Beckett vs. Needlewheel skimmers

Roland is on point here. In a proper recirculating skimmer, bubbles arent making it down to the pump input, so nothing is being "broken off a bubble". What recirculatign skimmers do is 1) create a much stronger counter current in the skimmer, and 2) allow you to tune water input and air input independantly.

Point 2 is huge. I run about 200gph from my tank to sump. Running 700gph on my skimmer doesnt give me any advantage. It decreases contact time, without giving me access to any dirtier water.

With a general non recirculating skimmer, when you reduce air intake, you increase water throughput, which plays havok with the levels in the skimmer. Theyre much easier to tune, and much more consistent when you seperate the two.
 
Zephrant- I can see how tank volume might affect the performance of a skimmer, but I can't see how it would be a consideration in design. Is there something that I am missing?

I would think that recirc would work very well for tanks that are adequately skimmed. The increased contact time would remove molecules more resistant to exportation. But you trade that for volume flow through. This would not be a problem if the skimmer was adequate for the bioload of the tank.
 
So imagine now that we view the sump and the skimmer as a single system and we use the sump to hold the recirc water for the skimmer. Doesn't this mean that you are going to be less efficient when you start skimming the "already skimmed" water? Wouldn't you be better off just sending the skimmed water back to your tank and getting more "dirty water" (not yet skimmed) to process in your skimmer?
Click to expand...

Take that a step further, and think of the sump, skimmer, and tank as one system. See the point? Either way you're skimming diluted water.

I guess my thinking is this: the only place where I can really see an advantage to the "clean more water less well" over "clean less water more well" is in the situation where the skimmer is too small for the bioload.


In Escobol's papers, there much mention of certain things needing long contact times. High throughput skimmers dont have those contact times. A big, low throughput skimmer can pull out plenty of material, but also can pull out more of the "hard to get" stuff.

The point is, any decent skimmer is going to do a good job and pull out most of the waste, even with a low throughput. It just takes one with a really high contact time to pull out the tough to get last amount of waste, and I believe thats where recircs excel.


I think if you take a filthy tank, and put a beckett on it, it'll clean the tank up faster than the low throughput needlewheel will, but I dont ultimately believe that it will get it as clean in the end.
 
<a href=showthread.php?s=&postid=8276443#post8276443 target=_blank>Originally posted</a> by TurboSnail8898
But what if a Beckett has the same contact time as the recirc. skimmer?
Click to expand...
The only way to do that is with a recirc beckett skimmer , Now you need to add water to the skimmer .
I saw a MRC Recirc skimmer very large and bulky, they did not get to papular did they ?
 
recirc becketts are fine, but you have to rememeber that it really doesnt matter how the bubbles are made....

and you can make significantly more bubbles for less watts with a needlewheel.
 
Than its seems NW skimmers have the advantage. Becketts put a lot of water through them, but don't get the molecules that are hard to export. You can put just as much water through a NW by increasing the pump size.
 
<a href=showthread.php?s=&postid=8276561#post8276561 target=_blank>Originally posted</a> by hahnmeister
Ill throw this out there though... downdrafts and becketts are much better for raising ORP than NWs are.
Click to expand...
Not mine .
 
Alwest, et al,

I tested a OR 2700NW with adjustable air input to the intake side and it produced plenty of air, and I could tune the flow through rate with a valve before the intake, and adjust the amount of air with a speedfitting.

I thought the OR2700 was too noisy so I experimented with a Kent venturi before and after a Mag3 and Mag5. The foaming was very similar to the OR, but with less pump noise and I think less watts (as if I care about 20-40 watts in an entire house!). The air input (venturi) works great whether I adjust the flow rate from 100-150gph (Escobal suggests ~120gph for my tank).

I bored out the venturi slightly to optimize it for my flow rates.

I didn't like the noise of a Beckett.

Manufacturers pay a few dollars for a Beckett, and it's in vogue now. They pay $40 more for a Mazzei venturi and they're old news.

No need to re-circ if you get enough air into the water before it enters the reaction chamber the first time. Contact time is a function of how fast water goes from the entrance to the skimmer to its exit. Re-circ doesn't change that. Too much turbulence in the chamber is not all good. Not hard to make enough turbulence with a decent CC anyway.
 
kool thing with becketts you can push them a lot harder if you want to upgrade to a larger tank just add a bigger pump

I put a 1 1/2 hp, seahorse on my MRC-8448 to see what it could take it works good but the air intake sounds like a B-2 bommer taking off (what a suck zone)
 
One of the main things I have noticed about the beckett vs needlewheel debate is the pump size - in general needlewheel pumps are small and beckett pumps are hefty. Just wait until Reeflo releases their needlewheel impellers for their pumps. I think this will change many of the opinions of what a needlewheel skimmer can do.

Up to this point, there has been some sort of a line that NW units were good for (somewhere about 300 gallon system), after that it is generally considered that a beckett driven unit would be better suited to handle the system.

Another thing to think about, the Reeflo Dart is a flow rated pump, and it only draws 160 watts. This is a far cry from an Iwaki pressure rated pump.
 
Here is a chart I post every six months or so:
Beckett-2.jpg


That shows the water flow vs. air flow though a Beckett in to free air. For a Becket skimmer with the injectors mounted up above the water level, this can be used to approximate the water flow if you know the air flow, and vice versa. But you do need to match the test conditions- 3/8" tubing and valves or at least dual 1/4" inputs.

I don't have pump profiles though a skimmer available- I'd like to get watt, gph and scfh readings for various pumps some day.

Rich- Definitely room for debate. Is a 10x tank turn over though your skimmer per hour better than a 1x turn over? Answer: Depends on way to many other variables to have an single answer. ;)

As you know, Beckett skimmers are geared for high tank turn-overs, and shorter contact time. Most all aspirating skimmers are the opposite, which is part of the reason they perform differently. There is no doubt that both types work well, and both types have strong believers.

I believe your observations, but can't offer a theory without seeing the unit in action and pondering. I've not spent much time experimenting in what I consider "low flow" skimmer designs, as my personal preference is in high-flow skimming- Not for the skimming performance alone, but for the extra aeration and "safety margin" that it gives.

Let me expand on that a little- High air/water flow skimmers do have one clear trait- they can pull lots of "stuff" out very quickly. This is best observed by adding a foaming agent to your tank (Prime, or most antibiotic medications). The big skimmers will happily pull out gallons of water per hour- On the floor if you don't have an auto-shut off collection container. But this same feature is of tremendous benefit if something nasty happens in your tank- like a spawning event. IMHO, having a big monster skimmer sitting at the ready to pull out that kind of pollution quickly is very much worth the cost of power to keep it on "standby". It's the same reason I drive a V6 instead of a more standard 4 cyl in that car size- The power is there when I need it, even though it costs me more to run.

I run a skimmer that is more at home on a 500g tank, on my 200g system. so I'm also a believer of the "can't over skim" camp. :)


Doc- Water flow is just a way to get flow divided by volume, to give your contact time. Sometimes having the same data expressed in different ways can help with the analysis.

Al- I don't like to admit how low our power is up here- Too many people want us to pay more so they can pay less. :) I don't like to "waste" power at all, but the power draw of my skimmer is very low on my list of concerns about my tank. To post charts, you need to export to a JPG from Excel or something similar, then you can post it.

Turbo- The point I was stretching for was that perfectly optimizing a skimmer purchase decision by using one feature (air flow for example) can turn out to be insignificant when compared to other variables in an entire system. The "best" skimmer can't be determined without knowing all the above information.

Rich- The big oversight that Escobal makes is here: Page 84 ...experimental observation indicates that two turns a day will suffice to process the water." (Aquatic Systems Engineering, by P.R. Escobal, Second Edition)
He then goes on for 30 pages designing the perfect skimmer for that assumption. What are his qualifications to make that observation? Where is his PHD in Biology? How many years has he kept reef tanks, and how many different "turns" did he try on those tanks to come up with the magic number "2"?

Escobal's book is great on theory and numbers, but he looses all credibility when he fails to explain why 2 is the magic number of turns per day. That said, there is still lots of good information in there, and I recommend that everyone pick up a copy someplace. But look at it skeptically- Escobal is a great physicist, but I've never seen a shred of evidence that he ever kept a large reef tank, much less did the kind of testing necessary to come up with that kind of data.


Zeph
 
Zephrant
Good info, thanks for the chart, pressure would also be helpful in determining what pump can achieve what air/water flow.

I did want to vistit something you mentioned earlier.

“Dwell time- skimmer water volume, divided by input water in gallons per second gives the number of seconds that the average water particle will be "in play" in the skimmer. This is a very rough average, as it depends greatly on the skimmer design. Picture a long tall counter-current tube, vs. a short square box. Both could have the same dwell number, but very different performance. But for similar physical designs of skimmers, this is a good measurement.”

This is true, because the taller one will give more “hits”(air bubbles coming in contact with waste), but skimmer shape needs to be weight against the other factor that causes hits, that's air volume. Which one gives more hits, a tall skimmer or a short skimmer. If they both have the same volume with the same air Ratio. Like you say, everyone knows it is the tall one. If both skimmers have the same total volume and the tall one is receive 20 scfh of bubbles and the short one is receiving 30 scfh. Well it no longer as clear. As technology continues to improve (smaller, cheaper, pumps ability to provide more air per volume and watts) this will continue to have to be revisited when we choose a skimmer.

Its been clear with few exceptions that Becketts have had higher hit counts, and NW had higher dwell time. NW have been trying to increase thier Hit counts with more air, and Becketts are trying to increase their dwell time with bigger/add on body chambers. But the times their a changing, 60 watts 75-80 Scfh.

I think Doc g has it right, have one of each if possable. As rich pointed out, one for stubborn stuff, and one that processes more water faster. (forget about the ORP thing hahn, lol)

I agree with Doc G said if I would to choose one for a home aquarium I to would choice the one that scrubs better. If I had a store or big holding system with lots of rapidly changing bio-loads… then the high flow Beckett would be my choice. Ether way they both can be good skimmers.

And no one mentions Down Drafts skimmers anymore why is that? They seem to be even futher towards the faster prosesing of water than the becketts. If a little faster is good then is a lot faster better?

So is this it? On one side we have NW / airstone type skimmers long dwell time and on the other we have Down Draft type short dwell time skimmers. Then everything else falls inbetween.I wonder where Tunze Doc skimmers fall.
 
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Roland, or anybody else,

Can you guys elaborate on what different kinds of 'stuff' there is? I'm under the impression that any amphipathic molecule will interact with an air/water interface. It seems a little weird to say that one elaborate bubble making machine will pull different stuff than another.
 
JC VT the word i used was Stuburn. Not different.

I can find you a link on this later if you want. I think Randy has a actical that touchs on that.
 
<a href=showthread.php?s=&postid=8276561#post8276561 target=_blank>Originally posted</a> by hahnmeister
Ill throw this out there though... downdrafts and becketts are much better for raising ORP than NWs are.
Click to expand...

Hahn, I have heard this before about becketts being better for improving ORP but I'm not sure I understand it. Do you mean that if you have a low ORP a Beckett will raise it faster. I guess I can understand that in that the Beckett will process the water faster and therefore improve lower water quality faster? From this same perspective it would seem that if I am overfeeding my tank then a beckett would more quickly clean it up and get it back to the nutrient poor state I’m trying to achieve. Does this match with your understanding?

Roland, you are right. Recirc vs. circ should probably be a different thread. I was surprised there wasn't more excitement - probably means I didn't express myself well enough. If anyone thinks they really understand the science behind recirc (and I mean more than giving you better water flow control) feel free to pm me for a little offline discussion. I would also be interested in any articles on the more stubborn things that need longer contact time. Randy recently did a “What is Skimming?” article and I didn’t see any specifics on this. I’ve also looked through The Reef Aquarium volume 3 (a great book btw) and didn’t see much on that. I can intuitively understand why that might be the case but Zephrant’s point about Escobar’s assumption makes me wonder if anyone has really done the research to figure this out or are we all making assumptions. It’s also helpful to know how much longer it takes to get those stubborn molecules out of the water. For all skimmers, the window is pretty close. Is an extra 30 seconds good enough to get the stubborn ones? How about 3 minutes? What about 10 minutes? If it takes too long then no skimmer is going to get them. It would be great if someone had a chart that showed what percent you could get out by exposing a certain amount of water to a certain amount of bubbles by time, i.e. what percent you get out in 10 seconds, in 20 seconds, etc. up to 90+% removed. Has anyone every seen anything close to this?

WarrenG, I don't think the skimmer manufacturers decided to select Becketts just because they were in vogue. I tried to pick a list of the very best skimmers out there and I didn't see a pure venturi skimmer to add to my list. Do you know of a pure venturi skimmer product that can run with the very best of the needlewheel and beckett skimmers? For the same reason I didn't include any plain downdraft skimmers (shooting water against plastic media to make bubbles). It appears to me that they have been surpassed by the good beckett skimmers in terms of performance.

Zephrant, your last post was very helpful and has a wealth of new understanding (for me) in it. Thanks too for the tip on how to post charts. The thing about your chart that was confusing to me is that you used a Sequence 3600, which is essentially the Dart pump and maxes out at 12’ of head (just like the Dart). The Dart has a bad reputation for driving beckett skimmers (not enough head) but yet you show it doing almost 70 scfh. I believe your numbers but two questions arise. How can a 3600/Dart pump generate 68 scfh and why are the Austin Oceans guys (I think you’ve heard of these guys) quoting only 45 scfh for their single beckett skimmers on their website. Why don’t you tell them how to get 68 scfh with a Dart and maybe I’ll switch back from the ER RC500 to their beckett skimmer?

Let me try out some more analysis. If I try and compare a RC500 (with 2 new Gen-X 4100 pumps plus an Eheim 1250 to feed the skimmer (gravity feed for the skimmer doesn’t work in my setup) vs. the AO Foaminator MAX 5000 (Sequence/Reeflo Tarpon pump) and I want to understand the impact of skimming a 240 gallon tank and can compute a number of relationships. If I want to think about how long it will take them to skim the entire tank I first decide on my effective throughput:

Eheim 1250: 317gph*.8 (for head loss) = 253 gph (within the ER recommended 1-1.5x turnover)
Sequence/Reeflo Tarpon: 1440gph*.6 (more head loss) = 864 gph (within AO recommended minimum 800 gph per beckett numbers)

Does this look ok? I am estimating the head loss for feeder pump on the ER and estimating what the head loss is through the beckett? If anyone has better estimates please let me know.

Now, I can do some calculations on how long the skimmers will take to skim 240 gallons:


ER RC500
240/253 = .94 hours to skim one pass of the tank
24 hrs/.94 = 25.5 X turnover of the entire tank through the skimmer in a day
25.5 passes of the entire tank
25.5*240 = 6120 gallons skimmed (in a day)
(6120gpd*76scfh*24hrs)/1000=11,163 (airflow processed per day product?)

AO MAX 5000
240/864 = .28 hours to skim one pass of the tank
24/.28 = 85.7 X turnover of the entire tank through the skimmer in a day
85.7 * 240 = 20568 gallons skimmed (in a day)
(20568gpd*45scfh*24hrs)/1000=22,213 (airflow processed per day product?)

Now I’m not sure of this last “product”. More scfh applied to the entire tank seems like a good thing. It’s perhaps good now to consider the Deltec vs. the ER RC500 since they can both use the same Eheim 1250 skimmer feed pump and are similar designs of similar size. So the gallons skimmed per day will be the same. But I think the ER is probably doing a better skimming job because it processes more scfh for the same gallons per day.

If I do the same calculation on the Deltec AP902 I get:
240/253 = .94 hours to skim one pass of the tank
24 hrs/.94 = 25.5 X turnover of the entire tank through the skimmer in a day
25.5 passes of the entire tank
25.5*240 = 6120 gallons skimmed (in a day)
(6120gpd*56scfh*24hrs)/1000=8,225 (airflow processed per day product?)

This seems intuitively correct ratio wise when looking at just the Deltec and the ER. But I think I am missing something when comparing different style skimmers. I’m not sure how to use dwell time since a dual beckett has half the dwell time as a single beckett skimmer (same body size). Contact length seems like a good metric to include somehow but I’m not sure I understand how that would work for recirc skimmers. I’m reasonably comfortable with the pieces so far, gallons processed per day and scfh per day but the numbers seem to imply too great an advantage for the beckett skimmer. Any good ideas of other metrics and algorithms? Keep in mind that the obvious case of weighting how slow the water passes through the skimmer lets the needlewheel guys “beat” each other simply by specifying a slower feed pump so that doesn’t seem right. Maybe you have to look at scfh per water volume of the skimmer body to see how concentrated the airflow is with the water processed, perhaps including a component of contact length as a proxy for average bubble contact time (again not sure how this fits with recirc skimmers), i.e. how dense a concentration of bubbles you can achieve in a limited volume seems like an interesting metric and in that scenario longer contact paths should give better results.

ER recommends 1-1.5x turnover through their skimmers per hour. I wonder where they got that number? Is it just convenient or do they have some science behind it?

Some might say this is a hopeless quest and that this is too complex a subject to be reduced to a single number or two. However, there are some simplifying assumptions. First, I am certainly willing to limit this analysis to very good performing skimmers. So I can eliminate the pathological cases that might twist the results. Second, although some skimmers may perform better when slowing the water flow I don’t think I have too many qualms about letting skimmers that process water faster get higher scores. There are natural limits to how fast any skimmer can process water without failing (you have to get the bubbles into the water and then get them out of the water for return to the sump and this can only happen so fast) so even if you find you get better skimming by tuning the flow down slightly that still seems like a valid metric. Obviously a work in progress. Any advice or suggestions is welcome.

Al
 
Al, for what its worth, the ETSS 800 I had for a while was a much nicer skimmer than the dual beckett I played with.
 
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