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david6245 (Chemical) (OP)
30 Aug 10 14:54
Hello,

I need to determine whether a 275 psig steam drum will require a vortex breaker at its bottom nozzle that goes to the suction of a pump. I have a 12" outlet nozzle and suction line to the pump. The flow rate is 1,600 gpm. Liquid level in the drum is about 5 ft above the bottome nozzle, and the bottom nozzle is 20 ft above the pump suction nozzle.

Can anyone share any guidelines/rules of thumbs/references for this?

Thanks in advance,

David
JJPellin (Mechanical)
30 Aug 10 17:25
I have heard and used the rule that submergence to avoid vortex problems should be at least 1 foot for each foot per second of velocity at the nozzle.  For your example, 1600 gpm passing into a 12" nozzle, you would have about 4.5 feet per second velocity entering the nozzle.  This assumes schedule 40 pipe.  Thus, you would want at least 4.5 feet of submergence.  That could be cutting it a little close.  I would consider adding a simple vortex breaker in case the flow could be a little higher than design or the level a little lower than design.  

I found this same value (1 foot per foot per second) in Cameron Hydraulic Data related to submergence for side intake dry pit pumps.  
 

Johnny Pellin

StoneCold (Chemical)
31 Aug 10 11:31
If I am lucky enough to be designing a new tank, not recycling an old one, I always put the vortex breakers in.  They are cheap insurance.

Regards
StoneCold
casflo (Mechanical)
2 Sep 10 8:39
You can use the following equation from the ANSI/HI 9.8-1998 "Hydraulic Institute´s Pump Intake Design" that is:
S = D + 2.3DFr
S is the minimum required submergence to avoid vortex formation.
D is the nozzle diameter and Fr is the dimensionless Froud number, Fr = V/(gD)**0.5
V is the nozzle flow velocity and g the gravitational acceleration.   
Shmulik (Mechanical)
2 Sep 10 11:45
thread124-156148: vortex at the tank outlet

You may refer to "Pressure Vessel Handbook", Megyesy, Vortex Breaker (page 320, 12th edition).
 

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