what is the max gravity GPH through various ID pipes/tubes

[Marshall]

I'm trying to calculate the maximum gravity flow through various sizes of tubing. For example, 3/8" ID tubing... what could I expect to flow through that if I had such a line on the side of my sump (not the bottom) and the water level was a few inches above it? It is "known" that a 1" drain flows ~600gph... how does one figure that out? And how can I figure it out for 3/8", 1/2", etc? Thanks!!

[Marshall]

Well to partially answer my own question, you can screw around with the RC calculator until your diameter pipe shows up. I don't know how accurate that calculator is for smaller pipes though.

[Alfalfameister]

I *think* the RC calculator is useful for maximum (gravity) flow a certain pipe diameter can handle. But I don't think it takes into account noise (gurgling/splashing/etc)... so, the bigger the better.

[SuperDodge]

OK......a 1" drain is not KNOWN to flow 600 gph. In order to solve this problem you need to understand it. If your tank were a foot higher it would flow more through a 1" drain than if it were lower. If you had less 1" tubing, it would flow more than if you had to make a longer run of 1" tubing. Believe me. You can't just say that a tubing size will flow some amount.

The pressure at the waterlevel in your overflow is 14.7 psia or 0 psig. The pressure at the terminating point of drain piping is 14.7 psia (0 psig) if it is above the sump water level. If you run your drain line under the water in your sump, then the pressure at the termination of you drain pipe is the hydrostatic pressure where the drain ends. The amount of head available is the height difference between the water level in your overflow and the terminating point of your drain line. Because of these fixed pressures at the inlet and outlet of your drain, whatever line size you chose for the drain will flow just enough water that the friction losses (in feet) will be exactly equal to the head available for your setup.

TO CALCULATE THE HEAD AVAILABLE IN YOUR SETUP:
If your drain lines terminate above the sump water level:
Calculate the height difference between the level of water in your overflow and the terminating point of your drain.

If your drain lines terminate under water in your sump:
THe height difference between the water level in your overflows and the water level in your sump is your head available (any extra distance the pipe extends below the water surface is offset by the hydrostatic force it must overcome).

Now you have to do the balancing act. You have to find the flowrate where your pressure loss is equal to the head available you calculated above.

There will be a pressure loss through your standpipe. If you have a durso, you will have to consider the pressure drop through two elbows and the straight run of pipe from the bottom of the elbows to the bottom of the tank. You will also have to consider the loss through TWO sharp edged entrances. This will account for the entrance into the standpipe and through the bulkhead. The pressure loss in your turbing from there down is purely straight run loss (assuming you haven't been the tubing all around). There are many many calculators on the web to calculate friction losses through the straight runs. The fittings are the hard part, and while I have reference books with lists of loss coefficients, the equations you would need to calculate using them are past the scope of this discussion.

To get an idea of the loss in the straight runs in your system you could use the table shown at http://www.watergarden.com/catalog/_...friction.html; however, I stress that you not look at the lower table that shows losses for fittings because they are not calculated numbers they are just rules of thumb used in high pressure pump applications. Since this is not a pump application, they do not apply.

If you are looking for some magic flowrate and want to know what size tubing you should use, just post up details about your system and I will be glad to use my reference materials and tell you what size tubing you need to use in order to achieve.

Please please please, just don't ever think that it is a set thing that a 1" tube flows 600 gph under gravity.

-RL

[rdmpe]

Another thing -

If you check out this thread
http://archive.reefcentral.com/forum...hreadid=344892
If you have an extra hole for the "emergency" drain, then this drain method will allow the "main" drain to develop a full siphon. I think this will allow a given diameter/pipe system to drain more water than a system that has air entering the drain AND it will be silent. I'm no hydraulics expert though so SuperDodge I'd love to hear your opinion on that...

Be sure to go to the "last page" and you'll find that several people have been using this setup for a long time with great results.

I plan to do this when I finally get my 180g plumbed...

[SuperDodge]

Guys, I wrote this reply and like 4 in the morning and I realized that I never prefaced it by saying the situation I described the pressures in was the case where the drains were flowing the maximum they could handle. Be sure and keep that in mind. If you're flowing any less than the maximum then you actually have a discharge pressure.

Just wanted to clear that up now that I'm rereading what I wrote.

[Rivalpc]

Problem is I understood all of that, even after 12 years of not dealing with neumatic or hydrolic fluidic calculations... and trust me when i say its a lot of calcs with many variables.

[Stile2]

I'm glad someone understood it

[SuperDodge]

It's not too many calculations. You could do this entire calculation on the front side of a piece of engineering paper.
(Insert cheesy, I promise I'm not a nerd face here)

[Marshall]

The reason I asked this question was because I plumbed in a 1/2" hose barb connected to my plumbing that can be switched to drain through 3/8" OD tubing. It could not keep up even with like 20 feet of 1" pipe to hold the excess during a large water change. I upgraded to 1/2" OD tubing (the largest push-in fitting compatible tubing you can buy easily). I did a water change yesterday and I thought it was going great because there was no backup upstairs but of course I also had my skimmer hooked up to that drain and the water shot right up through it. DOH!!!! I will fix that shortly and hopefully I can flow the 1/2" siphon through the 3/8" ID (1/2" OD) tubing without a hitch. There is some 15 foot of vertical head between the two.

Thanks for everyone's responses... one last question: where does the RC calculator come from? Are they making inappropriate assumptiongs? It seems like most people I've talked to say 1" BH will flow 600gph... where does that come from? Also, most overflow boxes are rated for 600, 1200, etc gph. Where do those #s come from?

Cheers,
Marshall