There are a great many kinds of packing for piston rings, but the most commonly used at the present time are the steam packing rings. The character, accuracy in construction and condition of the piston make a great difference in the quantity of fuel consumed and the amount of power developed by the engine.
=The Piston Rod= connects the piston to the cross-head and is generally made of steel. Where the piston rod enters the cylinder, a steam tight joint is obtained by the use of a soft, pliable packing placed in the stuffing box, and held in position by the stuffing box gland.
This box is kept packed just tight enough to prevent leaking, by drawing up the stuffing box gland when required. This can be repeated until the packing is all used up, when box must be repacked.
=The Steam Chest= contains the valve, and can be on either side of cylinder as may best suit the style of engine. Steam is admitted into the steam chest, and passes into the cylinder by the action of the valve.
Many engine builders cast cylinder and steam chest in one piece, while others cast them separately and bolt them together. The only advantage of the former over the latter is the absence of one less joint to keep packed.
[Illustration: Steam Chest and Plain Slide Valve.]
The steam ports are the two openings through which the steam is admitted to the cylinder.
The exhaust port is the opening through which the exhaust or waste steam passes out of the cylinder.
There are a great many kinds of valves used on steam engines, namely, the Corliss, Slide, Rocker, Balance, Rotary, etc., but the one most commonly used on farm engines is the plain slide valve, which has been generally adopted by all the larger engine builders in this country. It is simple in design, and when properly set does its work very efficiently. They are less complicated than others and are easily set; they are made in many different designs, but the principle of each is the same.
The slide valve is constructed to slide upon the smooth surface of the valve seat, in which are contained the two steam ports for the admission of steam to each end of the cylinder, and also the exhaust port through which the exhaust or waste steam passes out of the cylinder.