Overflow issue

I've been working on the overflow for my project, but I've been having a problem with the amount of flow.

I have the overflow set up on a test rig to figure out the max flow I can put through it. I came up with the whopping number.....60 gph.

The method:

The inner box was inside a pot, the outer had the outlet over the sink. I found a spot where the sink (with a extension hose) was only putting out as much as the overflow can handle, by finding a flow rate on the sink that kept the water level steady in the pot. Then I put the hose in a gallon jug and let it run for 1 minute, and got approximately a gallon of water.

Does that seem wrong to anyone? Should the flow rate be faster with a 5/8" U Tube configuration with 2 90 degree elbows?

I put in a flexible tube, 5/8" ID, as the U Tube (with no elbows), and got 90GPH as the max. Then, I used a 3/4" tube, and ended up with more flow than the sink could put out to measure, but not by a large amount. I could flood it by adding a piece of airline sized tubing and siphoning some water from another pot. This still seems low to me; anyone else have an opinion?

 

It will have a lot to do with the amount of pressure (amount of water pushing behind it) and the height it has to drop. Here's a useful chart of flow amounts possible with different size pipes GPM/GPH Flow based on PVC Pipe Size, ie, How much water can flow through Sch 40 Pvc Pipe Size 1/2" 3/4" 1" 1.5" 2" 2.5" 3" 4" 6"

TJ

 

It's gravity fed. It's an inch of water over the inner box. There's no "height it has to drop"; this is an overflow box, and I'm worried about the U Tube, not the drain pipe. It's a flexible vinyl tube, not PVC.

Even so, the number on that site for 1/2" PVC that's gravity fed is 7 GPM, which is 7x what I'm getting with the 5/8" U Tube with the elbows.

 

I see what your saying now. Have you tried a much larger U-tube diameter? Like 1 1/4" or something? Where there's not much distance for the water to drop it's not able to gain enough speed to come close to the pressure needed (or in this case vacum) to get near the max flow rate of the pipe. I've never used a U-tube style overflow so I'm being hypothetical here.

TJ

 

Bubbles are hardly being pulled out of the tube with the 3/4" ID tubing; I wouldn't want to go bigger because at this flow rate with this pipe, I'm already on the brink of a big failure because of bubble buildup.

 

Hmmm, maybe that's the problem. From what I have read, you don't want any air pockets in the top of the tube. Drill a hole at the highest point of the top of the U so a piece of airline tubing will fit snuggly and use an auqalifter pump or just your mouth to get the air pocket out and start the siphon. Just for the sake of experimenting

TJ

 

I had been starting it by putting airline tube into it then sucking out the air. There's no air when I start the flow.

I'm talking about when a bubble gets caught, like if I put some airline tubing near the intake and make a small one for the sake of testing. It's definitely not flowing at the rate I want, because it can't keep from having very small bubbles get stuck.

The 5/8" ID tubing has no problem with bubbles getting caught, but it won't give enough flow.

 

The bubbles are building up because there is not enough flow thru the U-tube.
A 1" U-tube will handle up to 900gph without a problem, In this case I believe there is a flaw in your test.
The water on the output side of the U-tube must drain away at an equal or greater rate so the syphon will continue to draw water from the tank side, otherwise it will build up a back pressure and slow things down.

 

I'm using 3/4" ID vinyl tubing for the bigger tube. I just realized that's different from the typical U Tubes because they're usually a solid piece of acrylic.

The outer box isn't holding any water past the height of the "baffle" (to keep from having a siphon break); it's draining away really fast. Here's a quick diagram of the outer box while the sink is running full speed:


It's like that, where there's nothing building up in the drain compartment at all, and water is flowing over that "baffle" in literally maybe a 1/8" layer, which is why I don't think it's the outer box construction that's the problem.

 

I just tried it with a 1/2" vinyl tubing and got around 120 gph. When I tried it with 3/4" the gallon pot was full before I could even count it. Do you have a kink in the hose? Is the outside box water level lower than the "tank" (or pot) water level?

TJ