water pipeline design considerations

[ratash]

I have a water pipeline (several miles with hilly terrain), which takes treated water from a sump pump and dumps it into a separator for venting off the air, the water from there goes through a diffuser into a river. I have air release valves on the hill tops. The line is 16" ANSI 150 (operating pressure is 80 psig at 2500 gpm).

I have the following questions:

1) What is the purpose of the diffuser?
2) I see no back pressure control at the river. Does it need one and if yes, do I set it at one psig or so above atmospheric pressure?
3)My main question is what parameters are important to be considered in the water pipeline, as far as the hazards are concerned?

Thanks.

 

[chief]

The purpose of a diffuser at the pipe outlet is to entrain air in the water stream going into the river. The entrained air has a bioligal action on the water and helps to purify it.
Conversely the air vents on your hill tops are to remove accumulate air in the pipeline and prevent water hammer.
Securely support your pipeline, eliminate bends as far as possible, check for landslide possibilities,falling trees, seismic alllowance, and traffic across your pipeline if it is buried near road areas. Allow for thermal expansion /contraction ,if you have large variations in winter/summer temperatures. Insulate and heat trace if in Arctic area.

Offshore Engineering&Design

 

[ratash]

I looked up diffusers and didn't get such a simple to understand explanation.Thanks.

Do I need a back pressure controller?

 

[bimr]

"1) What is the purpose of the diffuser?"

A diffuser is typically used in wastewater applications to dilute the wastewater effluent into the river. A model may be required so that it can be demonstrated that the effluent is thoroughly mixed and diluted within the effluent mixing zone.

"2) I see no back pressure control at the river."

I don't think a backwater pressure would be required

 

[bimr]

http://cedb.asce.org/cgi/

http://WWWdisplay.cgi?5013678

 

[ratash]

Thanks.

No back pressure because we have air release valves. Correct?

 

[bimr]

You don't have to be concerned about back pressure because you have enough pressure head to keep water flowing into the river.

If you were pumping up to a reservior, you would probably want a check valve to prevent the water from falling back.

 

[stanier]

Go to

http://www.vetomat.com

for some detailed expalantions on air valve usage and placement. they also have software for designing the air valves. Look at their RGx range if you have contaminated water.

By the way air valves may mitigate waterhammer but they can also cause pressure spikes. The pipeline needs to be designed, including a surge analysis.

 

[ratash]

bimr & stanier, thanks for your tips and the site. I thought the back pressure valve is for preventing column separation.

 

[ratash]

stanier, I cannot find that site.

 

[bimr]

There is a discussion of outfalls in Metcalf & Eddy Wastewater Engineering.

What is the purpose of the separator? Is the separator at the river? Is this a cooling water line?

 

[ratash]

To get rid of the air before going to the river (required).

 

[bimr]

Not familiar with the use of a separator tank for this application.

If the separator tank is located ny the river and is open to atmosphere, then you will probably need a valve with level controller to prevent the separator from overflowing. Because the pipeline should have a higher head than the separator.

One would think that you have adequate velocity to force any air bubbles through the pipeline.

 

[ratash]

Thanks.

 

[cvg]

you probably should have combination air / vacuum release valves - not just air release valves to prevent vacuum when the line drains. Especially if you have no back pressure valve to prevent fast draining when the pump stops.

 

[ratash]

Thanks.

 

[stanier]

website

http://www.ventomat.com

has many good techinical articles on air valve location and sizing. Also Ventomat alllow the download of their selection software.

At water exhibitions you may find aestadgiving out free Cds with their Advanced Water Distribution Modeling and Management. this text covers the topic and can be used to determine if all the air valves are required.

 

[ratash]

Thank you so much, I will check it out. What is the name of the book?