the powerful brake on theperiphery of the fly wheel—renders the direct-acting horizontalengine a great boon to the practical miner.