PISTON AND ROD.
The Piston is another very important part in the construction of an engine, and it conveys the power of the steam to the crank. It is composed of a piston head, on which are placed the piston rings held in position by the follower plate, and is securely attached to the piston rod. Great care should be taken in the construction of the piston rings to have them fit the cylinder perfectly tight, at the same time to have the least possible friction. Piston rings should always be made of a softer metal than the cylinder so that the greater part of the wear will be upon the rings instead of the cylinder, as the rings can easily be replaced.
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.