Water flow experts , why is the water lvl in 2nd gravity sump lower than 1st sump?

Mike01z · 08-23-2007, 04:24 PM

Here is a diagram of the layout

the 1st sump has a 1 inch bulkhead that gets expands to a 1.5 inch fitting where it enters the UV and on the backside of the UV it exits at 1.5 inches and splits into 2 1 inch pvc pipes that both go to my 2nd gravity fed sump.

When the water is off the water levels in both tanks are equal, when I turn the pump on the water lvl in the 2nd sump is a few inches lower than the 1st sump but the water lvl does not fluctuate nor does the 2nd sump ever act as if its gonna run dry as if there was a restriction of not enough flow between sump 1 and 2.

The setup is working I'm just curious as to why its this way, I figured the water lvl would be at the same heigh in both sumps whether on or off.

The picutre illistrates how it is with the return pump off, with the return pump on the water lvl in the 1st sump stays the same and the one in the 2nd sump is a few inches lower than the first.

tiburon · 08-23-2007, 04:29 PM

maybe because the line after the UV sterilizer (or something in that chain) feeding sump#2 is a little restrictive? that and you're pulling water out of the end of the line back to the tank so it's always fighting to fill sump#2... just a guess.

Wiskey · 08-23-2007, 04:33 PM

It's probably because you have to force the water through all that plumbing,.. the larger the differental between the 2 the larger the force behind the water to move, when they are equal there is no force at all.

Whiskey

Hop · 08-23-2007, 04:42 PM

The water height when running in the second sump should be determined by the baffles or by an ATO depending upon how it's ran. Pics of the actual set up could help me figure out why... But it's working so don't mess with it

Mike01z · 08-23-2007, 06:20 PM

ATO does govern the 2nd sump and thats the only place I can control the water lvl, the 1st sump never changes, weird.

If it was water pressure issue with the inlet not letting in enough water I'd think that the water lvl would flucuate in the 2nd sump if not run dry. Also the reason I say this is because I stopped the auto top off for about 12 hrs or so just to watch the water evap and the water lvl dropped in the 2nd sump yet still stayed the same in the 1st sump, I would think a difference of pressures here would cause a variance at least minimally in the 1st sump.

hmmmmmmmmmmmmmmmmmmmmmmmmmm

but then my concious tells me that it is water pressure. hmmmmmmmmmmmm

bguile · 08-23-2007, 07:03 PM

Here's my theory on it, I'm no expert but I think I might be close. There's nothing wrong with your setup, it's because of the latency in the overflow (for a lack of better terms).

In an off state, everything is level. When you turn your return pump on, it has to pump enough water up to your tank to fill the pipes up to the tank AND put enough water in the tank to "push" the water over the overflow. If you turn everything off, water will continue to go over the overflow for a few seconds because it's still in motion and higher than the overflow. Once it can't get over the overflow and all the water has drained back from the piping system (I'm going to assume that you have a vacuum break in the return plumbing), everything evens out.

So if anything, that's where the water is going. And since your pump is always running the water level can't catch up.

digitalis · 08-23-2007, 07:44 PM

It looks to me as if your UV Sterilizer isn't allowing enough flow through it. the first sump is always the same because the same flow from the tank is always overflowing into the first sump. Because there is a set volume of flow though the sterilizer, the same amount is always in the 1st sump. When water evaporates, the same flow is maintained through the sterilizer, and to the tank, so the water goes down in the 2nd sump. If you ran larger lines to the sterilizer or made the line more curved instead of elbows, it would probably flow faster, and both sumps would be closer to even. The first would have less water, and the 2nd would have more water. You may be at the limit of flow on your system. If you got a larger pump, you might just empty your second sump while the first was still trying to drain into it.
I hope that makes sense. That's what I think it sounds like.