Piston

—A device for receiving the pre ure of, or operating upon, a fluid in a cylinder or tube. It usually consists of a short cylinder, fitting within a cylindrical ve el, along which it moves back and forth. It is used in steam engines to receive motion from the steam, and in pumps to transmit motion to a fluid. It is the e ential part of a reciprocating engine; a metal disc working in the cylinder, under the pre ure of steam, and connected means of a linkage of rods with the cranked rotating shaft, whereby the power is_ usefully applied. In locomotives, the piston is either solid, with Rams bottom or snap rings fitted into grooves in its circumference,or else is built up with metallic packing rings, retained in place by a plate or ting. In such cases, the body of the piston is termed the head, any solid ring used to separate the split packing rings is the bull ring, while the retaining plate or ring is known as the follower.