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Diesel Fuel Return Line

Diesel Fuel Return Line

Diesel Fuel Return Line

I am writing on behalf of The Philadelphia Ship Preservation Guild, the Guild, which is a non-profit organization of which I am a member. The Guild is the owner and operator of two historic ships: a tug boat and tall ship. Additional information can be found at the website www.gazela.org.
As the Guild’s name implies, restoration of historic ships is the main focus of the organization. Volunteers of men and women comprises the Guild who devote an enormous amount of man-hours in the 2-½ year complete restoration effort which is approaching the end of the first year.
I am trying to determine the size (dia.) of the piping, fittings and valves, to use for a diesel fuel Return line back to the fuel tanks from the main propulsion engine and the two diesel-driven generator sets. I am of the electronics background and just learning diesel engines and fuel lines. Since I'm a volunteer for the Guild, I volunteered to do design and install the fuel return lines. Presently, the return fuel is fed back to the dual fuel filters, not the three 1,200 gal. fuel tanks. The fuel should be fed directly back to the fuel tanks, not the filters.
Knowing the gallons per hour of the unburned fuel from each of the three engines, I need to know what formula is used to calculate the size of pipes I need to return the fuel from each engine back to the fuel tanks. For example, the two generator sets will return approx. 10.5 G.P.H (a total of 21 gph), and the propulsion engine will return approx. 9 gph for grand total of 30 gph. The runs of each piping system from each engine to the fuel tanks will be approx. 25 feet. How do I figure the diameter of pipe?

Thank you,
George Kerlyn

RE: Diesel Fuel Return Line


To size the pipes, you need to know (or specify) the velocity at which the fuel will flow through the pipes.  I can't help you with that... but when you know it, you can use the following equation:

Q = AV  Where:

Q = volumetric flow rate (gpm)
A = Pipe cross sectional area (PI/4*D^2)
D = Pipe diameter
V = Fluid velocity

Solve for the pipe diameter. (be sure to watch those units!)

Good Luck!


RE: Diesel Fuel Return Line

Thank you very much "jproj".  I'll try to find out what the fluid velocity might be.  Didn't know I needed this because I didn't know what the equation was until now.

See, I'm from the electronics background, but offered to work on this piping project without any prior knowledge or experience.  Therefore, I appreciate your help.  Slowly, but surely I'll be learning fluid dynamics I suppose.


RE: Diesel Fuel Return Line

marinerTwo - If you or any of the others working on the old ships would like to get a better handle on this kind of technology, check out engineering books on e-bay. There's a steady stream of old Audels books on marine engineering, diesel engines, etc. I've got an old set of Audels Plumbers & Steam Fitters books, and they've got a section specifically on marine piping. Good luck with your project - it sounds like fun!

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