Return pump size?

[kilnakorr]

I know this has been asked several times, with plenty of math and links to online calculators.

However, how do you calculate loss when splitting return to both refugium and uv filter?

Flow will obviously be different through fuge and uv, not to mention the use of 'feet' and 'gallons', when I'm used to metric system.

Is there an easier way to make a good estimate?

Tank is 90 gl with 30 ish gl sump.

 

[DCR]

The head is determined by the highest requirement of the three (return, fuge and UV). Assuming the fuge and UV are below the tank, the head will likely be determined by the return flow to the tank. I would suggest you take the elevation difference in meters and add about 1,0 to 1.5 meters for friction losses. For most systems this would put you around 2.0 to 2.5 meters of head required. For a 90 gallon, I would suggest about 5X turnover or about 1600 liters per hour for the tank. I would suggest a single DIN 25 (mm) return line or alternatively two DIN 20 lines for that flow. Not sure how much flow you want though your fuge and UV, but I am going to roughly estimate it might be another 800 liters per hour for each, so your total flow would be somewhere around 3200 liter per hour. Then you would look for a pump that will provide 3200 liters per hour at about 2.5 meters of head based on the head/flow curves or charts. If you are going with a DC pump you can oversize it and reduce the speed to get the desired flows. You can run DIN 20 lines to the UV and the fuge. I would make the discharge line and the manifold at least a DIN 25 and would recommend even a DIN 32 if you are using a controllable DC pump and want to minimize the speed and power. You want to include throttling valves on each of the circuits (return, fuge, and UV) to balance the flows, usually located on the discharge manifold

 

[kilnakorr]

@DCR
Thanks for the detailed reply!
All pipes are 1"/ 25mm (largest that will fit through the holes in the tank).
All three lines will have ball valves, so I can adjust flow through each (and cut off UV for maintenance/failures etc.) without cutting off return.

I will go with adjustable dc pump. Just didn't want to go way to big

I'll look for something that will do 3200L/h at 2.5 m, and make sure there's room for higher/lower flows.