skimmer bar overflow questions, please help

[nolken]

Originally Posted by RocketEngineer

Scientific answer:
Flow rate is determined by the height drop between the inlet and outlet. In our case, this height drop is applied along a horizontal pipe and must therefore be provided by the water level upstream rising in relation to the outlet height. The problem with the slotted horizontal pipe is that you reach a point along the pipe where the outlets are so far from the inlet edge that the water level necessary to push water towards the outlet equals the height of the inlet. At this point, the water level in the horizontal pipe IS THE SAME AS THE TANK. No surface skimming can be achieved because water has totally filled that portion of the overflow pipe.

Put another way, in order to achieve surface skimming along the entire length of the horizontal pipe, the horizontal pipes must be sufficiently short as to keep the water level in the horizontal pipe below the lip of the slot in the pipe. In order to achieve high flow rates, multiple outlets would be necessary with additional outlets needed for each increase in flow.

I considered this as mentioned in a previous post, thats what was I thought I had solved with the sloped bottom

Originally Posted by RocketEngineer

uncleof6 and I aren't trying to pull your leg. We really do understand the physics involved and are trying to help. In my case, I built a system like this and learned first hand IT DOESN'T WORK. One of the reasons my 75g has algae problems is a lack of flow to the sump which limited how much water the skimmer and refugium could process. My 125g will fix that problem.

I know this. I appreciate uncleof6 and your experience in this subject and your input. The only think that is bugging me is it seems to be going against what i learned in engineering physics and fluid mechanics. As engineers (i'm assuming you are) we know that just because something works theoretically and on paper that doesn't mean it works when implemented. I'm not saying it will work, and i'm not saying you are wrong. I'm just saying i don't see on paper why it doesn't.

And from what i remember isn't the flow rate determined by the pressure by the water? In this case the gravitational force the water is supplying on the drain plus the atmospheric pressure?

I'm putting way too much time and thought into this.

[RocketEngineer]

Originally Posted by nolken

And from what i remember isn't the flow rate determined by the pressure by the water? In this case the gravitational force the water is supplying on the drain plus the atmospheric pressure?

Flow rate is determined by friction loses and head vs differential pressure. When you have a pump, overcoming fiction loses and head is done by the pressure the pump generates. In an impeller pump (common hobby pump) this pressure is created by the impeller throwing the incoming water against the outer housing using centripetal force.

In this case the pressure is only being supplied by the height difference in the water level (gravity). This means that there has to be SOME height difference between where the water comes in and where it exits or nothing flows. Now, if the flow rate were low enough, the water in the pipe will find level such that the end of the level section of the pipe is beyond the edge of the elbow and the system would drain as fast as the water enters. Unfortunately, this scenario is very low flow so we try to push the system harder. By increasing the flow rate above the purely level scenario, you create a pile up within the horizontal pipe as more water enters than leaves. The pileup in turn increases the height difference which causes more water to leave due to the increase in pressure at the exit eventually reaching equilibrium. The Achilles heal with the system is if you keep increasing the flow rate, eventually you get to where the height difference is equal to the inner diameter of the pipe in which case increasing the flow beyond that point will only decrease the portion of the slot that's pulling water from the surface.

Originally Posted by nolken

I'm putting way too much time and thought into this.

Yup. Just take our advice and go with a BeanAnimal overflow and you won't regret it.

RocketEngineer

[nolken]

Very well said. Makes much more sense. I'm EE & CpE so never got too deep into fluid mechanics. Thank you for your thorough explanation sir. to you as well uncleof6.

[cheezischrist]

thank you all, but another question. if i was to go to 1.5" pipe or 2" on the outside for the drain lines, wouldnt that defeat the pile up and make it drain wit less friction and increase flow?

[uncleof6]

Originally Posted by cheezischrist

thank you all, but another question. if i was to go to 1.5" pipe or 2" on the outside for the drain lines, wouldnt that defeat the pile up and make it drain wit less friction and increase flow?

Simple answer: NO! please do yourself a favor--this design does not work as advertised unless the flow rate is very low. Only so many ways to say this: Build something that does work.

[Joe Blowfish]

I thought maybe I'd chime in here...

Despite the fluid dynamics disputes, the skimmer bar does work. I have the proof in my basement. The physics here is really quite simple - you have orifices on the back of the tank that must be large enough to drain the return input and overcome the friction loss of directing the water through the skimmer bar slot. Yes, air enters the piping, and yes, it reduces the water volume in the piping, slightly. There's no reason why this design can't work for higher flow - but it would mean increasing the bulkhead size and skimmer bar diameter...and the slot area would have to increase proportionately (either by length or width). Based on my experiments, 1.5" PVC could drain 600-700 gph with the same safety factor I'm using (which is overkill).

A coast-to-coast or beananimal overflow has it's advantages over this skimmer bar (mainly that they're perfectly quiet), but the noise coming from my water flow is less than my return pump's hum. And there are some nice advantages of going the skimmer bar route - it's much cheaper, smaller and simpler ...and easier to keep clean. I'm not arguing that one approach is better than the other (in-fact I love the beanaminal design), just that both work and both have pros & cons.

There are a couple posts about an MD5 (500gph) and a RIO1700 (642gph) pump having to be dialed back...I'd really like to see those designs to understand what is happening. As stated in my video, I'm running an ECO633 full-out and not only does it drain easily, I can reduce the skimmer slot down to ~25% of it's length and it still drains. This should address the flood concerns raised - my safety factor is ~3.6 (more than double what the FAA allows).

I'd be happy to answer any questions and assist those who are having trouble getting their designs to work as they wish. It did take me two tries to get the slot right, but I actually reduced the size on the second version.

- youtube guy

[uncleof6]

Originally Posted by Joe Blowfish

I thought maybe I'd chime in here...

Despite the fluid dynamics disputes, the skimmer bar does work. I have the proof in my basement. The physics here is really quite simple - you have orifices on the back of the tank that must be large enough to drain the return input and overcome the friction loss of directing the water through the skimmer bar slot. Yes, air enters the piping, and yes, it reduces the water volume in the piping, slightly. There's no reason why this design can't work for higher flow - but it would mean increasing the bulkhead size and skimmer bar diameter...and the slot area would have to increase proportionately (either by length or width). Based on my experiments, 1.5" PVC could drain 600-700 gph with the same safety factor I'm using (which is overkill).

A coast-to-coast or beananimal overflow has it's advantages over this skimmer bar (mainly that they're perfectly quiet), but the noise coming from my water flow is less than my return pump's hum. And there are some nice advantages of going the skimmer bar route - it's much cheaper, smaller and simpler ...and easier to keep clean. I'm not arguing that one approach is better than the other (in-fact I love the beanaminal design), just that both work and both have pros & cons.

There are a couple posts about an MD5 (500gph) and a RIO1700 (642gph) pump having to be dialed back...I'd really like to see those designs to understand what is happening. As stated in my video, I'm running an ECO633 full-out and not only does it drain easily, I can reduce the skimmer slot down to ~25% of it's length and it still drains. This should address the flood concerns raised - my safety factor is ~3.6 (more than double what the FAA allows).

I'd be happy to answer any questions and assist those who are having trouble getting their designs to work as they wish. It did take me two tries to get the slot right, but I actually reduced the size on the second version.

- youtube guy

But your experimental data is incomplete. What is needed is the real world flow rate. It is nowhere near 600gph, let alone 700 gph, because, according to the advertising, the the ECO633 pump starts at 633 gph. By the time the plumbing is added to the static head (friction loss) you will be lucky to be above 200 gph. Nor have you stated that you are not running other equipment with the pump, which most do. The claim that it can flow 600 - 700 gph, is unfounded.

According to the flow curve, @ 0' the pump does 527 gph! At around 4 ft (average static vertical lift) that is down to around ~300 gph. At 6.5' average total head loss (with friction loss added in) it is down to 131 gph. To be fair, it may be 5' so say the average real world flow rate will be between 131 and 263 gph--assuming the output is not split to other equipment.

There is simply NO proof of concept here. Sorry. Those of us that understand the physics of this device, and have actually fought with them, say they are useless, for anything but very low flow--and at that they work very well.

[cheezischrist]

i might be under the wrong impression, but dont you want low flow through your sump? more contact time for the skimmer to process water, more contact time for macro algae to handle nutrient export, more contact time for the heater to warm the water? a more stable enviroment for pods to be able to function and grow, not be swept out immediately?. my main concern was for pump sizing, not flow in my display, wavemakers will handle that.

[uncleof6]

Originally Posted by cheezischrist

i might be under the wrong impression, but dont you want low flow through your sump? more contact time for the skimmer to process water, more contact time for macro algae to handle nutrient export, more contact time for the heater to warm the water? a more stable environment for pods to be able to function and grow, not be swept out immediately?. my main concern was for pump sizing, not flow in my display, wavemakers will handle that.

Wrong impression on all of the above. The above is pretty much an anthem of mythinformation, put forth by well intentioned folks, but the information has no basis in real science--it is more reaching for excuses to get that smaller pump....

None of the above are in any way connected to the flow rate through the sump, and wave-makers (another gadget I see no value in whatever)--power heads yes make water movement, but they do not make "flow"--in the context of this discussion, they are different things.

Contact time is only a consideration INSIDE the skimmer. It does not matter 2 cents anywhere else. Skimmer performance is based on flow through the skimmer, not right past it, and even at 1 gph, more water goes past the skimmer, than will go through it.

pods thrive in the DT, on a well running system--no need to turn your sump (an export facility) into a production facility. The pods in the DT are subjected to predation--and that is their purpose in life: food. When you produce in the sump, you add bio load to the system, which makes things harder for everything else. Algae grows well, regardless of flow rate......

RocketEngineer, gave just one example, of how "low flow" can affect a system. Algae--read excessive organics, being allowed to remain in the tank, being mixed back down into the tank, rather than being taken out faster, to the skimmer. (This is a rather complex topic to cover it well) As well as (not always) an undersized skimmer. By far one of the largest problems with marine systems is inadequate skimming, because there are no established standards on the sizing of skimmers. Again, this is a rather lengthy topic to cover well.

[Joe Blowfish]

Originally Posted by uncleof6

But your experimental data is incomplete. What is needed is the real world flow rate. It is nowhere near 600gph, let alone 700 gph, because, according to the advertising, the the ECO633 pump starts at 633 gph. By the time the plumbing is added to the static head (friction loss) you will be lucky to be above 200 gph. Nor have you stated that you are not running other equipment with the pump, which most do. The claim that it can flow 600 - 700 gph, is unfounded.

In my video I explain that I measured the actual return input into the display tank, after the head-loss my ECO633 puts 280gph into the tank. (I'm not running anything else off of this return pump). Based on my experiment, the 280 gph drains through 0.55 sq-in of slot in the skimmer bar.

The 600-700 gph estimate for 1.5" piping is an extrapolation based on the x-sec area increase from my 1" setup.

- youtube guy

[uncleof6]

Originally Posted by Joe Blowfish

In my video I explain that I measured the actual return input into the display tank, after the head-loss my ECO633 puts 280gph into the tank. (I'm not running anything else off of this return pump). Based on my experiment, the 280 gph drains through 0.55 sq-in of slot in the skimmer bar.

The 600-700 gph estimate for 1.5" piping is an extrapolation based on the x-sec area increase from my 1" setup.

- youtube guy

I rest my case. Suitable for a 28 gallon tank.

[Ted_C]

Well - I tried out the skimmer bar idea this evening with my first water test...

Good news is the stand held. Bad news is the skimmer bar needs re-worked.



Had two problems - one bulkhead has a minor leak and the skimmer bar didn't work.

As far as I can tell - two things happened - the slit was not wide enough (more to come on that later) and the 1" pipe running horizontal did fill up with water.

After the first test - a scary moment occurs as the water height in the DT goes well above the skimmer bar - sort of like what rocketengineer said. It drops almost immediately though and forms an equilibrium with the return pump as the drains equalize. It did not drop far enough to perform it's intended function though - surface skimming. The skimmer slit was about 1/8" underwater pulling a full siphon. I have no idea what my width of skimmer slit was - all I know is I cut it using a dremel and two thin-cut blades together.

So I took out the skimmer bars and cut the slit out to 1/8" thick with the dremel router bit and tried again. I had better results with this where it did do surface skimming - but only near the outlets. My best guess is the horizontal skimming pipes are filling up.

One more test - I took the skimmer bars out completely and let the three one inch drains (2 90's on each side and a t and a 90 in the middle). Surprisingly, the water fills the display tank to about 1/4" from the top of the 90's and T (meaning 3 drains are barely keeping up from the Eheim 1262 return).

I'm going to give the skimmer bar one more shot with 1 1/2 PVC skimmer bars, 1 1/2 fittings with 3 1.5" to 1" reducing 90's and a 1/4" skimmer bar slit.

[Ted_C]

ok - I give up... I can't get this to work. I couldn't use 1 1/2" pipe - it cant fit with the holes and the center beam. I tried a 1 1/4" pipe with a 1/8" slit (approx) - the water's still going over the skimmer slit instead of skimming the surface.

Here are some videos of the issue

Video
Video

I am going to order a black coast to coast today...

[Eurobeaner]

NoWaIgH. Et DeDnT wArK! pretty sure thats what everyone else said. here, i have a better designed "pipe" overflow. biggest mistake of my original build. my slit is much wider and drains on both ends.... still very very very low flow. i have a 700gph pump going through 9 90* bends and 3 foot elevation, AND SPLITTING BETWEEN 2 TANKS, and it STILL has to be throttled down to get this pos overflow design to work.






now, on my new tank, beananimal with 1.0" bulkheads going to 1.5" pipe, a mag 12 pushing 700gph with head losses to ONE tank has the siphon valve closed damn near fully. i could potentially flow 2000gph+ through this one tube and still have room for error.

(video::: dont mind the noise from the other tanks)

http://s1081.photobucket.com/albums/...t=29351df4.mp4

[uncleof6]

Originally Posted by Ted_C

ok - I give up... I can't get this to work. I couldn't use 1 1/2" pipe - it cant fit with the holes and the center beam. I tried a 1 1/4" pipe with a 1/8" slit (approx) - the water's still going over the skimmer slit instead of skimming the surface.

Here are some videos of the issue

Video
Video

I am going to order a black coast to coast today...

Like I think we tried to make clear, we are not trying to pick on people. Sometimes, ya just have to find out for yourself, certainly. However, how much time, and hassle it would save, if the voice of experience carried more weight than popular opinion. Even if the voice of experience does not carry the weight, the knowledge of physics should. Physics is not a bunch of theories, rather LAWS of Physics. You can't beat them, no matter how hard you try. I am sorry you had to find out the hard way. But your dedication is admirable.

Good luck with your C2C, and please use a siphon system in conjunction with it. BeanAnimal's design, is very very very hard to beat--at any flow rate.

[cheezischrist]

i forgot about this thread lol. i am no longer going with this idea, nor have the 75, i traded it for a 125. and i installed a 5" by 5" by 24" overflow box in it with 3 1" bulkheads and beananimals setup. getting glass 6' long was an issue, for me, and i have other plans for that area remaining,well science projects really. 1 aquaclear 500 refugium mod, to run during normal tank light hours, basically a pod factory, and another aquaclear 500 i plan on modding to be a LR rubble filter, but with a small drain line out of the bottom into a 5gallon tank behind the display, wich will be hosting a water wheel ATS design i dreampt up and then that will drain down to either the 30 long sump or be fed directly back to the display with a small pump. gonna be tinkering with it alot probably, but it keeps it interesting and i like trying to invent things lol. i decided against the skimmer bar after hours upon hours of reading, research, a few mock ups in old rubbermaid totes, and after all that i ended up being sold on the beananimal system. not going coast to coast, so i swayed from it a little, but if i decide to down the road i can always extend the box, or just add a second, and have my closed loop setup designed so i could if needed disconnect it change a few fittings and have my sump and fuge run through those lines temporarily till the overflow changes were complete and cured.

[picker]

> i forgot about this thread lol. i am no longer going with this idea,

Thanks for digging it back up, it was a fun read none the less. For completeness here is my failed version of a similar theory.

[new2dareef]

Hey Reefers, Im very new to this . Im setting up my first saltwater reef aquarium. Trying to read as much as possible and not make too many mistakes. Im going to try and set up a bean animal overflow on my 180 glass tank. I will have to use an internal overflow box and do some drilling. Im not afraid. Anyway my concern is light. I dont want the overflow box to block my lighting. Can I get some input on my possible solution. Im thinking of a 1" to 1 1/2" box inside the tank on the back wall and an external box with my drainage pipes outside. Im hoping three or four bulkheads connecting them will solve my issue. Any feedback?

[uncleof6]

Originally Posted by new2dareef

Hey Reefers, Im very new to this . Im setting up my first saltwater reef aquarium. Trying to read as much as possible and not make too many mistakes. Im going to try and set up a bean animal overflow on my 180 glass tank. I will have to use an internal overflow box and do some drilling. Im not afraid. Anyway my concern is light. I dont want the overflow box to block my lighting. Can I get some input on my possible solution. Im thinking of a 1" to 1 1/2" box inside the tank on the back wall and an external box with my drainage pipes outside. Im hoping three or four bulkheads connecting them will solve my issue. Any feedback?

Post this in the appropriate thread. Good luck getting your 50 posts.

http://reefcentral.com/forums/showthread.php?t=1541946

[Scubazaru]

I was looking at this overflow system on a few sites. Stumbled on this post doing research. People seem to have successfully have run the bar skim on 65's or less for quite a few years but nothing bigger than that that I have seen. When it comes to flow, I'm no expert but this guy is running 1.5" hole in the corner of his tank and that's it. Why is it he needs no surface skimming? http://www.youtube.com/watch?v=xifweoA0N4Q. I understand what its for but why are there some folks having success with no algae issues and some are having horrendous results? So my question is, even with the lower flow rates, if phosphates, nitrates, ect are mitigated in the sump, is algae still that huge of an issue? I understand what has been taught and it makes total sense, but how to explain the positive results some are getting with the skimmer bar while others are not ?