Overflow box size

[mark freshwater]

Hi
Im looking at the http://www.marine-sources.com/product-showcase/overflow-system/
They come in 2500lph or 5000lph, my tank is 270 litres and my sump 3x15x15 ,
and my return pump 3000lph with a 3.5 metre head height.
i have read that your overflow should match your overflow in lph ,
my question is that the smaller overflow has only 1 outlet where as the bigger overflow has 2,
i like the idea of 2 incase one gets jammed etc.
Would running the bigger one cause problems ?

 

[miPapareef]

The bigger one is going to better for you, like you already said that second outlet will bring some redundancy if the first one plugs or restricts.

Yes return flow and overflow must match, but there are two ways to achieve this. People use one or both of these approaches in almost all sump setups.

1. Add a valve on the return pump outlet to lower return flow to match drain, or
2. add a valve on the primary drain line to match the return pump flow.

As for that larger overflow being too big, you should use approach #2 and add a gate valve to the primary outlet so you can tune it to match your return pump flow.

 

[mark freshwater]

Excellent advice , thank you , i ordered the bigger one just now.

 

[mark freshwater]

Also in regards to plumbing the overflow , would i use the same dimension pipe that fits to the bulkheads on the box?
Or would i use a coupler to expand the pipe size ? So say if the bulkhead is 1" , should i go with 1" pipe , or get a 1" to 1 and a 1/2" coupler and run 1 and a 1/2" pipe etc