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Pressure Transient Distribution System (Firefighting Particularized)

pressure transient firefighting

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#1 Danielisimo


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Posted 13 September 2017 - 08:59 AM



I've been thinking about a physic problem a couple of days and I am stuck. I am going to particularized this problem to my case, but it can be applied to a lot of cases.


So, we have our firefighting ring with a shutoff pressure of 13barg. So, according to NFPA 20, my pressure set up is:


- Jockey stops at 13barg

- Jockey starts at 12.32barg

- Main Pump starts at 11.98 barg

- Diesel starts at 11.3 barg

(this is just for information)


The system is composed of: tank, pumps set, check valves, the pipeline and a valve at the end. 


If there is any leakage, I can suppose the system is over 12.32 barg (imagine no elevation), and the check valve and the valve at the end closed. If I open the valve, water starts flowing through the pipe, in this initial period, there is no pump running so the water release its energy, but air must go inside the pipe to occupy this "empty" room, and a pressure wave has to travel through the pipe to "inform" all system there is no obstacle to flow.


First of all: Am I wrong?

How Can I calculate the pressure drop of this pressure wave? Initial flowrate?

If there is no expansion tank, Could the pressure go down the main pump set up pressure directly, so the main pump starts and not the jockey?


Could someone define better what happens? I would like to understand well the phenomenum.


Thanks in advance.



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