Size pump question

[mfinn]

How do I try to explain this. No, your right it doesn't stop, per say, but the overflow will drop 700gph, so its much faster than your 400gph, so, there is a lip in the tank that fills with water, the weir, then flows it into the back chamber, its not being utilized correctly, just trickling in. If your just going with a 400gph theres no need to go with a 700gph overflow, absolutely no reason.
It takes time for your tank to fill with 400gph if its being drained a rate of 700gph, that make any more sense?

My main reason for going with larger overflows than the return pump have several reasons.
One is noise. slower flow is much quieter. Another is if you overflow is near capacity, then any little thing can plug it and you get a flood. Another is, if you decide to change pumps to a stronger one, you have some wiggle room.
Smaller return pump is less power, plus generally cheaper pump. The last is such a small part for me, but not others.
Slower flow means less chance of micro bubbles in the display.

The water will flow just fine

Your statement that it's not being utilized correctly is saying that if we don't do it your way, then we are not doing it right.

I know many who do like to get more flow from their return pumps and that's fine, I have learned from many systems that I have setup, that slower works for me.

 

[nervousmonkey]

How do I try to explain this. No, your right it doesn't stop, per say, but the overflow will drop 700gph, so its much faster than your 400gph, so, there is a lip in the tank that fills with water, the weir, then flows it into the back chamber, its not being utilized correctly, just trickling in. If your just going with a 400gph theres no need to go with a 700gph overflow, absolutely no reason.
It takes time for your tank to fill with 400gph if its being drained a rate of 700gph, that make any more sense?

The overflow can only drain as quickly as the return is adding water back. There is an equilibrium there, unless the return is higher than the overflow. So the overflow will drain at 400 gph in this example. I know it has the capacity to drain the tank at 700 gph, but it can't physically drain 700 gph from a tank that only has 400 gph going into it. Another way to think about it is if the OP put a ball valve on one drain line to keep the overflow full and let a second drain line pick up the extra. That would be an Herbie style overflow, draining at the exact same rate that the return pump was providing.

 

[NanaReefer]

How do I try to explain this. No, your right it doesn't stop, per say, but the overflow will drop 700gph, so its much faster than your 400gph, so, there is a lip in the tank that fills with water, the weir, then flows it into the back chamber, its not being utilized correctly, just trickling in. If your just going with a 400gph theres no need to go with a 700gph overflow, absolutely no reason.
It takes time for your tank to fill with 400gph if its being drained a rate of 700gph, that make any more sense?

You're looking at this wrong. It's rated to handle "up to" 700gph. Meaning anything under is fine. Just don't use a pump rated higher.

 

[Reefing Madness]

Im, not looking at it wrong. I've run an overflow, it make a bit of a kinda gurgle noise when it not completely filled, if it keeps waiting for water its not quiet, imo.
But thats just the way I see it. I've raised it, lowered, then got a pump rated for what the overflow was rated at, and BINGO, no more gurgle, no more noise. jmo.

 

[Reefing Madness]

Oh forgot one thing to mention.
I still don't see the point of getting an overflow rated at 700gph if your only gonna run a 400gph. Why not just get a 400gph then run a 200gph return, oops, then you'd only need a 200gph overflow and run a 50gph return.......See my point with this one?

 

[nervousmonkey]

sorry for the double post...

 

[nervousmonkey]

Im, not looking at it wrong. I've run an overflow, it make a bit of a kinda gurgle noise when it not completely filled, if it keeps waiting for water its not quiet, imo.
But thats just the way I see it. I've raised it, lowered, then got a pump rated for what the overflow was rated at, and BINGO, no more gurgle, no more noise. jmo.

OK, I gotcha now RM. Yeah, overflows are horribly noisy unless you tune them with ball valves to drain close to the rate of your return pump. Yeah, same has happened to me too. It's from the overflow filling up, then a suction gets created, then drains the whole overflow box and it's noisy as ****. So, point to the OP, if you don't get a pump rated for close to 700 gph, then you will hear noise. That is if you use a Durso style drainpipe.
Herbie style: If you set up two drain pipes and use a ball valve on one line to keep it running at full suction (doesn't matter the rate of suction, be it 300 gph or 600 gph), and keep the second drain to pick up the extra, you will not hear much gurgling/noise. Or, my preference is a beananimal overflow, but I don't think you can set up a beananimal overflow with a glassholes box...
To the OP, just do an Herbie drain to keep it quiet, so you have an overflow that matches what your return pump is providing as well as providing some emergency help with one drain that isn't draining much (make sure the second is draining less than 25% of the water flow, otherwise you'll hear the gurgling in the drain pipe).
Yeah, @Reefing Madness is right. You'll hear noise if the two don't match closely. I see where you were going man...

 

[nervousmonkey]

Oh forgot one thing to mention.
I still don't see the point of getting an overflow rated at 700gph if your only gonna run a 400gph. Why not just get a 400gph then run a 200gph return, oops, then you'd only need a 200gph overflow and run a 50gph return.......See my point with this one?

I see your point, it's just reduction until you get to zero. The point of having an overflow rated higher than the return is providing is purely protection, so if one drain gets clogged, you have a second as emergency, or a third... If you only have one drain pipe from the overflow, there should be a close match to the return if you want to avoid a noisy overflow. And then some insurance with an alarm if water overflows the DT...

 

[mfinn]

Oh forgot one thing to mention.
I still don't see the point of getting an overflow rated at 700gph if your only gonna run a 400gph. Why not just get a 400gph then run a 200gph return, oops, then you'd only need a 200gph overflow and run a 50gph return.......See my point with this one?

Like I said several times, I've done tank set ups with slower flow for a couple decades. Nothing has gone wrong.
I will continue to do it this way.

You do it your way, I will do it my way.

 

[NanaReefer]

The glass holes overflow box I got came with an insert. It sits inside the box resting on top of the bulkheads. Over that is a piece of large holed mesh material. Also there is a hole drilled into the bulkhead elbow where a piece of tubing is inserted. All together my overflow is completely silent.

Actually I owe this knowledge to @mfinn. My tanks plumbing has been running flawlessly for almost 2yrs.

 

[mcarroll]

Whats the point of getting a 700gph overflow if your just going to put 400gph through it? And If you've ever run a starving overflow with a slower pump, you'd understand, like fill stop, fill stop, fill stop. That makes no sense.

There can be lots of reasons to run a pump "slower" than your drain, but less noise and fewer bubbles being generated are two good ones. Arguably, there hasn't been a good reason to run "a lot" of flow through your return pump since the dawn of the propellor pump.

Generally, when a drain is run close to its design spec you get noise and bubbles issues, then you get to play games trying to silence the drain and eliminates the bubbles...that you created. Bye-bye plumbing contraption in my drain box! Bye-bye useless space-eating baffles in the sump!

Up to its limit, a gravity drain works exactly as fast as the pump that's returning water - always. Unless you stop and start your pump, there's no reason your drain should stop and start.