Matching O/F vs return flow rates

[Barro777]

Merry Christmas, everyone. I continue with my noob questions. This one is about matching the overflow vs return pump flow rates.

I am planning to get Mag 5 for return and Eshopps 300 for the overflow. At 3' discharge head Mag 5's flow rate is 375 gph, while Eshopps 300 is, well, 300 gph.

Should I be worried? Should I get a Mag 3 instead, or conversely, a bigger overflow?

[jimmyj7090]

The overflow always needs to be able to handle more than the pump will be pumping.

The return rate to the tank is controlled by the pump. The overflow rate is exactly the same as the return rate because it is determined by the return rate. Pump up > gravity down (unless the overflow can't keep up in which case you have a flood). In other words, If the overflow itself cannot handle the return/drain rate then the tank overflows.

To run 375ghp return rate you will need a larger overflow (or you can restrict the OUTPUT from the pump to slow it down to something below 300gph).

[Palting]

Sounds like you haven't bought anything yet. For a 40 gallons, I would get an oveflow that can handle at least 400 or more. Any thought to drilling the tank? Your planned pump is fine.

[jimmyj7090]

I second the suggestion to consider drilling the tank :)

[nlgill13]

Drilling the tank will make things a little more simple in the long run

Good size pumps, just remember that you are going to have headloss due to turns in the piping (90 degree or 45 degree fittings) and fiction.

You can control flow rate with ball valves on either side of the sump (check out pic below)

[Barro777]

No, I haven't bought anything yet. Want to do my research first best I can ))

A ball valve... you gotta correct me here if I am wrong, but really, from the point of view of physics, ball valves do indeed restrict the orifice, but, with the pump's discharge rate remaining the same, what happens is the velocity increases, meaning the same amount of water gets faster through the restricted opening, with the flow rate remaining pretty much the same.

But that aside, every time I talk overflow, the drilling option comes up. If I were to drill the tank, what size opening do I want to drill? And I would obviously want some kind of a screen on that opening, right? To prevent stuff (like fish) from getting into the drain line. What should be the size of that drilled opening, and what should I use for a screen?

I am sorry, I'm really new at this, so just bear with me here please ))

[C0rp]

If you put a pvc ball valve on the output of the return pump, it will INDEED restrict the gph flow rate of the pump, depending on where you set it.

[Ron Reefman]

No, I haven't bought anything yet. Want to do my research first best I can ))

A ball valve... you gotta correct me here if I am wrong, but really, from the point of view of physics, ball valves do indeed restrict the orifice, but, with the pump's discharge rate remaining the same, what happens is the velocity increases, meaning the same amount of water gets faster through the restricted opening, with the flow rate remaining pretty much the same.

But that aside, every time I talk overflow, the drilling option comes up. If I were to drill the tank, what size opening do I want to drill? And I would obviously want some kind of a screen on that opening, right? To prevent stuff (like fish) from getting into the drain line. What should be the size of that drilled opening, and what should I use for a screen?

I am sorry, I'm really new at this, so just bear with me here please ))

Don't worry about asking newbie questions, those of us who know the answers (or assume we do) are just trying to help. I was in your position once and I didn't know RC existed, so count yourself as lucky.

The ball valve will decrease flow rates. The water velocity changes very little. I don't understand the physics, you'll just have to trust us. And if you are using pvc pipe in your system, get a ball valve that has unions built into the ends (Lowes has them, my HD doesn't).

A 300gph flow rate for the siphon overflow is OK. And you can restrict the flow from the pump to match it. However... if you are considering drilling the tank (and I would NEVER build a new system without drilling) you can pick the flow rate you want. I think RC has a bulkhead size to flow rate calculator somewhere. I think a 1" will flow 600gph. That would be great and you can run your pump wide open. The screen you asked about is dealt with in a variety of ways. The first thing you want to do is look at the BeanAnaimal overflow (search for it here on RC or you can Google. And let me HIGHLY recomend that you do the 'spare' or 'emergency' drain as well. It's the best insurance.

Good luck.

[jon99]

However... if you are considering drilling the tank (and I would NEVER build a new system without drilling) you can pick the flow rate you want. I think RC has a bulkhead size to flow rate calculator somewhere. I think a 1" will flow 600gph. That would be great and you can run your pump wide open. The screen you asked about is dealt with in a variety of ways. The first thing you want to do is look at the BeanAnaimal overflow (search for it here on RC or you can Google. And let me HIGHLY recomend that you do the 'spare' or 'emergency' drain as well. It's the best insurance.

Good luck.

I second that!! I know drilling a tank may sound a bit scarry when you are first starting out, but trust us, it's the way to go. Do a search on here, there are step by step instructions even videos on showing how to do it. After you drill your first hole, you'll realize how easy it was and you likely want to just keep on drilling! Here is the calculator that Ron was referring to http://www.reefcentral.com/index.php/drainoverflow-size-calc
Basically you enter the flow rate of your return pump (375 in your case with the mag 5) and it will tell you the size of the opening you need to drill for the drain, always round up to be on the safe side. I would also recommend doubeling up on the drains ( 2 X 1" holes/drains). This may sound like overkill, but if for some reason one gets clogged, algae, snail, dead fish (hopefully not the last one) you have a back up drain that can handel all the flow from your return pump and avoid a flood.

As far as building the overflow itself, I went with a cheap and simple approach. Check out the pic. It's simply a PVC elbow that skims the water from the surface. It's smaller that bulkey boxes, the tank is drilled near the top rather than the very bottom (incase the bulkhead leaks, and the entire "overflow kit" cost less than $20.

http://www.reefcentral.com/forums/picture.php?albumid=5097&pictureid=35417
http://www.reefcentral.com/forums/picture.php?albumid=5097&pictureid=35416

[Palting]

But that aside, every time I talk overflow, the drilling option comes up. If I were to drill the tank, what size opening do I want to drill? And I would obviously want some kind of a screen on that opening, right? To prevent stuff (like fish) from getting into the drain line. What should be the size of that drilled opening, and what should I use for a screen?

I am sorry, I'm really new at this, so just bear with me here please ))

Don't apologize. Just ask.

An open elbow drain makes me afraid it's too easy for something to fall inside the pipes. Here's a link to a complete glass hole making kit. Has the cutting head, plus all the plumbing. The overflow box will help keep fish, snails, hermits, etc, from going down the drain. http://glass-holes.com/Complete-Overflow-Kits_c3.htm I wouls suggest thhe 700gph kit. Better to have more drainage capacity than you need.

[jimmyj7090]

I second that!! I know drilling a tank may sound a bit scarry when you are first starting out, but trust us, it's the way to go. Do a search on here, there are step by step instructions even videos on showing how to do it. After you drill your first hole, you'll realize how easy it was and you likely want to just keep on drilling! Here is the calculator that Ron was referring to http://www.reefcentral.com/index.php/drainoverflow-size-calc
Basically you enter the flow rate of your return pump (375 in your case with the mag 5) and it will tell you the size of the opening you need to drill for the drain, always round up to be on the safe side. I would also recommend doubeling up on the drains ( 2 X 1" holes/drains). This may sound like overkill, but if for some reason one gets clogged, algae, snail, dead fish (hopefully not the last one) you have a back up drain that can handel all the flow from your return pump and avoid a flood.

As far as building the overflow itself, I went with a cheap and simple approach. Check out the pic. It's simply a PVC elbow that skims the water from the surface. It's smaller that bulkey boxes, the tank is drilled near the top rather than the very bottom (incase the bulkhead leaks, and the entire "overflow kit" cost less than $20.



That works, but you have very minimal surface skim and a lot of potential for anything to get into that drain.

Drilling and adding a weir or box is the ideal approach, anything else is a compromise.

[jon99]

An open elbow drain makes me afraid it's too easy for something to fall inside the pipes.

I was also worried about fish ending up in the sump, or a big chunk of bubble algae getting stuck in the pipe out of reach. I cut circular "screens" out of plastic gutter guard and placed them inside the elbow just where it begins to taper down. I clean them off every other month or so when algae begins to accumulate. So far no problems for 4+ years.

That works, but you have very minimal surface skim and a lot of potential for anything to get into that drain.

Drilling and adding a weir or box is the ideal approach, anything else is a compromise.

Skimming surface area of the glass-holes 700gph kit overflow box is 6.25". The elbows are 5" circumference each, X2 = 10" surface skimming area. Haven't seen any oil slicks in the frag tank yet :)

[Barro777]

http://glass-holes.com/Complete-Overflow-Kits_c3.htm I wouls suggest thhe 700gph kit.

Yes someone pointed me to that same website once before. I think I'm gonna do that. I mean, how hard can that be :) And it'll look cleaner without a siphon too.

Thank you folks, you are awesome!