Syphon effect calculation

[enguest]

Hello sirs,

I am working on the project which covers the modification of the existing produced water tank. Recently I have been asked to verify the size of the vent line, which is located on the overflow line of that tank. The main purpose of this line is to help to avoid the "syphon effect".

So could you please help me to find an industry standard or manual for calculation of "syphon effect"?

Thanks in advance.

 

[EmmanuelTop]

A rule of thumb is - the vent line size should be at least 50% of the line size through which liquid flows out and creates vacuum. In other words, if you have a 10" line discharging liquid from a vertical standpipe to atmosphere, you will need at least 5" vent line size on top of the line, to break the vacuum.

If you want to do a calculation exercise, it's fairly easy - the vacuum created will be equal to the liquid column height in vertical portion of the pipe, and certainly cannot be higher than absolute zero pressure. This setup can also be used for calculating required inflow of air (or gas), since you know the source (ambient) and receiver (pipe) pressure/vacuum, and the outflow of liquid. The two flows are essentially identical, as you are replacing the liquid volume OUT with the air volume IN.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[enguest]

EmmanuelTop,

Thank you very much for your help. But I need some type of standard to refer it in my calculations.

Thanks.

 

[rmw]

Do you have your Fluid Mechanics text book from your university days? You can find a lot of help there. If not, borrow one from a kid. I use mine often.

rmw

 

[StewPad]

Are you sure about the 50% role? - In a chemical plant it's completely the opposite - the vent need to be 200% then the biggest inlet

 

[EmmanuelTop]

I'm looking at some of the vessel datasheets showing 2" vent line and 3" drain size. It's in the same ball park.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[Compositepro]

If the purpose of the vent line is to allow vapor in or out to compensate for liquid level changes, then the 50% rule would be appropriate. If it is also intended to be an overflow line for liquid then the 200% rule would be appropriate (and then only if it is very short).