DIY overflow - tank either drains out, or overflows

mattybecks · Jan 31, 2020

Hi guys,

So I built my overflow and got the tap connected to the tank.
Everything works well, expect for the fact that the tank slowly drains out and then the overflow stops working once the water hits the level of the overflow. Then of course the overflow stops working and the tank overflows.

Excuse my ignorance, and this is my first time making one of these - but I thought the water would drain according to the flow rate of the incoming water?

It appears the water just drains over X amount of time and then cuts out. Increasing the flow rate just makes it overflow. Finding that thin line of exactly equal input Vs outflow doesn't seem like a good option. Even if you are a fraction of a millimeter off, this means over time your tank is almost guaranteed to overflow.

Trying to match the incoming water to the size of the pipes of the overflow doesn't seem like a good approach. It would require contanst adjustment everyday.

Am I missing something simple here?

mattybecks · Jan 31, 2020

Forgot to mention what I am going for is a "drip" water change system

mattybecks · Feb 1, 2020

mattybecks said:
Forgot to mention what I am going for is a "drip" water change system

Or maybe it's more a "flow through" system I am making instead of a drip system... Flow rate is faster than just a drip...

BIG-G · Feb 1, 2020

That looks like you’ve made it out of 1” pipe?
There is a limit to how fast that gravity will affect the flow.
So if your pump is more powerful than the amount of water that gravity can pull through the 1” pipe it will not start up fast enough and the pump will overflow the tank.
What GPH is your return pump?
Here is a chart that may help you match the flow better.

TheWolfman · Feb 1, 2020

I used a pvc overflow for 2 years for my drip and it never gave me an issue. I made it out of 1/2” pvc and it was able to keep up with my tap on water changes. A few suggestions here. I think the t is too high and needs to be slammed to the 90. I also would recommend changing the intake so it operates as a overflow box instead of the 180 that it has to go around. Lastly I don’t like that it chokes down from pvc to hose. If the water can’t escape properly then the overflow could turn into a full syphon. I attached a photo of my old overflow for reference. The ball valve was only used for setting up prime

mattybecks · Feb 2, 2020

BIG-G said:
That looks like you’ve made it out of 1” pipe?
There is a limit to how fast that gravity will affect the flow.
So if your pump is more powerful than the amount of water that gravity can pull through the 1” pipe it will not start up fast enough and the pump will overflow the tank.
What GPH is your return pump?
Here is a chart that may help you match the flow better.
View attachment 1403775

Thanks BIG G.
I don't actually have a pump. The water was coming straight from the faucet into the tank. So I really don't know what the gph is. All I do is open and close the tap to increase or decrease water flow to the tank.

mattybecks · Feb 2, 2020

TheWolfman said:
I used a pvc overflow for 2 years for my drip and it never gave me an issue. I made it out of 1/2” pvc and it was able to keep up with my tap on water changes. A few suggestions here. I think the t is too high and needs to be slammed to the 90. I also would recommend changing the intake so it operates as a overflow box instead of the 180 that it has to go around. Lastly I don’t like that it chokes down from pvc to hose. If the water can’t escape properly then the overflow could turn into a full syphon. I attached a photo of my old overflow for reference. The ball valve was only used for setting up prime View attachment 1403776

Thank you TheWolfman!
Really insightful and I am starting to see my mistakes.
The T piece I should lower a bit so it looks like yours, with elbow touching the T piece.
May I ask how you set up the overflow box on your system?
Mine was running as a full siphon. So Ianded up removing the whole PVC overflow I built, and just added a tube from tank into the drain, with a open/closed valve.
Now if I need to do a water change its as simple as turning the valve and the tank drains pretty quickly.
Filling up from the faucet under the sink is also just a simple "turn on the tap" and the tank fills up. Takes 15 - 20 min in total for a drain and fill. I always like to do an 80% water change. So although I haven't succeeded with my drip/flow through tank system. I have made my water changes much easier and much faster. Only have to turn taps on and off.