CAV vs. ARV for sanitary sewer force mains 2

[rnair95]

Hello,

I am new to this forum and was wondering if I can get some advice about the pros and cons of using CAV over using ARV? I am proposing a mile long forcemain using HDPE. The forcemain starts at a pump station and terminates at wastewater treatment plant.

 

[ccampttu]

This might help.

http://www.gaindustries.com/products1/bulletins/airvalves/Air_Valve_Bulletin.pdf

Curt

 

[bimr]

Assume you mean combination air release on a force main?

 

[bimr]

Here are a couple of pages of articles that disuss the topic.

You should avoid the CAV if at all possible unless the CAV is needed to protect the pipe from vacuum collapse.

If this is a force main, you should try to avoid the ARV's if possible and use manual air release.

Refer to the articles.

 

[rnair95]

I am actually working with a consultant on this project and they are proposing to use CAV. This forcemain is located near marshland and there is not enough fall between the pump station and the wastewater treatement plant. I presume they are proposing this to prevent vacuum collapse.
What are recommended measures that can be done to release air accumulating in the force main near high points?

 

[bimr]

The most important measure that you can do is to maintain an adequate velocity (over 4 ft/sec) that will force the air downstream. The article discusses this in depth.

 

[sjohns4]

Air Release will expell air at a controlled rate. This helps minimize surge pressures when the pipe is filling.

Air/Vacuum Valves expell large amounts of air quickly when the pipeline is filling, and will allow air to enter the pipeline to prevent a siphoning or negative pressure conditon, but once the initial filling of the pipeline is completed they shut off and will not exhaust air that may accumulate over time at a high point.

Combiniation valves will serve the function of both valves above, and if there is ever a question these are what I tend to default to. I never do a strictly Air/Vacuum valve...should an operator change a set point or something else at the pump station it would be easy for the pump to suck some air near shutoff and airlock the pipe over time.

Usually the cost of Combination ARV's is minimial in the overall cost of the force main and I tend to err on the side of caution and place more than fewer, if there ever is an air problem in the force main you and your client will have much more $$$ in troubleshooting than the valve cost to put in in the first place.

As previously mentioned, keeping the velocity to around 4 fps is a good idea, and at a minimium 3 fps, even though most state regs say 2 fps.