Pipe Flow Calculations Forum

I have a pond where the water flows into a skimmer and is pumped out with a 1 1/2" line and a 0.2 HP pump at approximately 2000 gph (us). I want to add a sieve in between the skimmer and the pump. Water will flow into the sieve by gravity with a very minor (2" head) and will be pumped out of the sieve with the 1 1/2" pump line. My question is, what size gravity line do I need between the skimmer and the sieve? The opening for flow into the sieve is 4" diameter, however I would like to use 3" diameter flexible pipe if it will provide adequate flow.

What is the height difference between free water level and pump inlet. If pump is bellow water level, than it is ok to use 3" or even smaller pipe. If pipe is high from water level than it should be checked.

Anyway, for 2000 gph velocity is ok for both 4" and 3" pipe (less than 0.5 m/s). You can check it with pipe diameter calculator.

This small velocity means very low pressure drop.

Pump inlet is 4" above water level in pond and I am pumping against a 2' head. Thank you for your response.

Will 2000 gph velocity work for 2" pipe??

Yes