N40475 Chapter 7 Typical fuel systems The more simple the fuel system, the better it will perform in service. Figure 1 shows an ideal system. 1. Fuel tank. 2. Fuel return pipe. 3. Manual fuel feed. 4. Stop cock. Figure 1 5. Vent. 6. Drain. In some applications there may be legislation that requires that fuel lines draw from, and return to , the top of the tank. Figure 2 shows an acceptable arrangement. 1. Fuel tank. 2. Fuel return pipe. 3. Manual fuel feed. 4. Vent. 5. Fuel feed tap. 6. Drain tap Figure 2 The fuel tank may be steel, aluminium, or G.R.P. or, alternatively, a rubber bag tank may be used.
The main fuel connection is taken from the rear of the tank so that all the fuel is available for use when under way when the hull will be at an angle. The fuel return is extended within the tank to near the bottom in order to prevent air locks which can arise due to siphoning of the fuel when the engines are stopped. The fuel lines may be of metal, either copper or ‘bundy’ steel tubing used either with compression fittings or preferably soldered nipples, with a flexible armoured rubber hose to connect to the primary fuel filter.
This simple fuel system is satisfactory when one or more engines are run from a single fuel tank, and it may also be used when there are two tanks each supplying one engine. In the latter case the system may include a cross connection, between the tanks by means of a balancing pipe, with a valve, at each end.
In some installations cross connecting pipes between the two engine feed pipes and the two engine return pipes have been used, but valves are necessary in every line so that the appropriate system may be selected, and the complexity of installation and operation is such that the advantages in operating flexibility are out-weighed by the possibility of obscure problems due to component malfunctions, incorrect operation or engine interaction. Page 21