DIY RUGF -- Need a lesson in water flow dynamics

[amhodge]

I've finished the most time consuming part of the work for my DIY RUGF; now I just need to arrange the tubing and I have some questions.

I've used the model of this RUGF in deciding the basic design:

http://www.thekrib.com/Filters/rugf.gif

One exception I'm making is that I'm not going to skim from the top as illustrated in the model. I'm also going to try to prevent getting too much debris under the tray by putting a sponge in the intake, assuming that does not hurt the water flow too much.

What I'd like to know is:

1) What puts the R in the RUGF? What is it about this design that causes the water to flow in the reverse rather than flowing out of the "in"take? I will be using an airstone rather than a powerhead, as in the model.

And on a related note:

2) What lengths of tube will ensure the best flow? Is it best to have the tube sticking up from the grid go all the way to the top, followed by the 90 deg. bend & T, then have the second tube stick all the way back down to the bottom, or can I shorten the second tube and perhaps get better pull in the process? What's the most efficient design (besides just getting a powerhead)?

And regarding substrate:

3) I have read that UGFs require 2-3" of substrate. Is that a minimum range (at least 2-3" of substrate), or is that a minimum/maximum range (no less than 2" and no more than 3" of substrate)?

4) I have also read that UGFs require that you keep your gravel level to allow even flow through it, but I want to slope downward toward the front of the tank. Can I put a sloping layer of larger gravel down, then cover that with a layer of Flourite that is thicker toward the front, therefore having a higher level of gravel in the back, but with more space available for water to flow through, thus evening out the flow? Alright, that's a confusing question, so here's a terrible representation of what I mean, where the O's are the larger gravel and the o's are the flourite.

oooooooooo
OOOOOoooooooooooooo
OOOOOOOOOOooooooooooooooooooo
OOOOOOOOOOOOOOOoooooooooooooooooooo
OOOOOOOOOOOOOOOOOOOOooooooooooooooo
OOOOOOOOOOOOOOOOOOOOOOOOOOooooooooo


Finally, if the above is feasible:

5) Is there any material I can layer between the larger gravel and the flourite that will keep them from getting mixed up when I vacuum? The same door screening I used for my filter tray perhaps?

Thanks!! :read:

 

[isuchopper]

I guess I can help with a couple of your questions.

1. The R, as I have read, is for reverse. The general idea with this design is that the air/water mixture in the middle tube (the one without arrows in your diagram) is less dense than pure water. This being the case, there is a pressure difference between the pressure of the water water in your tank at any given depth and the pressure of the air/water mixture in your middle tube. This difference in pressure is what causes the air/water mixture to rise towards the surface of the tank- up the middle tube. This pressure difference also acts on the water in your first tube- on the right hand side of your diagram. Since the water in this tube is at 'tank' pressure, it not only pushes the air water mixture up the middle tube but also flows along right behind (or else we would have a vacuum forming in the tube).

When the water gets to the top of the middle tube, it's best course is now down the left-most tube and into your UGF.

Does that make sense or did I mess stuff up?

2. Regarding the length of the tubes. Fluid flowing through pipes actually meets resistance as the fluid tries to run along the (relatively) rough inside face of the pipe. This resistance increases with speed and is the reason that your faucet doesn't shoot water across your kitchen unless you restrict the flow- for water to run that fast through the pipes in your house, it would have to have a lot of pressure behind it. Since we would like the incoming water to meet as little resistance as possible, we would like the first (right-most pipe) as short as possible. This might make surface skimming a little tough, though.

The middle pipe is a different story. Going back to that pressure difference and that fact that it is the force driving the water flow, we want it as high as possible. Therefore, we want that middle tube as long as possible. Of course, you'll could run into issues with the pressure loss (resistance) from the pipe being too long, but I doubt it in this case. The big issue with this system will likely be the diameter of the pipes. Larger diameter pipes offer less resistance, so your water can flow more freely.

Given that, I would grab a couple different tubes and see which seems best with the air pump and stone that you're running.

4. Seems to be correct logic. I can't tell you what the relative heights need to be, but you see similar techniques used in HVAC when they neck down to smaller ducts to force more air to exit out the vents further upstream.

5. Not an expert, but that sounds fine to me.

Hope this helps.

It's pretty late so can any other ME/CE/CivE/AE's out there look over the above and let me know if I sound like an idiot?

Thanks.

 

[Rbishop]

At best, that design is extremely a low flow application. You are more likely just going to get flow thru the "U". The water will come down the inlet and up the air tube and with sufficeint air, it will pass right out the top with the air.

If you cut the air down to the point that doesn't happen, you will just be agitating the water in the center tube.

There isn't any head being generated to get the water down the third tube. Any head pressure on the water in the tube is the same as at the bottom of the tube.

 

[amhodge]

Thanks for the responses. I'm attaching a picture so you can see how my project differs from the model I'm going by.

isuchopper, you're more articulate than you give yourself credit for as that all makes perfect sense to me. Especially your point on resistance, and there I can see a major problem with my design. At both of the U's I used elbows that abruptly cut the pipe diameter from 3/4" to 1/2" which is probably hurting the flow, especially at that critical second bend where I need to somehow direct the pressure toward the final tube. I think I need to find a way to create the bends while keeping a consistent 3/4" course. Perhaps using rings that will wrap around the outside of the PVC and join the 3/4" lengths directly together. Another trip to the hardware store.

And Bob, you're right, this has been extremely low flow. I tested it last night with food coloring and the water is just seeping through it and getting slowly dispersed through about half of the tray. As to the agitation, you can see that I've attached an extension to the top of the T. Inside the bottom of that extension, I've wrapped a bit of filter material around the airline in the hopes that it would allow air to escape while blocking water. This doesn't seem to be working. I think the water is mostly just being agitated at the T, as you suggested, and that the pressure is not being redirected toward the second bend. I need a system that will allow air to readily escape while not absorbing the water, but with what material?

 

[MrCracker2u]

Your putting way to much work into this IMO. just use reverse flow p/hs on top of the stand pipes. put the sponge filter on the normal output of the ph if you want low flow use small power heads.

 

[amhodge]

Your putting way to much work into this IMO. just use reverse flow p/hs on top of the stand pipes. put the sponge filter on the normal output of the ph if you want low flow use small power heads.

Too much work to be practical, yes, but I'm not trying to be practical. I'm trying to build my first DIY aquarium project and figuring out the optimal flow that can be achieved with an air pump (that I picked up for $3 and am trying to dream up a use for) is part of the experience and part of the fun.

I've figured all along that in the end I'll probably get a powerhead when I put together a similar rig for my larger tank.

 

[Soulcoffr]

Too much work to be practical, yes, but I'm not trying to be practical.

I was wondering why you just didn't use a reversed powerhead. It's all becoming clear now. Good luck!

 

[amhodge]

Ha! I figured it out and now I'm laughing at myself. Basically, I just moved the T over to the pipe that sticks up from the tray. Then I fed the airline into the top of the T, as before, and out the horizontal part of the T, down through an elbow and into the next tube over. Now the water from the intake is being led by the air bubbles through the elbow, where before it had little incentive to make that turn. The pipes are now sucking the water through at a fast enough rate that I can see the food coloring come out under the tray almost as soon at it will feed into the intake.

I'll post a pic or graphic later if this is confusing.

 

[Que]

Cool... it'd be nice if you can figure out your flow rate.

Q

I've been toying around with ideas for cheap simple filters that actually work and don't need much power but I haven't had any time to experiment with it.

 

[amhodge]

Cool... it'd be nice if you can figure out your flow rate.

I was thinking the same but I don't imagine I could get an accurate idea of velocity with such a short distance of travel. So, figure the slowest powerhead rate available and cut that by half