All,
I'm new to this valve engineering. Although I've asking to my seniors and reading many materials, I'm yet unclear about the operation of air release valve.
Hope my friends will help me out. Whats it principle behind its operation?

For waterlinea: generally ball float to close opening when water level reaches valve top for mains when filling with water (air out) and float opening again for vacuum release when emptying pipeline (air in).

Combined types have in addition a separate, considerably smaller float and opening at a higer level to let collected air on top point of pipelines (valvetop. Purpose: to let smaller amounts of collected air escape under pressure before and without main float opening (pipeline is filled with water under pressure below collected air).

See for instance http://erhard.de/index.php?Air-Valve-TWIN-Air-Valv..., or references given by stanier on your former posting. It is always a good idea to search what is available from suppliers on net.

So. Basically its operation is during when the line is filled or when it is drained. Does it have any role in handling surge? Also Where can it be located? To a highest point in system or anywhere?

Answers.

1. Yes, but as mentioned letting off collected air under normal operation (from contained air in water) must also be considered.

2. No. Search this forum or others/net for earlier discussions on waterhammer.

3. Highest points if several ups and downs.

4. Additional vacuum breakers may be necessary for high falls or certain circumstances. For instance water mains with large diameter and higher level differences or hydroelectrical water lines to turbines. (Largest vacuum breaker I have been involved with was 800mm, 10 bar class, constructed as a spring balanced disc for hydroelectrical turbine water feed line)

Oh Oh Oh.. Thats a huge data. And thanks for clarifying that it doesn't involve in surge.
But in my project where I'm dealing with pumping system, We are having an air vessel with an air releae valve in a pump room. This pump room is at underground floor level. I doubt about its operation. My senior told me that it will be handling surge. I'm confused. Then they came up with new valve called Pressure Release Valve. Again going back to zero. What does it do??

Air valves primary purpose is line filling and drainage. It is a myth that they universally aid surge mitigation. They can indeed aid mitigation if they are sized, positioned and of a type that coorectly fulfil this function. However there are many instances where they actually contribute to surge events when incorrectly selected.

As I said before some have restricted orifices. Others have multiple orifices. Some are designed for sewage others are not. If you are relying on these devices to mitigate surge then they have to be treated with the same respect as a relief valve. They need to be registered, maintained and regularly tested.

That is why you just dont go and buy a "blue" one from some merchant. You have to work with the manufactuer if you do not have the skills to engineer the pipeline yourself. By respected valves like Ventomat.go to www.ventomat.com and read their technical articles.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/

• http://files.engineering.com/getfile.aspx?folder=55c6ec3b-ea8c-4cc1-9d07-4d