Simple Physics Question.

[nfored]

View attachment 228988Please tell me why it flows great when capped and poorly when uncapped. see drawing and or read the post for details.


Ok here is my setup. I have a 24x16x12 tank with a 3/4 inch drain on the bottom. I hooked this drain up to a pvc pipe that runs under the tank and then comes up to the top of the tank. I have a T located where I want the water line, and that runs to the sump.

I have a strange problem If i don't cap the top of the T it flows poorly and will flood, if i cap it, then it flows like a beast and I can safely run my pump. However if its capped then the whole point of running it up the side of the tank to set the water level is pointless, as it will just siphon all the water out.

I came up with the solution of capping it siliconing a airline to it, and having the airline 1 inch under the waterline. this way when the water is above the airline the cap seals and flows like a champ, but when the water falls below the airline the cap unseals and stops the siphon from draining. I have no idea why I need a siphon when the tank has a drain. but this solution works 100% tested a couple times

 

[chesterthehero]

suction...

 

[johnptc]

it looks like uncapped the water level should be at the tee.......where is the water level uncapped ???

 

[nfored]

suction...

So because it can't pull air from the tube, its trying to suck the air out of the drain, causing the water to flow faster?

it looks like uncapped the water level should be at the tee.......where is the water level uncapped ???

uncapped the water will stop at the T with the pump off, but Its not safe to run uncapped as it hardly drains, the hight of the T doesn't seem to matter I have had the T at the top where it is now and almost at the bottom. It's working now with my modification I just don't understand the science behind it, and thats what I am trying to learn.

 

[chesterthehero]

So because it can't pull air from the tube, its trying to suck the air out of the drain, causing the water to flow faster?


mmhmm... or atleast thats my understanding of it.. i spent a good 5 hours building and rebuilding my overflow trying to figure different things out... im still not fully sure if i get it or not.. but either way it works so im not asking questions

 

[Knowdafish]

The way your overflow is setup capped is a glorified syphon. Capped with a hole in it is the same as if you drilled a hole in the top of a syphon. The ingestion of air interupts the syphon action and slows it down. An overflow from the SIDE of the tank would work better with the way you have it plumbed right now.

 

[nfored]

The way your overflow is setup capped is a glorified syphon. Capped with a hole in it is the same as if you drilled a hole in the top of a syphon. The ingestion of air interupts the syphon action and slows it down. An overflow from the SIDE of the tank would work better with the way you have it plumbed right now.

That would have been my choice, but these 2 tanks where 20 bucks each, with the hole in the bottom. The whole reason for the crazy plumbing is so I wont loose all the water in a power outage, and I want nothing visible inside the tanks, that’s why I didn’t use a stand pipe. I don’t have the drill bits to drill the side.

So what I am getting here is that the cap turns it into a siphon, If you see a better way please tell me I would love to have it just drain straight from the bottom, but like I said be for I don’t want to see anything but water and sand in this tank, so a stand pipe is our of the question.

I mean it works fine and I can actually change the water level by simply moving the airline up or down. My only fear is a turd or something gets stuck in the airline and seals it without my knowledge and the next power outage all the water drains out.

 

[nfored]

So because it can't pull air from the tube, its trying to suck the air out of the drain, causing the water to flow faster?


mmhmm... or atleast thats my understanding of it.. i spent a good 5 hours building and rebuilding my overflow trying to figure different things out... im still not fully sure if i get it or not.. but either way it works so im not asking questions

This is my second project, the first was the diy overflow from the stickies, between the two I have logged many of hours and pvc cement, also the other half gets pissy if you spill a whole can of purple primer on the flow and leave a permanent tint on the floor.

 

[johnptc]

maybe the way its drawn the pvc is too small allowing the pump to suck air...........

how many gph is the pump......

just for discussion if it was all 3 inch pvc it seems that once the tank level was equal to the tee it would stop flowing ???

 

[nfored]

RIO 3500 900GPH. I am not sure about the pvc being to small, I run a dual 1inch pvc overflow in my 55 Gallon, with a little gaint pew-800-pw 1000 gph. Note that is the GPH at 0ft head, I have not calculated the actull GPH for the head I am running on either pump.

I can't see what the pump has to do with the poor flow of the drian?