294 Diesel Technology Copyright Goodheart-Willcox Co., Inc. ❑ Some method of dissipating the kinetic energy of the waves as they enter the exhaust piping. The more effective the method of wave energy dissipa- tion, the lower the elevation difference required. A valve located where the exhaust piping penetrates the hull can keep waves from entering the exhaust piping when the engine is not running. The valve mechanism should not include any components which rely on sliding contact to maintain flexibility. This type of action has proven troublesome in an environment of saltwater and exhaust gas. A flexible strip of one of the chemically inert plastics can provide hinge action. In dry marine exhaust systems appropriate drain con- nections, rain caps, or other means must be provided to protect the engine from rainwater or sea spray entering the engine through the dry exhaust piping, Figure 13-26. Long runs of exhaust piping require traps to drain moisture. Traps should be installed at the lowest point of the line near the exhaust outlet to prevent rainwater from reaching the engine. Slope exhaust lines from the engine and silencer to the trap, so condensation will drain. Traps may be built by inserting a vertical pipe, with a drain petcock, down from a tee section in the line. The last few feet of the exhaust pipe discharge should be sloped to prevent rainwater or spray from entering the pipe. Alternatively, some form of rain cap should be fitted to a vertical exhaust pipe section. As with the wet exhaust system, a dry system’s exhaust pipe must be isolated from the engine with flexible connections. The dry mufflers and other large dry exhaust system components would be best mounted outside the engine compartment. Exhaust System Service Exhaust system components are subject to both phys- ical and chemical damage. Any physical damage to an exhaust system part that partially restricts or blocks the exhaust system usually results in a loss of power and poor fuel economy. In addition to improper engine operation, a blocked or restricted exhaust system causes increased vehicle noise and air pollution. Leaks in the exhaust system caused by either physical or chemical (corrosion) damage may result in illness, asphyxiation, or even death. Remember that vehicle exhaust fumes are very dangerous. Most exhaust system components, especially the exhaust pipe, muffler, DPF, DOC, and outlet pipe, are sub- ject to rusting and cracking. These parts are also suscep- tible to other types of damage, particularly on trucks. Clamps can break or work loose, permitting parts to sepa- rate. Components may fail due to the impact that occurs when the vehicle hits ruts and potholes in the road. Parts may also be damaged by rocks thrown up by the wheels. Warning: On all inspection and repair work, be sure to wear appropriate eye protection. Also, remember that exhaust system compo- nents get very hot. Before making a visual inspection, listen closely for any hissing or rumbling sound that may indicate the beginning of exhaust system failure. With the engine idling, slowly move along the entire system and listen for leaks. It is nor- mally not difficult to locate the source of a leak in this way. Expansion sleeve with spray shield Vertical pipe support Flexible pipe connection Flexible pipe connections Long sweep elbow Drain Slight pitch away from engine Pipe supports Pipe supports Engine exhaust outlet Long sweep elbow Figure 13-26. Marine dry exhaust systems also use water, but the gases do not make contact. (Caterpillar Trucking Co.)