Kohler 20--2800 kW Transfer Tanks, Diesel Fuel System with Overhead Main Tank and Transfer Tank

Flexible connections must be used wherever there may be relative motion between piping and supplied equipment. Always use flexible lines at the engine connections. These should be a minimum of six inches (15.3 cm) long.

Diesel engines require at least two fuel lines: one supply and at least one return from the fuel injectors. More fuel is delivered to the injectors than the engine will use and the excess must be returned to a transfer tank or the main storage tank. Fuel return lines should be at least the size of the supply lines. They should be unrestricted, as short as possible, and allow gravity return of fuel to the storage tanks.

In some installations it may be difficult or inconvenient to route return lines so that fuel will flow by gravity. Before designing a system which will have any head of fuel on the return lines, the details should be approved by the engine supplier. Serious problems with engine hydraulic lock or uncontrollable overspeeding will result from any return fuel line restriction on some diesel fuel systems.

6.4 Transfer Tanks

The term “transfer tank” and “day tank” are often used interchangeably. Both are used to ensure engine starting in the minimum possible time after a power failure by means of a quantity of fuel stored in a tank adjacent to the engine. This allows the engine fuel transfer pump to easily draw fuel when starting and provides a convenient location to connect injector return lines. Standard tanks are available in sizes from 5-275 gallons (19-1040 L) with or without integral electric fuel transfer pumps. They can also be provided with fuel level gauges, manual priming pumps, float switches for pump control, float valves, rupture basins and low level alarms. A float switch controlled solenoid anti-siphon valve or a float valve should be used whenever there is a possibility of siphoning fuel from the main storage tank, or when the fuel level in the main tank may be above the level of the transfer tank inlet. Engines are subject to derating for fuel temperature above 100°F and are subject to damage if operated with fuel temperature above 140°F. A day tank sized for two hours fuel consumption should prevent excessive fuel heating by fuel returned from the engine. If smaller day tanks are used, the engine supplier may recommend routing engine fuel return lines to the main storage, or installation of a fuel cooler. See Figure 6-3.

						4
			1	2		3
						5
						6
	10	9	8		7
1.	Vent				6.	Fuel shutoff solenoid
2.	Return line				7.	Transfer tank
3.	Main supply line				8.	Filter
4.	Overhead main tank				9.	Flexible line
5.	Maximum 25 ft. (762 cm), minimum 1 in. (31 cm)				10.	Fuel pump

Figure 6-3 Diesel Fuel System with Overhead Main Tank and Transfer Tank

TP-5700 7/93 Section 6 Fuel Systems 27