Pool drain velocity

[jimtheengineer10]

One of the requirements for a pool at a rv park is that the re-circulation system has to be designed so that velocities do not exceed 6 fps. Based on the pools size and that the entire volume has to be circulated every 6 hours I have determined that the circulation rate needs to be 118 gpm. There will be two main drains connected to one 1-1/2" diameter pipe that runs back to the mechanical room. How would I determine the velocity in this pipe? Thanks in advance.

 

[LittleInch]

Volume per second divided by Intrenal square area in the same units- I suggest feet. Or Google it

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[PEDARRIN2]

Since there would be the pool depth providing static pressure, this piping would be pressurized, not drainage.

A 1.5" Steel Pipe, at 120 gpm, would have a flow velocity of 18.9 ft/s.

A 1.5" Copper Pipe, at the same conditions, would have a flow velocity of 19.1 ft/s.

I would recommend increasing the drain pipe size back to the mechanical room or increase the circulation cycle to lower the flow.

 

[BigInch]

Seems that this is not a drain in the classic sense, but rather a suction line for the pump, in which case you should check the pressure drop of this rather small diameter pipe to ensure that there is sufficient suction head remaining at the pump inlet.

 

[PEDARRIN2]

It has been awhile since I did a pool design, but if I remember correctly, the pool drainage is directed to a large sump where the pump is located. I do not know if the drainage pipe is connected directly to the pump. I would be concerned about the extra "negative pressure" being exerted on the drains in the pool. They should be specified with "vacuum breakers" to prevent anybody from being held in place under water - so it might not be an issue.

Anyway, at the flows suggested, the pipe is too small for the maximum velocity.

 

[cvg]

this is recirculation line, suction to the pump. 1 1/2 inch pipe is way too small. You need at least 2 1/2 inch pipe. Inlets should have an anti-vortex cover to prevent suction entrapment

https://www.maricopa.gov/EnvSvc/AboutUs/pdf/C6S3.pdf

 

[bimr]

Agree with cvg except it should be a 3-Inch diameter pipe (velocity of 5.1 ft/sec). O.262 cfs/(((3.068/12)/2)²*3.14)

The hazards of pool drains have been known for some time:

https://www.nachi.org/pool-drain-hazards-inspection.htm