Q. How much of this evaporation was due to the superheater? A. An average of 23.7 per cent of the equivalent per square foot of heating surface. Q. Give an example from recent good practise of the thermal efficiency of a locomotive at various horsepowers. A. The following is from Penna. R. R. tests of a K 4 s heavy passenger engine: Q. Show the effects of superheating on the water consumption under stated conditions of recent good practise. A. Taking the K 4 s engine of the Penna. R. R., we have the following official figures: CHAPTER XLI FEED WATER HEATING Q. What is the object of heating the feed water? A. To reduce the work demanded of the fuel on the grate, by utilizing some of that in the combustion gases that would otherwise escape from the stack at a high temperature; also to lessen the injurious effect of injecting cold water into a hot boiler; and to steady the evaporation. Q. How much saving can be effected by heating the feed? A. In theory, as expressed in the annexed table. In practise, less. For other temperatures and pressures in the same way; that is, increasing with the initial feed temperature and decreasing with the gage pressure. Q. Describe the Elesco feed-water heater. A. Forward on the engine, in front of the cylinders and under the boiler overhang, is a horizontal tank, fed from the tender by a steam pump and piped to the usual boiler check valve; also receiving about 10 to 15 per cent of the exhaust steam. It contains quadruple groups of small tubes 4 feet long, so coupled as to give the feed 16 feet travel in each group. Through these the cold water from the tender passes, surrounded by the hot exhaust. The condensed exhaust, having given up most of its heat to the feed, is discharged through a filter (to remove the lubricating oil) to the tender tank. Q. Does not the heater increase the back pressure? A. No; it decreases it slightly, by acting as a condenser. Q. Where is the filter placed? A. On top of the tender, back of the coal space. Q. How is the water raised to the filter level? A. Ordinarily there is enough pressure in the heater to do this; but when there is less this is done by means of an auxiliary tank having a float operating a small valve controlling air pressure from the main air reservoir. The discharges from this valve and from the tank are connected with the heater shell; so that when there is back pressure the water will be forced to the filter; but where there is none, the auxiliary tank fills, the float rises, the opening from the heater is closed, and air is admitted to the tank, forcing the condense through the filter to the tender tank. Q. How is the pump to the heater controlled? A. By a steam valve so placed that the engine-runner can reach it even when his head is out of the cab window. Q. What prevents the cold-water line from freezing when the engine is standing? A. A small steam line directly from the boiler. Q. What rise in feed temperature is effected? Q. Does not the device lessen the draft? A. Yes; but less air is needed, as less coal is burned, due to the increased feed temperature. Q. About how much of the heat in the coal is utilized in the cylinders? A. About seven per cent only. Q. Give an idea of where the rest goes-say with an engine using $900 worth of coal a month. A. It has been estimated that the distribution, expressed in money and percentages, is about as follows: |