sump flow rate & pumps

[mzcjjj]

Greg,

I just reviewed your three part article on sumps in Reefkeeping and I thank you for sharing your knowledge. I have a few questions if I may.

I have a 175 bow front oceanic tank. It has two overflow boxes each with a one inch drain and a 3/4 inch return. I am planning the sump which will go underneath the tank in the cabinet. I can fit a 50 gallon sump (~36 X 18 x 18). There will space in the cabinet (in addition to the sump) for external return pumps if need be. I estimate I will have 7 feet of head (5 vertical feet and 2 feet estimate of pipe bends and drag)

1) I estimate that each drain should drain from the tank about 600 gph. Do you think this is reasonable? I have heard estimates that range from 300 - 1000 gph for each 1 inch drain.

2) I am planning on two return pumps, one to each return in the overflow. Is this reasonable or is it better to have one larger pump and split the return to the overflows?

3) Assuming 1200 +/- gph flow through the sump is it best to have the return pumps inside the sump (submersible) or external to the sump connected by bulkheads?

4) since the drain flow rate is a guess and the actual pressure head is a guess, what size pump(s) would you recommend for this setup?

Thank you very much for your tiem and expertise.

Chris

[gregt]

1) I estimate that each drain should drain from the tank about 600 gph. Do you think this is reasonable? I have heard estimates that range from 300 - 1000 gph for each 1 inch drain.

You may have some issues with noise at that rate, but it's doable.

2) I am planning on two return pumps, one to each return in the overflow. Is this reasonable or is it better to have one larger pump and split the return to the overflows?

The upside to two pumps is redundancy. If a pump fails you aren't out of luck. The downside is extra cost and space. I've had two pumps on most of my tanks. My latest tank only has one return pump but it is the same type of pump that is on my skimmer and my closed loop so they can be interchanged in an emergency with minimal effort.

3) Assuming 1200 +/- gph flow through the sump is it best to have the return pumps inside the sump (submersible) or external to the sump connected by bulkheads?

I can't think of how it would really matter. An external pump will transfer less heat to the water. But that is true regardless of the flow rate.

4) since the drain flow rate is a guess and the actual pressure head is a guess, what size pump(s) would you recommend for this setup?

Bigger is better. You can always cut the flow down with a valve, but you can't make the pump push more water.

[mzcjjj]

Thank you very much for your quick response.

Since the flow rate is governed by gravity I do not see that I have any control over it. I therefore must take whatever flow rate I have and match the pump to it. It that not correct?

[gregt]

That is true to some degree. But it's not usually that simple. You can put a lot of water through two 1 inch drains. However, it may result in noise levels that are unreasonable. I've put over 1000 gph through a 1" pipe before, but it was impossible to keep quiet.

600 gph might take some work, but it's doable.

Like I said, a larger pump can be throttled back if the drain can't keep up, or it's too noisy. A smaller pump can't be made to pump more water. The best way to tune for max flow is to be sure the pump is big enough and cut it back if necessary.

[mzcjjj]

thank you again. I very much appreciate it.

Chris

[gregt]

No problem. Let me know how it turns out.