Beckett vs. Needlewheel skimmers

[sherm71tank]

I have two shots. One is the Dwyer flowmeter showing almost 50scfh. The pump is 125 watts. Not bad?

The diffusor makes a big difference, at least on a beckett this size.

 

[alwest45]

<a href=showthread.php?s=&postid=8353552#post8353552 target=_blank>Originally posted</a> by sherm71tank
I have two shots. One is the Dwyer flowmeter showing almost 50scfh. The pump is 125 watts. Not bad?

What pump are you talking about that's 125 watts? Is the 125 watt pump driving 1 or 2 becketts and is that the pump that's producing the 50 scfh?

 

[sherm71tank]

It is driving one beckett in recirc. It is a Resun pump a little more than a Dolphin DP-1200 in flow rate. About 850 gph @ 12' head height. Yes it is the one producing 50 scfh. Using the maxi 1200 for feed pump.

 

[hahnmeister]

sherm71tank, 50scfh for 125watts is well...

Its all relative to the height of the skimmer too... A 6' tall skimmer may not get as much SCFH as a 3' skimmer, but it might pull out more due to contact time.

But just to give you an idea... the ATI bubblemasters do 80-90SCFH for a mere 60 watts. That might be an exteme enabled in part by how short the ATIs are, along with many BubbleKings, but thats still about 4x the SCFH/watt that you are getting. A Dart NW can do about 80-100scfh on its own on a 5' tall body, for what... 120watts about?

 

[sherm71tank]

Don't have any experience with the ATI's but they do look promising. I don't know where to get a Dart NW. The power curves I've seen on the Dart put it anywhere between 110 and 160 watts depending on feet of pressure.

 

[JC VT]

On the subject of darker skimmate and pulling more out of the water, does anyone have any reference on the actual science behind this.

Wet skimming, intuitively, pulls more out. The nasty stuff is locked up in a bacterium, food mass, detritus, etc.

Here's a quote by Randy Holmes Farley:

For this reason, I believe that the greatest skimming will come from removing a relatively wet foam, rather than waiting for this same wet foam to drain prior to removal. The only difference between a wet foam, and one that has drained more to form a dry foam, is that additional water, and some organics, have drained away. I believe that this important point is often neglected.

I understand the theory that if 10 seconds of dwell time get X amount of gunk out of your water and for 20 seconds you get X+Y out. For 100 seconds I suppose you get X+Y+Z and for 1000 seconds I suppose you could get even more (assuming even and adequate amounts of bubbles).

I think there is marginal utility in too much dwell (1000 seconds). A clean bubble will have more ability to take out 'stuff' than a dirty bubble. By extension, a clean bubble will be able to take out "stubborn" molecules better, also.

 

[alwest45]

<a href=showthread.php?s=&postid=8355446#post8355446 target=_blank>Originally posted</a> by JC VT
Wet skimming, intuitively, pulls more out. The nasty stuff is locked up in a bacterium, food mass, detritus, etc.

Here's a quote by Randy Holmes Farley:

For this reason, I believe that the greatest skimming will come from removing a relatively wet foam, rather than waiting for this same wet foam to drain prior to removal. The only difference between a wet foam, and one that has drained more to form a dry foam, is that additional water, and some organics, have drained away. I believe that this important point is often neglected.

I think there is marginal utility in too much dwell (1000 seconds). A clean bubble will have more ability to take out 'stuff' than a dirty bubble. By extension, a clean bubble will be able to take out "stubborn" molecules better, also.

Yes, I saw the article by Randy Holmes-Farley and I thought it was very useful. For those that haven't had a chance to read it (it's in the August 2006 issue of Reefkeeping) you should. Randy's opinion is an interesting datapoint and when you think through the physics involved it does make sense.

I didn't really mean we should shoot for 1000 seconds of dwell time. I'm just trying to understand if anyone really knows about getting these "stubborrn" molecules out of the water or not. I do keep hearing 90-120 seconds as a recommendation for dwell time but there does not seem to be any real evidence or research to back that up. And even if 2 minutes is the right number, does anyone understand what percentage you get out if your dwell time is less than 2 minutes?

When we say dwell time does everyone agree that it's bubble dwell time, not water dwell time? How do you calculate bubble dwell time? It's some function of bubble size, countercurrent flow, and turbulence I presume?

Al

 

[JC VT]

I didn't really mean we should shoot for 1000 seconds of dwell time. I'm just trying to understand if anyone really knows about getting these "stubborrn" molecules out of the water or not.

I didn't either. Theoretically a clean bubble with low turbulence would do the trick on a "stubborn" molecule.

On the other hand, no one in this thread has identified what a "stubborn" molecule is, if it exists, what it might be, why current skimmers would not take it out as well, why a needlewheel would get it out better than a beckett, and whether or not anything in your reef tank cares if its not skimmed out immediately.

 

[Roland Jacques]

<a href=showthread.php?s=&postid=8355810#post8355810 target=_blank>Originally posted</a> by alwest45

When we say dwell time does everyone agree that it's bubble dwell time, not water dwell time?
Al [/B]

Oh my goodness your right. I've been referring to as "dwell time" being water time only, I see where some may be using it as bubble time in some conversations. No wonder we have hard time communicating, that and my spelling. It seems that most people use it as water time.

I will in the future refer to them as "water dwell" and "air dwell" sorry about the confusion, good catch, thanks.

now that you point that out, I don't no enough words to describe the aspects of skimming. Anybody have a link to skimmers words & definition

 

[alwest45]

Roland, do you agree that water dwell time has nothing to do with removing organics? This assumes of course that it takes a bubble to remove organics. Is there any confusion on this point?

 

[sherm71tank]

Bubble contact time is what it's all about. But if you can make the same water make multple passes through a column of bubbles within the skimmer making the water cleaner with each pass then doesn't that make the harder to extract proteins more likely to be removed? If you take a skimmer can only be x% efficient then multple passes with the same water before being recontaminated seems like a good thing.

 

[alwest45]

<a href=showthread.php?s=&postid=8357646#post8357646 target=_blank>Originally posted</a> by sherm71tank
Bubble contact time is what it's all about. But if you can make the same water make multple passes through a column of bubbles within the skimmer making the water cleaner with each pass then doesn't that make the harder to extract proteins more likely to be removed? If you take a skimmer can only be x% efficient then multple passes with the same water before being recontaminated seems like a good thing.

I'm not sure this is correct. Rather than concentrate on trying to scrub the last bad stuff from your water in the skimmer and letting the easy to clean organics stay in your tank, it seems like you should get all the low hanging fruit first since it is quicker and easier. When you've gotten all the easy to clean molecules out (which I'm assuming is the majority of the organics that a skimmer can remove) then you can try to get more stubborn molecules (whatever they are) out. This is a little like cleaning the glass (acrylic) on the front of my tank. I don't want to focus just on cleaning one small spot to perfection - I want to clean the entire front glass first. Then when that's done, I can focus my attention on cleaning those spots of stubborn coralline algae that didn't come off in the first few passes.

Again, can anyone point to some data on what these "stubborn" molecules are?

 

[Roland Jacques]

<a href=showthread.php?s=&postid=8357501#post8357501 target=_blank>Originally posted</a> by alwest45
Roland, do you agree that water dwell time has nothing to do with removing organics? This assumes of course that it takes a bubble to remove organics. Is there any confusion on this point?

No I don't agree,

When most people talk about dwell time I they are talking about water. I think we assume that air bubbles are a given. So with that assumption water dwell does have a lot to do with removing organic. You question as to how much of a factor is it is a valid one. it can be tested easaly

Typically we cant control bubble dwell. This is a given, for a particular skimmer design. For the most part, we cant make a bubble speed up or slow down it's time in a skimmer. We just want the maximum air dwell and air volume while maintaining the smallest possible bubble as possible( with the bubbles still being able to rise to the foam). so i believe most conversations about dwell is talking about water time interacting with bubbles IMO. "Contact time" may be a better name but even that is a little bit misleading and not 100% accurate. Water dwell is what most of this conversation has been about. Hits or bombardments may be better words I need to look them up but most of my book are in storage.

<a href=showthread.php?s=&postid=8352935#post8352935 target=_blank>Originally posted</a> by alwest45
Roland, I hear you. But in a typical? sump & needlewheel skimmer setup the skimmer is fed by a feed pump. Those Sedras won't suck enough water from the sump to get the 1-1.5X turnover that Euroreef recommends (as 1 example). If you are feeding your needlewheel skimmer with a feed pump is there any difference in head between the circ and recirc versions? If there is, it seems like it would be a lot less than 25%?

Al

Al,
I missed this one
The answer to this is yes. The NW200 in sump skimmer (no feed pump) i tested in 4" of water it pulled 8 Scfh of air when i raised the water level in the sump up to 10" it pulled 11 scfh so head pressure does reduce the amount of air recirc Vs non recirc. In this real example test the results were 35% incease in air.

And the other point here is those sedra well suck to much water. The in sump skimmer pulls to much new water in it. The insump skimmer pump move 300-600 gph on a skimmer rated at 100 gallons. The recirc allows you to slow that down to 150-200 for you 1.5 - 2 Xs this is the main reason people want recircs, to slow down the flow.

This leads to a simple test about stubborn proteins question. you can simply compare identical nw recirc skimmers with different flow rates. See which pulls more and or stankier poop. I would imagine this test has been done many times. But ive never tested that.

 

[Fudge]

Hello all,

My eyes are buggin from this, very informative thread...unfortunatly im still a bit lost when it comes to the numbers involved.

Maybe someone could help me with the math here ..

I am Currently running a Quad-beckett, a 5800-1100 series sequence for recirc, an 8" body 40" tall with a diffuser plate for a little less turbulence.
It is fed with about 600 gph tank water.

I am interested always in ways to make this power hungry tank a little more economical...but dont want to downgrade at all.

I would like to build a 20" diam 36" tall NW dart...or dual dart ?
This is where im getting lost.

Does that mean i could estimate i see about an average of 180 total scfh now... so 2 darts is the only way to get those numbers? Even then, the only improvment would be the 20 scfh difference the 2 darts are, at an average of approximatly 200 scfh ?
It would seem ive just lost the power consumption improvement.
So im left with the differences in the tube diam to increase contact time,or to change water dwell times to make it a worthwhile project ?

Im just baffled trying to figure out water and air dwell time from one to the other.

So given the chamber sizes above, how would that skimmer be an improvement over my existing one....or would that even be one at all ?
What would be your guess as to the way to make a better improvement ?

Thank you for any help anyone who want to take a stab at an answer.
i apologize if this derails the thread in any way.
Marc.

 

[sherm71tank]

If you are going to use a large air pump like an Alita then why not just make a large cc skimmer? I've seen some really nice ones around here and they work great if you have room for one.

 

[Roland Jacques]

here is a link to a skimmer build using a dart pump. A dart NW can get about 170 scfh with a air pump.
hes built a nice tinymight skimmer
He trying a new wheel this time but i dont no if we understand the mesh wheel good enough yet to take full advantage of its ability to produse bubbles. i think the tiny might may be a better choise than a dart for the lowest watts mesh wheel bubble pump, just a hunch.

http://reefcentral.com/forums/showthread.php?s=&threadid=950690&perpage=25&pagenumber=2

 

[hahnmeister]

Ahhh, the old argument of dwell time vs. contact time. You know, of all the arguments and discussions I have had here over the years, I have never had a scientific or informed response to the question of 'can contact time mean dwell time?', as in, does the ideal of a 120second dwell time mean the time it takes one bubble to make it to the top, or the time the water spends in the skimmer. I would love it if someone would finally respond to this.

From all of the research I have done, I have gotten this. They are not the same, but, with enough exposure/contact time, the dwell time can be made up for. So there are some of these harder to attract proteins that need a longer dwell time to get taken out. Ok. I get it. And if the turbulence is too high, or the bubble gets to the top and the protein isnt exactly ready... well, what does happen to it?

A 120minute dwell time suggests that the bubble and protein have been together for some time... and since the bubble doesnt stay still, the protein must travel with it. I cant find any other way to explain it, or other way that these proteins would arrive there. Well, on a larger skimmer, or at least one with a decent foam head... what happens to these proteins if they reach the top of the skimmer and the end of the bubble's path? Well... unless they shake off before they reach the foam head for some reason, they would in effect stay in the foam head, right?

I mean, sooner or later, the multiple passes of a recirculating skimmer would mean that the harder to skim proteins will make it to the top portions of the skimmer. This explains the performance advantage of recirculating skimmers, even if you compare one with the same size pump/air throughput and skimmer body. This also explains why a beckett tower can churn out such vile filth. Becketts are the antithesis of a recirculating needlewheel or countercurrent skimmer. They blow tons of air bubbles down downdraft looking turbulent towers where the violence would suggest that there is little to no dwell time going on. Its the exact opposite of a Bubble King... yet it still performs very well. The bubbles then get deflected from their downward path in the 'black box' at the bottom, and the bubbles shoot up into the riser area where the foam path is pretty short. The water makes a quick pass in the black box and is out of the skimmer. The foam head starts pretty low in these guys, and it very tall. The contact time and dwell time are little to none... but they have tons of foam head where proteins can get trapped and get the rest of that 120second exposure in dwell time. Not in the water, but in the head. In this respect, the BK and the Barr Beckett are very much alike. BKs arent very tall skimmers mind you, and that bubble plate doesnt exactly make for a longer bubble path than a mixing pump with a downward facing output... but it does make for a stable foam head... a thick foam head.

I think that with enough passes and a nice foam head, a recirculating skimmer that is only 24" tall can extract those 120second proteins. Dwell time is a great goal, but if you dont have a 6' skimmer, then a muti-pass (recirculating downdraft) and a thick foam head can make up for it.

 

[alwest45]

<a href=showthread.php?s=&postid=8358741#post8358741 target=_blank>Originally posted</a> by Roland Jacques
No I don't agree,

When most people talk about dwell time I they are talking about water. I think we assume that air bubbles are a given. So with that assumption water dwell does have a lot to do with removing organic. You question as to how much of a factor is it is a valid one. it can be tested easaly

Typically we cant control bubble dwell. This is a given, for a particular skimmer design. For the most part, we cant make a bubble speed up or slow down it's time in a skimmer. We just want the maximum air dwell and air volume while maintaining the smallest possible bubble as possible( with the bubbles still being able to rise to the foam). so i believe most conversations about dwell is talking about water time interacting with bubbles IMO. "Contact time" may be a better name but even that is a little bit misleading and not 100% accurate. Water dwell is what most of this conversation has been about. Hits or bombardments may be better words I need to look them up but most of my book are in storage.

....

I do think we have a difference of opinion here. I understand the difference between bubble dwell time and water dwell time but it seems to me that the one that really counts is the bubble dwell time. How does it matter if the water in the skimmer is being recirculated back through the skimmer body or recirculated back through the sump and then back through the skimmer body (or even back through the tank, then the sump, and then the skimmer body)? It's just water being pumped to some other location before it gets a chance to be exposed to bubbles again and maybe give up some of the organic molecules it is carrying to the air/water interface. Why does the amount of time that water spends in a skimmer body matter? Why can't you get different water directly from the tank (it's probably dirtier water so it will likely give up it's organic molecules easier) and use that instead of recirculating the same water over and over inside the skimmer body?

Roland, I totally get the flow control issue with recirc skimmers. But it seems that many other people believe that recirculating water inside the skimmer body will make for a better reef tank and that their water will somehow be "cleaner". I don't see how the overall reef tank water quality improves by recirculating the skimmer body water.

Isn't the real key here how much bubble dwell time you can get? Because it's the bubble that will do the work. This is leading me to think of a point Zephrant mentioned some number of posts back in this thread about contact distance. Isn't that going to be a very important factor, i.e. how many inches the bubble has to travel from when it is generated until it escapes out the neck of the skimmer? Of course you have to look at other factors like how fast the bubbles travel over this distance and whether turbulence causes bubbles to be destroyed before they can reach the neck but I am thinking that the bubble contact distance and bubble dwell time are much more important that water dwell time inside the skimmer body.

(Please pardon the poor artwork skills)

Why is the first picture any different from the second?

(pictures fixed)

 

[alwest45]

<a href=showthread.php?s=&postid=8362458#post8362458 target=_blank>Originally posted</a> by hahnmeister
Ahhh, the old argument of dwell time vs. contact time. You know, of all the arguments and discussions I have had here over the years, I have never had a scientific or informed response to the question of 'can contact time mean dwell time?', as in, does the ideal of a 120second dwell time mean the time it takes one bubble to make it to the top, or the time the water spends in the skimmer. I would love it if someone would finally respond to this.

.....

Hahn, I think I get everything you said except I still don't understand why water circulating inside the skimmer body is somehow better than new water from the tank. Unless of course you need to first strip out the "easy" molecules so they don't crowd out the "stubborn" molecules and thereby give them a better chance to connect to the bubble? I agree that I don't see how the bubble can attract those stubborn molecules unless it can weakly attract them much earlier and then use the rest of the 90-120 seconds (or whatever it takes) to build a stronger bond that will allow it to keep the "stubborn" molecule all the way up the neck. But rather than give all the extra "capacity" away trying to get the "stubborn" molecules, wouldn't it be better to first go for the easy to attract molecules? That way you are removing the largest amount of gunk first and when you get the easy to clean molecules out of the way then your bubbles can work on sttracting the stubborn molecules.

Also, do you think that a well engineered, tall recirculating Beckett skimmer would perhaps be the best solution? Any idea why the Beckett skimmer guys don't seem to be jumping on the recirc bandwagon, at least not to the extent that the NW guys are?

 

[hahnmeister]

I would say that the proof is in the puddin... recircs, even those that use the same size pump and body as a single-pass, get more out.

As for the contact time making up for dwell time, I covered it in my last post pretty well... The proteins, even if they are more stubborn, are going to get taken upwards inside the skimmer anyways due to the updraft. I agree that a bubble dwell time is the ideal, but it can be made up for with good head and recirculating... at least thats what Im suggesting.

Or, perhaps its not even the dwell time, but other chemistry at work. Its no secret that higher ORP results in better skimming and waste handling. And even without an ozone generator, a skimmer does buffer the ORP. Perhaps the lower throughput of the recirculating skimmer allows it to reach a higher internal ORP, therefore allowing it to achieve a much higher skimming.

I have heard reports from people that the super saturation that ETSS and other downdraft skimmers provide gave their tanks a much higher ORP than running a needlewheel. It was unexpected when someone told me that, but it does make sense.

Perhaps its the ORP...

And yes, watt for watt, Becketts start to make more sense when you get into systems that are over 300g. Needlewheels have the advantage of lower watts in smaller sizes, but as you get taller, needlewheels tend to choke out on the head-pressure, and you start to see more pumps... so that single 50-60 watt mixing pump just got multiplied by 4 or 5... thats 400+ watts! now Becketts dont look so bad.

But there are the exceptions. ATI has been able to pull 100scfh with an eheim 1262 NW, and Bubblekings do even more with less wattage. I would say that a large Dart Needlewheel would also be a contender... able to work on 5' tall skimmers with ease and generate scfh numbers that would make a beckett skimmer cry.