Tank Venting

[99491]

Once you have calculated the total inbreathing and outbreathing of the tank how do you then determine what size vent you should use if you are using a open swan neck breather.

 

[Chance17]

To 99491: I use pipe friction/flow calculation.
This can be software or a manual method such as the Crane Technical Bulletin.
The swan crane vent is modeled as pipe. First assume a pipe size.
The model has 1)entrance loss, 2) length of pipe for nozzle, 3) 180 deg return bend 4)exit loss.
The entire model should handle the vent flow and have friction loss less than relieving pressure.
If not, increase the pipe diameter.
The method works for both pressure and vacuum.
If there is a bug screen on the exit, some additional safety factor should be added -- could be one pipe diameter larger.

 

[JStephen]

Calculate required venting rates. Calculate allowable pressure using Appendix F of API-650 in order to determine the allowable overpressure during venting. Then refer to the vent manufacturer's flow charts for vent sizing.

API-650 requires venting per API-2000. And API-2000 requires that vents be flow-tested. So technically, you can't meet the requirement just by calculating flow rates without flow-testing (except for lifting-cover roof manways, that is.)

The ASHRAE handbooks also have flow information for various fittings (including screens) that can be applied to tank vents.