Drain and return

Van Eternal · Mar 5, 2021

Hi guys ,

This might be a silly question but can't get my head around it and trying to prepare as much as I can before i start my tank.

I have a aqua one reef 300 ( 300 litres and 90 litre sump) and the drain pipe size is 40 mm ( i believe thats 1 1/2 inch) and a return pipe size of 20 mm (3/4 inch?). Im trying to calculate the drain flow rate and ways to control it. Therefore my question is: Is the flow of the drain pipe controlled by the return pump in a way? Say for example my return pump will be set at 900 litre an hour, therefore the amount falling to the sump cant be greater than 900l/h as my pump is only pumping 900 litres/h to the display tank. Is that the right understanding or am i missing something ?

Sorry if this doesn't make sense trying my best to explain

CMMorgan · Mar 5, 2021

Van Eternal said:
Hi guys ,

This might be a silly question but can't get my head around it and trying to prepare as much as I can before i start my tank.

I have a aqua one reef 300 ( 300 litres and 90 litre sump) and the drain pipe size is 40 mm ( i believe thats 1 1/2 inch) and a return pipe size of 20 mm (3/4 inch?). Im trying to calculate the drain flow rate and ways to control it. Therefore my question is: Is the flow of the drain pipe controlled by the return pump in a way? Say for example my return pump will be set at 900 litre an hour, therefore the amount falling to the sump cant be greater than 900l/h as my pump is only pumping 900 litres/h to the display tank. Is that the right understanding or am i missing something ?

Yes and no.
Yes... it is obvious that you are limited by what your pump can return.
That said, controlling the flow also relies on a gate valve of some sort coming from the overflow. Using a 1.5" overflow is fine and possibly even quieter. You just need to dial in the flow with a little trial and error. You would be doing this either way.

mdb_talon · Mar 5, 2021

Personally i would never adjust the rate of return from overflow and unable to understand why you would want to. I have a gate valve on mine so i can shut it off in some scenarios(pump also off)

As for question of the OP yes it your pump pumps 867 gph then the return will have 867gph going through it. The one key thing is ensuring that your pump is not sized above what your returns can handle. If you pump does 1000gph and your return can only handle 850 then you gonna have wet feet. If it is a DC controllable pump it is a lot easier and u can adjust if it is too much.

RocketEngineer · Mar 6, 2021

OP, you are correct in that if the pump pushes 900lph up to the display, only 900lph is going to drain to the sump. That’s basic physics.

Placing a valve on the drain lines is for a different purpose and carries some risk that needs to be handled. The purpose is to reduce noise by ensuring the drain with the valve is full of water. However, to do this safely you must have a second drain. This second drain pipe has NO restriction and is the backup in case something clogs. This is known as a Herbie drain configuration.