Water transmission main 2

[IMNO]

Hey,
I would like a ask a query regarding designing of gravity water transmission main. most often the available ground slope is quite steep and if the pipe is laid on that slope then the flow carrying capacity is increased hence the water starts flowing partially in the pipe then at certain point ground slope is mild thus flow becomes full.
so at this situation should we change the pipe diameter at steep slopes to ensure the flow remain full?
what would be the case if we use the same pipe through out (both a steep slope and mild slope)?
what about air and its impact in the this partial to full or full to partial flow condition? how to tackle this?
In case of partial flow does the air release valve works?

 

[BigInch]

It is water vapor, not air, that is in the space over partial flowing pipes. Where pressure increases above the water's vapor pressure the water vapor pocket collapses and flow becomes full across the section. There is no air to be released. Entrained air coming out of solution is another problem. That's where you will need air release valves.

The problems related to cascade flow are the increased velocity on the bottom of the pipe, undulating, unstable flows (on the critical slope), surge pressures and internal hydraulic jumps which may vibrate the pipe, or increase wear and erosion of the pipe wall.

 

[cvg]

depending on the design you may well have trapped air, entrained air as well as dissolved oxygen within the water. Pipe size does not need to be varied.

http://www.syntecpe.com/pdf/AirinPipelines.pdf

 

[bimr]

Water transmission mains should be designed for full pipe flow. Otherwise, you will have problems with contamination, water hammer, etc.
See the upload.

 

[IMNO]

Thanks for your answer.

Actually, I saw the deisgn of effluent pipeline having maximum flow rate as 20 ft3/sec and minimum flow rate as 6 ft3/sec.
The lenght of pipe is about 20 km in length and double acting air release valves are provided at specified interval say, every 2000ft.
The profile of pipeline is showing continuous drop and at some location, pipe is going down and than up (as incase of inverted siphon)and than again running of certain slope.

when i calculate the the flow carrying capacity of the pipe based on the slope on which it is laid, the capacity came out to be more than 20 ft3/sec, say 30 ft3/sec, which indicates that the pipe will not be flowing full except the inverted siphon .

1- Now i want to analyze the effect of water hammer, hydraulic jumps and the effect of partial to full flow or vice versa? how to do that?
2- Will Air relase valve work incase of partial flow in the pipe?

 

[coloeng]

If you control the flow at the terminus of the pipe you can force it to flow full and you won't have to worry about hydraulic jumps, etc.

 

[bimr]

What is the range of elevation that you are working with. Do you have a profile? Is this a sewage forcemain or a water transmission pipeline?