Air valve sizing

[JohnWeal]

Good evening all,

We have a submersible canister pump located some 9m deep in the canister. At normal river levels the water level is only 2m deep. The static lift to discharge from the canister is approx 10m.
So, when the pump stops, the water from the non return valve drains back to the intake channel level.
When the pump restarts, we have an air release valve at the top of the discharge elbow (it is actually a Tee with a blanked top lid)
It is a common design I guess to stop the water hammer effect because there is no resistance in the empty canister.
I am wondering, does the air valve allow some kind of back pressure by not allowing the air to escape too fast?

What is the ideal discharge velocity and hence the sizing requirements for this air release valve?

I assume also that there must also be a facility to vent so that a vacuum is not formed as the canister column of water drains out.

Regards
John

 

[bimr]

Most air release valves have two air release functions. There is a large orifice that releases large volumes of air such as when the pipeline is filling. After the large volume of air is released, this orifice is closed. A second orifice is then used to release smaller volumes of air.

 

[LittleInch]

Whether you needs to vent or not depends on your system and its susceptibility to air and the velocity of the water.

If your nrv is letting water back then it's not doing its job. Not enough information to decide.

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