Flow of fluid from one tank to another under gravity

[P.101]

Hello all, I am new to this page and also new to a slight change my career has had. I am installing fuel tanks and have seen on many previous sites tanks that are in buildings around 5-6m up and supplied by a larger bulk tank at ground level. The bulk tank has an inline fuel pump and supplies the smaller raised tank as and when fuel is required( controlled by level gauge) the supply pipe is 1inch, there is also a second pipe 1.5 inch which is connected at the highest point on the smaller raised tank and this then returns along the floor down the external building wall along the floor then up the side and into the top of the bulk tank. This is acting as and over fill prevention of the smaller raised tank i believe. There is also a breather on the smaller raised tank which is raised around 4 feet off the tank, now to my question.

Will the liquid flow out of the tank through the 1.5 inch over fill pipe along the floor in the machine room, down the external building wall along the floor, up the side of the bulk tank at ground level and in. I wasn’t sure if gravity would push the fuel along the floor and back up into the tank, the bulk tank is around 2M heigh.

I appreciate that is a lot to read, any clarification on what I’m trying to get across please ask. And I will draw a photo of the system.

Any help much appreciated

 

[1503-44]

I'll try to explain a little bit, while in the meantime you draw us a picture and measure the elevations of inlets and outlets.

It sounds like it will move from tank to tank, but of course only if the elevations of inlet and outlets are properly set within the laws of physics which allow that kind of thing to happen. First, draw a straight line between outlet on one tank to the inlet of the other. If all the pipe inbetween them is under that line, you have a chance of making it work.

The second problem might be how fast you might want that overflow line to flow. It should at least flow as fast as the pump can fill the higher tank, or there will be some risk of overflow, right. Unfortunately the overflow line being only powered by gravity is not likely to have such a high flow capacity as your pumped inflow line.

All the rest we could tell you about this depends on how well you do your sketch of the system. Elevations, pipe diameters and lengths of pipes, and their slopes, if any, will all be important things to know. Dont forget to check the flow and pressure rating of the pump.



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I take no responsibility for any damages or injuries of any kind that may result.

 

[bimr]

When transferring fuel, it is generally good practice to have some type of automatic overfill protection.

There is also a issue with combustible liquids in buildings. One or more fuel oil storage tanks containing Class II or III combustible liquid shall be permitted in a building. The aggregate capacity of all tanks shall not exceed the following: 660 gallons (2498 L) in unsprinklered buildings, where stored in a tank complying with UL 80, UL 142 or UL 2085.

 

[LittleInch]

The overflow needs to be sized to accommodate the max flow from the pump on the big tank. The driving force on the overflow is limited to the height between the overflow and the exit into the big tank.

It does not really matter that the pipe goes down then back up but the longer the pipe and the greater the number of fittings and elbows the lower the flow rate.

However, the bigger pipe makes a lot of difference. Personally I would have gone for a 2" overflow to be really sure but the flow from the pump might be quite small.

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Also: If you get a response it's polite to respond to it.

 

[bukol]

Since the return operates by gravity you need to fill all the pipes. You need to put a drawing of the installation. Any comment I make on this without the drawing I consider hearsay. I mean I can not help you.

 

[LittleInch]

That's a good point. If the overflow has a low point then once it works the fluid will stay there but there will be air in the pipework higher than the tank entry point. As the overflow starts to work it will initially be open channel flow like a roof drain pipe, before gradually transitioning to a full pipe scenario.

This is sometimes difficult and you get air bubbles and increased flow resistance during the transition from partly full pipe to full pipe.

If it goes wrong you can get air locks and air trapped in the overflow line.

A continuous fall of the pipe from overflow to the return tank is a lot better to avoid these issues.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bukol]

"before gradually transitioning to a full pipe scenario."
Not if the arrangement of the pipe is such that it traps air in. If overfill happens and there is trap air, water hammering can occur. very nasty for piping system. You need to make sure that air can escape once overfill happened. But unless there is a drawing I can not tell you what is correct or wrong.

 

[1503-44]

Can we wait for the sketch.
We know nothing about anything, except one tank is higher than the other. So far, its possible.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

 

[bukol]

"Can we wait for the sketch."
Thats what I have been saying for the only two post I made on this thread. "We need the skecth" Now someone is telling me to wait for it after he promptly tried to explain what is happening

 

[1503-44]

Bukol, my last and only post was the first one way up at the top. There I said nobody was going to tell him anything more useful than what I had already told him without a sketch and sure enough, that is true. Please have a seat and try to be a little patient. Thank you.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

 

[P.101]

Thank you for your comments I really appreciate the replies. I will generate a sketch for you all this weekend, apologies in the delay.

Thanks

P

 

[1503-44]

Just don't ask for it by Monday morning.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

 

[P.101]

Hello apologies for the delay, please see a sketch attached. It should illustrate the total pipe length and the total fall etc.

Can someone please advise me on the formulas to work out the gravitational flow of diesel through pipe work. I have found info relating to the Hazen-Williams equation but it says it only relates to water.

Again any advise would be much appreciated

P

 

[LittleInch]

That bottom U bend is a really bad idea.

The problem you have is that at rest, that will be full of water, or assume it will be if the overflow has ever been in use.

Then your top tank starts to overflow. To start with there will be water not filling the pipe so you don't flush out the air in those vertical legs. The air is trying to go in the opposite direction to the water as the pipe fills. This is difficult and can cause extra flow resistance and maybe even prevent flow in the pipe and all the time your overflow isn't working and the level in the tank is going up.

You really want to have your overflow on a continuous fall all the way into the top of the bottom tank.

If your top tank has a lot of free board over the overflow it might work, but there will be a risk it won't.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[P.101]

Hello thanks for your response, this had been something I wondered.

Can I ask what you mean by free board?

And do you know the calculations and formula for working out the flow rate of diesel fuel through pipe work under gravity?

Thanks

P

 

[LittleInch]

Free board in this case is the max height of the liquid above the level of the overflow before it spills out of the tank.

The problem you have in calculating flow is that it starts as an open pipe/channel flow and transitions, maybe, to full pipe flow. That transition is very difficult to calculate as a calculation as opposed to transient analysis.

Open pipe flow is mannings equation and an element of riser flow for the vertical sections.

All too complex for me.

I would just put in a 2" or 3" or 4" pipe at a gentle slope back to the main tank...

Basically that overflow line is a bad job and could easily not carry the max flow it needs to.

Sometimes you just need to go with big and forget trying to calculate things...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

Hello thanks for your response, this had been something I wondered.

Can I ask what you mean by free board?

And do you know the calculations and formula for working out the flow rate of diesel fuel through pipe work under gravity?

Thanks

P

"When transferring fuel, it is generally good practice to have some type of automatic overfill protection.

There is also a issue with combustible liquids in buildings. One or more fuel oil storage tanks containing Class II or III combustible liquid shall be permitted in a building. The aggregate capacity of all tanks shall not exceed the following: 660 gallons (2498 L) in unsprinklered buildings, where stored in a tank complying with UL 80, UL 142 or UL 2085."

Your first step should be to discuss this project with someone that is familiar with the local fire code as it would appear that you are likely violating the building code with so much combustible fuel inside of a building.

 

[pierreick]

Hi,
Consider the document attached to support your work.
Good luck
Pierre