Overflow Pipe Sizing

[Chem2020]

I am trying to size an overflow pipe line for Atmospheric tank. I know I can not size it based on inlet flowrate.
I need a good explanation why overflow pipes can not be sized based on inlet flowrate. The overflow discharges to ground. Some one was arguing to use the vent as an overflow to mimimize the cost, but you can not use the vent as an overflow. I am confused.

 

[GHartmann]

There is no reason not to size the overflow on the basis of the inlet flow. Maximum outflow (overflow) has to equal maximum inflow. The only restriction is the lower pressure drop needed in the overflow line.

Good luck.

 

[TD2K]

I agree with GHartman. What is the purpose of the overflow line? It's to prevent your tank from overfilling which means to me that the line has to have a capacity equal to the inflow.

 

[MJCronin]

This topic has been discussed before in other fora

http://www.eng-tips.com/viewthread.cfm?qid=214602.

Even the slowest among us should recognize that pumped flow INTO the tank follows different rules than self venting gravity flow OUT FROM the tank overflow

(Hint: the Froude number is the key !)

It is not clear to me what "sized based on inlet flowrate" means in the original post.

Do you mean that the overflow and inlet pipe line size must be the same ?

(You may want to consider posing your question in the STORAGE TANK forum)