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saxman2u

- 19

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I am trying to calculate how much water can flow with just gravity from water tank A to water tank B. Each tank as a 2" orifice on the side wall at the bottom. If water tank A is 100% full and water tank B is completely empty, if someone opens a 2" ball valve at the bottom of tank A, how many GPM's flow through a 2" SCH40 PVC pipe that is 50 feet long? no elbows, just straight pipe. Both tanks are 12 feet high and 12 ft diameter. Tank A is 50% full with water 6 feet higher than the orifice. Let's also say the orifice of tank A is short tube with Cd=.81 I am just curious about the max flow when tank A is pretty much full or the first 60 seconds of flow after someone opens the 2" ball valve.

I https://www.haywardflowcontrol.com/assets/documents/flowcontrol/pdf/VessFlow.pdf where the water is 6 feet higher than the 2" orifice and calculated that about 150 GPM can flow out of the vessel if someone opens or drills a 2" hole in the tank. Can someone please confirm i did this math correctly, https://www.haywardflowcontrol.com/assets/documents/flowcontrol/pdf/VessFlow.pdf . What I don't understand is what does friction loss or a 50 ft piece of 2" SCH40 PVC pipe do to that flow of 150 gpm? I thought that 2" PVC pipe can handle around 55 GPM with low pressure and water traveling 6 ft/sec. How can 150 GPM flow out of a 2" opening in a tank but tables out there show that 2" PVC pipe can only handle 55 GPM (link here about flow rate through pipes)? is it because the 6 feet of water in the tank is increasing the velocity of the water therefore more water can be shot through the 2" pipe?

Finally, if the tanks keep there 2" orifices and their 2" ball valves, and I remove the 50 ft of 2" PVC pipe and install 3" PVC pipe instead to minimize friction loss, does this really improve the flow or GPM and how much faster does tank B fill up at peak flow when tank A is full during the first 60 seconds? Is it worth it to spend more money on bigger pipe and labor??

Thanks,

-S