Forced air flow in pumped outfall

[StephenA]

I put this question in a different forum and got no replies, This forum looks more appropriate. Apologies if duplication annoys anyone.

We have designed an outfall with pumps well above sea level. When the pumps stop the sewage level drops to sea level. That cannot be changed.

Normally the pumps would be started slowly to allow the air to back up and release through an air valve close to the pumps.

The client wants to start the pumps at full rate which will trap the air and force it out through the offshore end of the Outfall.

The question is how do I calculate the flow rate required to carry the air down the outfall and out through the diffuser?

Stephen A

 

[aussiemike]

Hi Stephen.

It sounds like a problem you would like to design out if you can.

Can you allow the outfall to flow by gravity (bypassing the pump station) until the effluent pipe flows full and backs up into the pump chamber? This would ensure the pipe was full of effluent before the pump starts.

We used this design on a twin 1000mm diameter outfall in Australia.