THE INTERPRETATION OF INDICATOR DIAGRAMS. By CHARLES I. CORP, Lawrence. THE important and essential' knowledge to be derived from a careful investigation and study of indicator diagrams is invaluable to the engineer, as they enable him easily to ascertain and establish various facts concerning the use of steam that by any other method would prove complicated and unsatisfactory, of which the following may be stated: First. It shows whether the valves of an engine are correctly and evenly timed, and also serves as a guide in all necessary adjustments of the same that may be required, in order to insure the best distribution of the steam working within the cylinder, and thereby securing the maximum economy and efficiency of the engine. Second. The indicator power developed in the cylinder of an engine may be determined; also the quantity of energy lost in various ways; such as leakage of valves, back pressure, too early release, and incorrect adjustment of valves. Third. It indicates whether the steam-ports and passages are adequate in size, and a diagram taken from the steam-chest will also show whether the steam-pipe and its connections are of sufficient size. Fourth. It indicates the condition of the valves and piston in reference to the leakage. Fifth. In connection with a feed-water test (showing the actual amount of steam consumed), the economy with which the engine works may be determined. To ascertain with accuracy each and every item of information mentioned above, it is absolutely essential that the diagram should truly represent the position of the piston, and also the pressure exerted on both sides of it, at every point of its stroke. The general features of a diagram that indicate a proper distribution of the steam in an engine cylinder is represented by diagram, the attainment of which (as near as possible) should be the endeavor of an engineer in setting the valves of his engine. AA is the atmospheric line and BB represents the boiler pressure. B B A A In this diagram the initial steam pressnre, which is the highest pressure realized in the cylinder, is fully maintained up to the commencement of cut-off; indicating ample size of steam-pipes, ports and other passages in the engine. The expansion curve is good, and the release of the steam is sufficiently early to secure a free exhaust, also low and uniform back pressure. The exhaust valve closes on the return stroke, in time to provide the necessary compression (or cushion), and thereby counteracting in part the effects of inertia and momentum of the piston, crosshead, and other reciprocating parts, at the end of the stroke. The admission of steam takes place promptly, and projects the admission line to initial pressure at right angles (or perpendicular) to the atmosphere line. These qualities in a diagram are an especial requisite under any circumstances, to insure an economical working engine. In practice, however, there will be a great difference in the outline and appearance of the cards from the different engines, and even from the same engine, arising from numerous circumstances and conditions connected with it. The diagram, as before stated, simply shows the pressure of steam existing in the cylinder at each part of the revolution of the engine, and it is the province of the engineer to determine whether these pressures at each and every point are the correct ones, and, if such is not the case, to ascertain wherein the fault lies that causes the error; then determine upon and apply the remedy. It must be understood that, in a great majority of cases, the |