Diesel Fuel Supply

MECHANICAL INSTALLATION — FUEL SYSTEM (DIESEL)

Consider the following when installing a diesel fuel supply system:

Fuel supply tank construction, location, installation, venting, piping, testing, and inspection must comply with all applicable codes. In addition, see NFPA Standards No. 30 and No. 37.

Fuel supply tanks must be adequately vented to prevent pressurization, have provisions for manually draining or pumping out water and sediment, and have at least a five percent expansion space to prevent fuel spillage when the fuel heats up and expands.

The fuel lift pump, day tank transfer pump, or float valve seat should be protected from fuel supply tank debris by a pre-filter or sediment bowl with a 100 to 120 mesh element.

The supply tank must hold enough fuel to run the genset for the prescribed number of hours (NFPA No. 110 Class designation) without refueling. Tank sizing calculation should be based on the hourly fuel consumption rates on the genset specification sheet.

For emergency power systems, codes might not permit the fuel supply to be used for any other purpose, or may specify a drawdown level for other equipment that guarantees the fuel supply for emergency power use.

The cetane rating of No. 2 heating oil is not high enough for dependable starting of diesel engines in extreme cold weather climates. Therefore, separate supply fuel tanks for emergency power and building heating systems may have to be provided.

Approved flexible fuel hose must be used for connections at the engine to prevent damage from genset movement and vibration.

Diesel fuel lines should be black iron pipe. Cast iron and aluminum pipe and fittings must NOT be used because they are porous and can leak.

Galvanized fuel lines, fittings, and tanks SHOULD NOT be used because the galvanized coating reacts with the sulfuric acid that forms when the sulfur in the fuel combines with tank condensation. Such a practice would result in debris that can clog fuel pumps and filters.

Although copper has been used for diesel fuel lines in the past, black iron pipe is preferred. Diesel fuel polymerizes (thickens) in copper tubing during long periods of standby. This can cause the fuel injectors to clog.

Refer to the engine specification sheet for the maximum fuel inlet and return restrictions, the maximum fuel flow, and the fuel consumption. Then refer to Table 10 for the minimum hose and pipe sizes for connections to a supply tank or day tank that is relatively close to the set at approximately the same elevation. Hose and pipe size should be based on the maximum fuel flow rather than the fuel consumption (The maximum fuel flow can be twice the full-load fuel consumption). It is highly recommended that the fuel inlet and return restrictions be checked before the set is placed into service.

Separate fuel return lines to the day tank or supply tank must be provided for each generator set in a multiple-set installation to prevent the return lines of any idle set from being pressurized. Also, a fuel return line must NOT include a shut-off device. Engine damage will occur if the engine is run when the fuel line is shut off.

A day tank is required whenever pipe friction and/or supply tank elevation, either below the fuel pump inlet or above the fuel injectors, would cause an excessive fuel inlet or return restriction.

For critical start applications, where gensets are paralleled or must satisfy emergency start-time requirements, it is recommended that a fuel tank or reservoir be located such that the lowest possible fuel level is not less than 6 inches (150 mm) above the fuel pump inlet. This will prevent air from accumulating in the fuel line while the genset is in standby, eliminating the period during start- up when the air has to be purged.

Table 10. Minimum Fuel Supply / Return Hose and Pipe Sizes

		Fuel Supply Line				Fuel Return Line
Maximum	0-10 Feet		10-50 Feet		0-10 Feet		10-50 Feet
	(0-3 Metres)		(3-15 Metres)		(0-3 Metres)		(3-15 Metres)
GPH
Fuel Flow	Flex	Pipe I.D.	Flex	Pipe I.D.	Flex	Pipe I.D.	Flex	Pipe I.D.
	Hose	Inches	Hose	Inches	Hose	Inches	Hose	Inches
	Size	(mm)	Size	(mm)	Size	(mm)	Size	(mm)
0-15	No. 6	5/16	No. 8	13/32	No. 4	3/16	No. 6	5/16
		(7.9)		(10.3)		(4.8)		(7.9)

16-20	No. 8	13/32	No. 10	1/2	No. 4	3/16	No. 6	5/16
		(10.3)		(12.7)		(4.8)		(7.9)

21-80	No. 10	1/2	No. 12	5/8	No. 8	13/32	No. 10	1/2
		(12.7)		(15.9)		(10.3)		(12.7)

81-100	No. 12	5/8	No. 16	7/8	No. 8	13/32	No. 10	1/2
		(15.9)		(22.3)		(10.3)		(12.7)

101-160	No. 16	7/8	No. 16	7/8	No. 10	1/2	No. 12	5/8
		(22.3)		(22.3)		(12.7)		(15.9)

160<	No. 16	7/8	No. 16	7/8	No. 12	5/8	No. 12	5/8
		(22.3)		(22.3)		(15.9)		(15.9)

Based on four straight fittings, two 90° fittings, and minimal fuel lift height

INDUSTRIAL GENERATOR SETS — APPLICATION & INSTALLATION MANUAL — REV. #4 (09/07/07) — PAGE 39