Estimated Pressure for Water Distribution Pipeline 4

[billbracken]

Hello All,

I'm here with the start of a couple projects involving the distribution of water across land via pipeline. Before I start, I need to find the estimated pressure the line will have on it to determine the type of pipe to use for my project. Ideally, i'd like to come up with a formula and/or equation for calculating the pontential pressure the line will run at.

All viables that will be in effect would be;
- vertical height and distance the line will be running
- pump curve
- pipe size
- friction loss of the pipe
- ability to achieve (non-designated) gallons per minute

Without going into too much detail, can we create a formula to determine the psi of the line? If there is any other factors that would have an effect on this, please feel free to add.

 

[bimr]

You seem to have left out economics.

A transmission line typically flows at an economical velocity of 3-5 ft/sec.

Ordinarily, comparative analyses of initial cost plus energy costs over a 20-yr (or longer) period would be made for two or three pipe diameters to select the optimum.

 

[amlinerrichard]

You can't do too much till someone decides how much water you need to transport. 50 gallons for 2 miles is a small car with 10 5 gallon buckets in the back seat, 5000 cfs for a 25 mile trip is a different ball game.

 

[billbracken]

Let me provide an example:

There's two ponds located in a hilly region, represented by "Pond A" and "Pond B". Pond A sits at an elevation of 4,800ft. above sea level, with a depth of 30ft, holding approx. 1 million gallons of water. Pond B's water supply has been deminished and would need to be refilled. Pond B sits at 4950ft above sea level, holds .5 million gallons of water and located exactly 1 mile from Pond A. In between both ponds, two hills rise, both 5,300ft at their peaks. The water pump at pond A needs to acheive 4,200gpm within 300psi. The calculated psi will determine which type of pipe is to be used to the project. In this example however, we can use 10" HDPE pipe that will be run for 5,280ft.

 

[bimr]

As noted above, your pipeline should be sized for 3-5 feet per second. This is straight out of Cranes Technical Paper. For 4200 gpm, that means you need a pipe 18 to 20-Inch diameter. See the results from the online calculator.

A 10-Inch pipe will not allow the water to flow economically and will generate a headloss of approx. 150 psi.

 

[cvg]

try bernoulli equation

http://www.pipeflowcalculations.com/pipe-valve-fitting-flow/flow-in-pipes.php

 

[billbracken]

Hmm. In hydraulic fracturing practices, they source water very similar to example explained. Their pipe sizes run from 8 to 12" HDPE pipe. Given the range of 8", 10", 12" pipe with needing the ability to pump up to 4,200gpm, I know it can be done. Yes, their methods may not be the most efficient however with any kind of water distribution like theirs, they would need to calculate the psi the line will at first before deciding which type of pump to use (based off pump curve data). Now my question is, can we write a mathematical formula to calculate their psi, as it is very similar to my project?

 

[bimr]

Use Darcy-weisbach equation:

http://www.engineeringtoolbox.com/darcy-weisbach-equation-d_646.html

 

[coloeng]

If economics is not an issue, why don't you just hire a civil engineer to do this work for you. Get away from the learning curve and have it done professionally.

 

[cvg]

you have been given the formulas
here is an example

4200 gpm through a 12 inch pipe will flow at 12 fps
you have 500 feet of static head
assuming C=140 and half mile to the top of the high point you will have about 80 feet of head loss
assume another 5 feet of minor losses
total head at the pump discharge is 500 + 80 + 5 = 585 feet of head
density of water is 62.4 pcf
pressure is 585 x 62.4 / 144 = 254 psi
with such high velocity flow, you can expect transient pressure spikes on pump shutoff or loss of power
so you will need to do a transient analysis to estimate the pressure rise caused by water hammer
you would need the highest grade PE material and DR 7.3 pipe.

going to a 16 inch pipe you could reduce your pressure by about 25 psi, transients would be reduced, pipe would probably be the same

 

[bimr]

Assuming a power cost of $0.10 per kW and operating 12 hours per day for a year, the difference in power cost is approximately $750,000 per year between and 18-Inch and 10-Inch pipes.

In addition, you would have the equipment and utility costs to install a 600 HP pump as compared to a 50 HP pump.

 

[rconner]

Be very careful in hydraulic calculations and pumping analyses also with the inside diameter of the actual pipe you are dealing with -- some plastic pipes have smaller inside diameters than other types of pipes. In long-term Engineering Economic analyses, and even when very smooth (e.g. laboratory, or field unproven?) flow coefficients are assumed, the energy consumption and "power pumping cost" can be very surprisingly higher. In other words in modern water piping systems with hydraulically smooth pipes or linings, you can basically get more/easier through a larger hole.

 

[dicksewerrat]

HDPE pipe is sized by outside diameter.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[katmar]

In a simple case the delivery pressure (what you have termed "the psi of the line") is just the sum of the friction head (given by Darcy Weisbach formula) and the static head (rho x g x h). But in a more complex situation like the one you describe there is likely to be slack flow and the installation of air vents will reset the pressure to atmospheric in places. This necessitates evaluating the pipeline in separate sections.

The range of possible pipe sizes will be relatively narrow - defined by rules of thumb for flow velocity and permissable materials of contruction. You have to do the entire calculation, determining the point pressures along the route for each pipe size. Once you get into this exercise it may become obvious that a single pipe size is not the correct solution for the entire length.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[Overbudget]

If you want to know the pressure in the pipe at any point, you need to plot the profile of the pipe and the profile of the hydraulic grade line. It sounds like the pipe profile goes up and down, while the HGL of course is high at the pump end and meets the pipeline profile at the discharge end. The difference betweent the two lines at any point is the actual pressure in the pipe at that point. This type of analysis will also help you identify any intermediate high points that could cause problems. It might be necessary to select the pump to pump to an intermediate high point instead of the end of the line. You could end up with parts of the line flowing by gravity. For any pumped line going cross country it is necessary to go through this exercise.

You can use the formula above, the Hazen Williams equation, or charts provided by the pipe manufacturer to get the friction loss/100 feet at a given flow, and find the slope of the HGL. Start at the discharge end and project it back to the pumping end at this slope. Plot the ground surface from survey or topo maps. Depending on your assumptions and your level of detail, this can be a rough estimate or a detailed analysis!

 

[Abdul1987]

Dear Sir,

Great discussion! Appreciated! I am new here but I am very enthusiastic to develop my knowledge skills through it. Recently, I am confuse with my research thesis for my master degree where I need to evaluate one water supply distribution network in terms of leakages through Epanet software. For this I need to calibrate and validate the model (Epanet) where I have necessary data (flow+pressure) for calibration and validation at six different locations but don't know how to do? & what is the ease and standard way to calibrate the model and how actually the leakages can be found? Last but not the least, I am looking for emitter coefficients table because I am confuse in its unit as my flow is in m3/day and pressure in (m), so emitter coefficients guess values would be? for pipes: 50mm, 80mm, 100mm & 150mm? Please your kind assistance can led me graduate and attained my goal on time. Thanks for everything in Advance and looking forward for your valuable suggestion, help and advises. Regards, Abdul Rahman.