Page:Motors and motor-driving (1902).djvu/303

Rh drives the crank direct through the connecting rod, exactly the same as in a petrol engine. is the flywheel, and a tap for letting dirty lubricating oil out of the crank chamber. Each of the four cylinders works in a precisely similar way to the one described. In some engines the valves are parallel with the cylinders instead of slightly inclined as shown in fig. 26.

Piston-rings.—These scarcely require description, as they are the same in principle as those used in petrol motors, and by turning to the chapter dealing with these the reader will be



able to find out how the piston, which must be a free sliding fit in the cylinder, is also pressure-tight.

Stuffing Boxes.—As the piston-rod issues from the bottom of the cylinder it is necessary that this should also be a free sliding fit, and at the same time steam-tight. These ends are attained by having a circular cavity, into which packing is inserted and held firmly by a screw ring or gland, and a locknut. Two forms of stuffing-box are shown in figs. 27 and 28. The packing usually consists of some substance in which asbestos and graphite are mainly used.

Condensers.— In damp weather, when using a full supply of