EXHAUST PIPE AND PIT. WATER COOLING SYSTEMS Exhaust planning the installation of a low-pressure oil engine, the exhaust piping should be made as short and direct as possible. All elbows that are not absolutely necessary should be eliminated. In a horizontal engine plant the best pipe layout has the exhaust pipe running straight down from the engine to the exhaust elbow which rests in a pipe conduit. The exhaust pipe should run from the elbow, through the conduit, into the• exhaust pit, located outside the building. The pit should be at least 3 feet from the building wall to avoid fire risk. Good engineering specifies that the pipe conduit must have concrete walls and bottom and be provided with a cast-iron cover, al though a wooden cover will do in an emergency. The exhaust elbow should, if possible, be of special design with a clean-out door at the back; see Fig. 331. A tee instead of an elbow can be used with one outlet closed by a plug or blind flange. This ad mits of cleaning out the vertical pipe. Figure 332 shows a well planned pipe layout. If the conduit be extended along one side of the engine foundation, the oil and water piping can also be run in it, out of the way.
The majority of engine builders have the exhaust pipe sizes suitable for short lines only. If the building plan necessitates a longer run, the pipe should be increased at least one size. In laying the pipe, it should be sloped to drain away from the engine. A plugged opening should be drilled in each exhaust pipe immedi ately below the cylinder. By removing the plug, the operator can tell exactly how the engine is firing and the condition of the exhaust gases.
A common practice is the connection of two engines to a single exhaust pit. Each engine should have its individual exhaust pit or pot. With two-stroke-cycle engines, where a common exhaust pit is used, when only one engine is .in operation the exhaust gases will back up the second pipe and, if the piston is at the end of the stroke, enter the cylinder. If the exhaust is the least bit smoky, the unburnt carbon will settle on the cold cylin der walls in a gummy deposit. If much sulphur is in the fuel
oil, it will attack the cylinder of the idle engine.
Another installation error that is quite prevalent is the use of a water drip into the exhaust line. The water is used to cool the gases, thereby both deadening the noise of exhaust and lowering the back pressure. The water does perform its mission but has the objection of causing the exhaust to be wet. Because of this moisture a black, tarry deposit will settle over the entire surroundings. Increased pipe size and the use of a suitable pit will serve just as well without this objectionable feature.
Exhaust Pits.—Every low-compression oil engine, no matter where installed, should be provided with an exhaust pit. It is the practice of some manufacturers to furnish a cast-iron exhaust pot, which is located close to the engine. While this assists in dampening the noise of the exhaust, it does not, by any means, take the place of a pit.
Low-compression engines, regardless of make, when the in jection apparatus is not in the best of shape, display a tendency to allow part of the fuel charge to blow out through the exhaust ports while it is in a liquid condition. This is especially notice able when an oil having a heavy asphaltum base is used, because the cylinder temperature is not high enough to vaporize the heav ier portion of the oil. The same objection frequently is raised against heavy fuel oil when the engine is operating on low loads. On low loads the temperature of the bulb, or other hot ignition device, falls so low that it is unable to completely vaporize any of the fuel oils ordinarily used. As a consequence some of the oil, still unvaporized, passes out through the exhaust ports and enters the exhaust pipe. The same condition of unconsumed fuel en tering the exhaust pipe is often encountered when the governor or the injection nozzle fails to cut off the oil supply at the proper point.