Calculate the location for a break tank
Calculate the location for a break tank
(OP)
Hi All,
I have what should be a simple problem but I can't get my head around it.
I have a high level tank at elevation approx 1600m. A 350mm pipe runs down the valley to a low point of approx 600m and up to another tank on the other side at approx 800m.
I would like to calculate the hydraulic grade line that tracks the pipe so that I can determine where a break tank may be installed to keep the pressure in the pipe acceptable (e.g. below 16bar). A pumping station will be installed in the valley to get the water back up the the last tank.
What information do I need and how do I go about doing this. I get stuck at step 1, calculating loss due to entry into the pipe from the first tank (0.5 v^2/g) as I do not know the velocity.
Please help, its been a long time since I did any hydraulics but its in my head somewhere.
Spainers
I have what should be a simple problem but I can't get my head around it.
I have a high level tank at elevation approx 1600m. A 350mm pipe runs down the valley to a low point of approx 600m and up to another tank on the other side at approx 800m.
I would like to calculate the hydraulic grade line that tracks the pipe so that I can determine where a break tank may be installed to keep the pressure in the pipe acceptable (e.g. below 16bar). A pumping station will be installed in the valley to get the water back up the the last tank.
What information do I need and how do I go about doing this. I get stuck at step 1, calculating loss due to entry into the pipe from the first tank (0.5 v^2/g) as I do not know the velocity.
Please help, its been a long time since I did any hydraulics but its in my head somewhere.
Spainers





RE: Calculate the location for a break tank
Here is a publication that has an example similar to your problem. See page 2.
http://www.nesc.wvu.edu/pdf/dw/publications/ontap/...
RE: Calculate the location for a break tank
I would like to include friction losses at pipe entry and in the pipe itself. Any help for expanding on the information given in your solution?
Thanks.
RE: Calculate the location for a break tank
estimate your pumping rate
estimate your pipe size and length
use any one of several equations to calculate the pipe friction loss (such as hazen-williams)
add that to the static to get the required pump head at the pump station
note that your hgl lines are drawing incorrectly
RE: Calculate the location for a break tank
RE: Calculate the location for a break tank
RE: Calculate the location for a break tank
I'm in asset management and we are proposing the installation of several break tanks to keep the pressure low (inlet to the break tank is via a valve and hydro turbine to power the pumping station(s) at the bottom.
Surely the large static head results in large forces in the pipe when the inlet to the break tank is closed?
I am quite comfortable with doing the two reservoir problems where the flow rate in a pipe between two reservoirs is calculated. Could I do the same for this problem but set the height of the second reservoir as H + Hf?
Thanks for your help
RE: Calculate the location for a break tank
The original consultant probably sized the 350mm pipe for the maximum fire flow capacity so the pipe velocity should be on the low side (with minimal friction). To determine the velocity, you need to know the maximum system capacity.
PRV's are also used to create pressure zones. If you have any users that are located on the hillside, you have a choice between using a PRV and installing a pump on the break tank. If you just use the hydro turbine, the discharge pressure would be too low for hillside distribution and you would forced to repump.
The choice between using a break tank and PRV depends on many factors, not just cost. You have considerations for fire flow, fire water storage, flow, size of system, etc. This is not a simple evaluation and you have not provided enough information to understand the application.
PRV's are generally reliable and you do not have to worry about them failing. You will have to do a Hazop analysis to determine the requirements for pressure relieving devices on the various tanks and pipe segments.
You will need to install a break tank at each elevation drop of 165 meters according to your proposed design concept. 165 meters of elevations equates to approximately 16 bar of pressure. You will probably understand why the original consultant used PRV's. It will be costly to construct so many break tanks, especially on a hillside.
RE: Calculate the location for a break tank
We are trying to add value to the project in addition to delivering original requirements e.g CSR, sustainability etc....
Your are right and we are in initial project readability stage but I am anticipating client questions.
I think your answer is perfect for now so I need to work from here. I will post back with clients comments for posterity purposes
Thanks all for your input