It is not the intention of the author to describe indicators of the well-known Watt type. It is simply his purpose to call attention to the explosion-recorder which he has devised to supplement the data obtained by means of the indicator.
[Illustration: FIG. 145.--Mathot explosion-recorder.]
=Explosion-Recorder for Industrial Engines.=--The explosion-recorder illustrated in Fig. 145 can be adapted to any ordinary indicator. It is composed of a supporting bracket _B_ upon which a drum _T_ is mounted. This drum is rotated by a clock-train, the speed of which is controlled by means of a special compensating governor. The entire system is pivotally mounted upon the supporting screw _O_, so that the drum _T_, about which a band of paper is wound, may be swung against a stylus _C_, which records upon the paper the number and power of the explosions. These explosions are measured according to scale by a spring connected with an indicator. The records obtained disclose for any given cycle the amount of compression as well as the force of the explosion, and render it possible to study the phenomena of expansion, exhaust, and suction. They are, however, inadequate in showing exactly how an engine runs in general. Indeed, in most gas-engines, as well as oil and volatile hydrocarbon engines, each explosion differs from that which follows in character and in power; and it is absolutely essential to provide some means of avoiding these variations. The explosion-recorder gives a graphic record from which the number of explosions can be read, and also the initial pressure of each explosion, the number of corresponding revolutions, the order in which the explosions succeed one another, and consequently the regularity of certain phenomena caused by secondary influences, such as the section of the distributing members, the sensitiveness of the governor, and the like.
The explosion-records can be taken simultaneously with ordinary diagrams. In order to attain this end, the recorder is allowed to swing around the pivot _O_, so that the drum carrying the paper band is brought into engagement, or swung out of engagement with the stylus, as it is influenced by each explosion, thereby leaving its record on the paper. The ordinary diagram may be traced on the drum of the indicator, as it continues to operate in its usual way. Thus the explosion-recorder renders it possible to control the operation of engines, to obtain some idea of the cause of defects and to attribute them to the proper force. Improvements can then be made which will ensure a greater efficiency. A number of records herewith reproduced illustrate the defects in the controlling apparatus and in the construction of certain engines, and also the result of improvements which have been made on the basis of the records obtained. The smaller lines indicate the compression, which is usually constant in engines in which the "hit-and-miss" system of governing is employed, while the larger lines indicate the explosions. These records are only part of the complete data normally drawn on the paper in the period of 120 seconds corresponding with an entire revolution of the recorder-drum.