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Member

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Estimating Static Head in Mutiple Discharge Points

11/01/2011 4:03 AM

In estimating the head loss in a firewater pipe network taking water to the top of a number of petroleum products storage tanks, the frictional loss of each line can be easily estimated using the Hazen-Williams formular.

However on the side is the static head represented by the height of the liquid surface above the pump impeller eye. With multiple tanks, would you also calculate the static head of each line or would the height of the highest tank be sufficient as an overall static head.

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Associate

Join Date: Jul 2010
Posts: 31
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#1

Re: Estimating Static Head in Mutiple Discharge Points

11/01/2011 7:55 AM

As pump capacity is both - the head as well as flow, therefore, in this case maximum height should be our static head to which friction head of each of the branch lines shall be added to get the total discharge head.

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Guru

Join Date: Apr 2009
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#2

Re: Estimating Static Head in Mutiple Discharge Points

11/01/2011 11:05 PM

Each line is calculated separately. Using Hazens and Williams formula calculate all offshoots as separate calculations, ignoring parallel or tee branches in terms of frictional losses.

My recommendation...use subsurface foam injection. MUCH more effective in the case of a storage tank fire. And guess what happens when a tank fire occurs...everyone runs the other way...employees do not fight fires...automatic systems do.

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#3

Re: Estimating Static Head in Mutiple Discharge Points

11/01/2011 11:05 PM

1. Only one static head - use the highest tank static head as the basis of design

2. Pump capacity shall be the total flow of each branch

3. For the pressure drop, use the longest route as the basis and the flow rate for that route

4. Total head = static head (highest tank) + frictional head loss for one branch (longest route)

5. Assuming symmetrical piping, same line size and same flow rate for each branch

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#4

Re: Estimating Static Head in Mutiple Discharge Points

11/02/2011 4:09 AM

Thanks Sabriahmad, from your comment

4. Total head = static head (highest tank) + frictional head loss for one branch (longest route)

Will account for frictional head of the longest route only account for frictional head loses in multiple tanks in a worst case scenario where you need to send water and foam through separate pipes to a burning tank and you need to sprinkle water on 5 or 6 adjacent tanks?

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Commentator

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#5
In reply to #4

Re: Estimating Static Head in Mutiple Discharge Points

11/03/2011 7:53 PM

1. The tank on fire will require foam to extinguish the fire.

2. Adjacent tanks require water to cool the tank down

3. Thus, the worst case scenario would depend on the tanks farm layout. You may have two or more adjacent tanks on consideration.

4. Ensure that the total flow is the one required by all tanks, Not just individual tank.

5. Individual tank consideration is only for pump head requirement. Capacity is based on total water requirement (at least tank on fire plus adjacent tanks fire water requirement)

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sabriahmad (2); VishalB (1); WJMFIRE (1); Yinka Akinkunmi (1)

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