The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

Peyn MARINE REVIEW. ~ 14 mee The Indicator Diagram. The chief function of the indicator or steam pressure re- corder, is to graphically represent the pressure in the cylinder of a steam engine at any or all points in the stroke of its piston. That it must do so is evident, from the fact that the diagram it produces is the compound result of two concurrent movemements --that of the paper drum in coincident with that of the piston of the engine; and that of the pencil in obedience and in propor- tion to the pressure acting on the piston. Referring to the illustration, on the left and about midway in the height of the card is a point marked '"'lead opening." At this point the valve begins to open the steam port at that end of the cylinder at which the card is taken. This occurs a little be- fore the piston reaches the end of the stroke and the crank reaches its position at the dead center, so that when the piston reaches the end of the stroke and the crank is on the dead cen- ter, the valve will have opened the steam port for ashort dis- tance. 'The nearly vertical line above the point marked "lead opening" is called the "admission line" and during the period in which the pencil of the indicator draws the line, the steam from the boiler is admitted to the clearance space, raising the pressure, Steam line --_ <= Cut off Sto, id 7 ™m Peng Admission line > Leal opeaing St e > Nay Uy, Py Ch, 05 &. 9, Sto, - 42), an Back pressure or exhaust line is higher at the point of steam opening, it shows a very late opening of the steam port, a condition which does not often oc- cur in actual practice. At the point of cut-off marked on the card, the steam port is closed and further admission of steam from the boiler to the cylinder is prevented. The distance be- tween the initial end of the diagram and the point of cut-off, compared with the entire length of the card, shows the propor- tion of the stroke during which steam is admitted, and according to this proportion the point of cut-off is said to be at1/5 1/4 1/3 etc., stroke. 'The point of cut-off is rarely exactly shown by the diagram. Generally the steam line and expansion line are connected by a curved line, more or less irregular. This is shown in the diagram by the short portion of the line immediately following the point of cut-off; where the curve is the reverse of the expansion line. The line between the point of cut-off and the point of exhaust opening is called the 'expansion line" and as its name indicates, it shows the fall of pressure during the period when the steam is expanding in the cylinder. 'This line is fre- quently wavy, caused by the vibration of the arm carrying the' indicator pencil and the oscillation of the spring above the indi- cator piston. A wavy expansion line should not, however, be taken as indicating corresponding variation in pressure in the Inghaust gpening f- and consequently the pencil of the indicator to a point which in- dicates a greater or less approach to boiler pressure, depending on the construction of the valve, amount of lead opening, and length and size of pipe between the valve chest and boiler. "Ihe admission line should be nearly vertical. If with a fine pointed pencil, a line is drawn perpendicular to the atmospheric line and just touching the corner of the diagram at the point marked "'steam opening," and the admission line inclines away from the perpendicular instead of toward it, it shows that the full initial pressure is not realized until after the piston has started on its forward stroke. At the point marked "steam opening,' the steam valve or the steam port is, or should be, opened so rapidly that the full initial pressure will be maintained throughout that. portion of the stroke before the point of cut-off. Whether this is so or not is shown by the steam line between the point of steam opening and point of cut-off. If this is parallel to the "at- mospheric line,' it shows that the valve opens quick enough and wide enough to admit steam from the boiler sufficient to keep up the pressure notwithstanding the forward motion of the piston. If it drops toward the point of cut-off, it indicates that the valve does not open wide enough or quick enough and that the pipe between boiler and engine is not of sufficient size. If, on the other hand, it inclines upward to the point of cut-off, or _ engine cylinder, the true line being an average between the ex- tremes of the undulations. The expansion line should chiefly be studied to determine whether any leaks exist in the valves or by the piston, and to this end it is necessary to plot on the card the "theoretical curve." ; At the point marked "exhaust opening," the valve begins to open the exhaust port. A well designed valve will generally bring this point of exhaust opening very near the end of the stroke and the valve will open quick enough and wide enough - to cause the pressure to drop to the back pressure or exhaust line by the time the piston begins the return stroke. The line between the points marked "exhaust opening" and "exhaust closure" isthe back pressure or exhaust line- and shows the pressure against the piston in opposition to that on the other side, which forces it forward. - The nearer this line approaches to the atmospheric line, the less the back pressure. At the point marked "exhaust closure," the valve closes the exhaust port and the steam remaining in the cylinder is compressed and its pres- sure raised in proportion to the amount of compression. The line traced during the period when the compression takes place is called the 'compression line" and it terminates when the lead opening begins. The atmospheric line, which should be traced on every card taken, is the straight line at bottom.--Exchange. UTOMATIG = - [TIGHTING INCANDESCENT PLANTS OF OUR MANUFACTURE are endorsed by the following Qwners and Managers of some of the Finest Steam Yessels on the [;akes: IF YOU WANT your Steamer equipped with an....... AUTOMATIC INCANDESCENT LICHTING PLANT, Which can be handled by an engineer without any previous knowledge of electric plants, and which will operate arc and incandescent lamps from the same dynamo, write the Fisher [¢lectric (Jompany, . )etroit, Mich. ©