N38143 Chapter 3 In some applications there may be legislation that requires that fuel lines draw from, and return to, the top of the tank. Figure (B) shows an acceptable arrangement. The fuel tank may be steel, aluminium, or G.R.P. (Glass Reinforced Plastic) or, alternatively, a rubber bag tank may be used. The main fuel connection is taken from the rear of the tank (B1) so that all the fuel is available for use when under way when the hull will be at an angle.
The fuel return (B4) is extended within the tank to near the bottom in order to prevent air locks which can arise due to syphoning of the fuel when the engines are stopped The fuel returned to the tank should be kept away from the main fuel feed, to avoid recirculation. A drain tube (B5) should be fitted to aid servicing and cleaning. From the tank the main engine feed line (B2) goes first to a water separator (B3), preferably one fitted with a thick clear plastic bottom and a drain cock (use only if allowed by local regulations).
The fuel lines may be of metal, either copper or seamless steel tubing used either with compression fittings or preferably soldered nipples, with a flexible armoured rubber hose to connect to the fuel lift pump. Stop cocks (B6) may also be fitted where necessary. 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 13