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Gravity fed diesel line sizing

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HVACctrl

HVACctrl

Mechanical
Dec 13, 2002
332
Any rules of thumb on sizing a diesel line if used to feed diesel from a large tank to some diesel engines if gravity and fluid head (from the height of the fluid at the top of the tank) are the only things causing the flow?

 
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I have looked at some old threads on similar subjects. From what I am reading, my application is not really gravity fed in the sense that the pipe is sloped. In reality, the fluid head from the main tank is the only driving force.

 
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I would think you would want to have at least some minimal slope on the line, just to prevent dirt and grit accumulation, if nothing else, but as long as you have sufficient head, you'll get the flow you need. If you do not have a pump installed, one way or another, it is a "gravity feed" system.

Anything else?

 
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BidInch,
Is that virtual pipeline thing the way to size the pipe?

BTW, I belive the max gpm will be very low- say 4 to 12 gpm depending. I belive the fluid head will be no more than about 15 feet, probably less. I think the run will be less than 40 feet with maybe 4 to 5 90 deg elbows. None of this is certain becasue I haven't gotten that far yet.

 
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Virtualpipeline is my company information webspace page that I've just starting up on MSN. I think I'll be moving to a real website soon. There is not enough space there for what I would really like to do.

Let's say that's my business, sizing the pipe. I do piping system design, pipeline and pump station engineering, analysis and can even do complete operational simulations for an entire pipeline systems if needed. If you look hard enough there you might be able to find my e-mail address; remove the "nospam_" part from nospam_xxxx@xxxx.com or try leaving a comment somewhere and I'll get back to you personally.

I've already had a look at your url listing, but don't see much there except for a large black space and some listings towards the bottom. Nowhere to leave any info for you that I could figure out.

Depending on the flow, 15 feet might work OK, but it could also be marginal for a reasonable pipe diameter. Let me know when you've got some better info.



 
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Engineerboards was just started within the last two months as a spinoff from a site frequented by engineers regarding the PE test. Its a discussion board in its infancy. I am hoping that it gets more into other things aside from the PE test eventually.

Nice that you are running your own busininess.

My problem is probably seriously trivial for someone like you, but here it is.

Here is the latest and greatest:
-Diesel
-Liquid height will vary from 17.75 (tank full) feet down to 7.5 (tank empty) feet. Likely it will often be somewhere in the middle. In fact, It may never get to the max or the min listed here.
-Total pipeline from tank to engines is about 134' to the longest run.
-Total fittings: 8 ells, 1 full port ball valve, 1 emergency shutoff valve, 1 union and one SS expansion joint.

That's about it.

I also have to size a similar one with less flow and slightly different routing.

I'm mainly hoping someon can push me onto the right track to figure this out. I'll be glad to hear any feedback you may have.

Ed


 
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I think its gonna' be marginal. You only have 10 feet of head to work with with translates to a diesel pressure of about 4-5 psi total. It will flow, but not too much. Your flow demand is critical at this point. How much engine do you have on the end? Do you know the maximum rate of fuel consumption or do you have an idea of how much horsepower you will have runnng?

In the meantime I'll try to find a nice diagram of fuel day tank systems I have filed away somewhere.

 
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Thanks for the help.
Engines appear to operate on 0.62 gpm max. There is a holding tank at each engine. There is also a pump at each engine. However, the pump will often be bypassed and not used. The pumps are capable of 2gpm. 2gpm x 6 is where I got my 12 gpm requirement.

I didn't consider the suction of the pump to help drive the diesel.

I suppose I could throw that in or reduce the flow to 0.62 times 6.

The head will be 7.5 at a min and 17.75 at a max.

Ed

 
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HVAC,

Here you go, just as you originally asked for, "rules of thumb for fuel oil handling system design"

"RULES OF THUMB
As a rule of thumb for sizing generator fuel oil systems, each 100kw of generator capacity will consume about 7 gallons per hour. Any oil that is pumped to the engine but is not returned to the day tank would add to the generator capacity based requirement."

Popped that off of a *.pdf doc with a bunch of info you'll like. You can get the whole thing at,


Just let me know if you think of something else.

 
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hvacctrl,

to supplement previous postings . . .
you need to determine & ensure that the pump inlet conditions at gen set are met or exceeded OR the mfg recommended pressures at point of connection for gen set are met.

good luck!
-pmover
 
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pmover,
Gotcha!
Only thing is that the pump at the engine was originally not in the design. It really isn't needed due to gravity flow, but we can use it as a backup since its already there. There will be two parallel supplies to the day tank- one through the pump and one fed by gravity alone.

In general, I'm not thinking about the pump since I THINK (not sure) that whatever we design for by gravity feed alone should be good enough for when the pump is running.

Ed


 
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Ed, looks to me like you should be able to get your 12 gpm plus some out of a 2.375 OD, without resorting to using the pump. Use the thinnest pipe wall thickness you can get your hands on. I don't recommend lower than that OD, unless you want to run the pump sometimes.

 
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Its the Churchill equation.
Direct solution for head/press loss.
NO friction factor iteration!
Works for laminar or turbulent flow, any diameter, any liquid.

Click on the virtualpipeline link, below,
Click the profile tab,
Scroll to the bottom,
see "Work e-mail"

Here's the hard part; delete "nospam_"

then, just send me something interesting.

I'll reply with the XL spreadsheet attached.


 
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Sounds like a great deal! I'll have to find something worhty to send you. Let me look around to see what I have.

Seriously, thank you very much for the help!

BTW, I finally got ahold of the engineer who designed the first part of this and sent him some questions about his assumptions, etc... when he made the calcs. He told me, "we didn't get that sophisticated. We just used a huge manifold pipe, etc..."

I guess I might be over-analyzing! But, hey, that's me sometimes! :)

Ed

 
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