Comparison of Recirc vs. Needlewheel skimmers.

S

scubaduderon

Member
I am in a bit of confusion on skimmer theory.

I see needlewheel skimmers with much large capacity numbers (size of tank served) as compared to recirc needlewheels of the same physical size.

When skimmers of the same size are compared with these technologies it seems the straight needlewheels win out. Why is this? It would seem to me that a recirculating model would be able to skim to a lower protien content than a straight needlewheel. Is this correct? Am I missing something?

Thanks,

Scubaduderon
 
I'm confused on what you are refering to. Most recirc skimmers use needle wheel/ venturi pumps for the recirculation. I'm guessing you are talking about the difference between needle wheel recirc and non-recirculating. Correct?

If so where are you reading this? Take a look at a Deltec skimmer which is a needle wheel recirc skimmer and then compare it to a ER or ASM that is a similar size. The recirc can handle a LOT more volume...

Rich
 
you really can't compare based on manufacturer's numbers. they put whatever number on the box that they think will sell the most skimmers.
 
A single pass skimmer (ER's CS & RS lines, stock ASM, etc.) involve using the mixing pump as the feed for the skimmer as well. If the skimmer is in shallow water, or water lower than the skimmer's water level, this cuts down the pump's capacity pretty fast (NWs are bad w/ back pressure). The water that enters the skimmer then only gets one pass with bubbles before it has to exit the skimmer...often the outlet is only inches below the pump's discharge, so alot of the water simply passes through...and rather fast. Even though those needlewheels arent as fast as a regular pump, they still often pump many hundred gph...that means a shorter exposure time, and this also means microbubbles have an easier time getting out into the system.

Now, for recirculating skimmers like modded ASM, ER's RC series, H&S, deltec, etc...
The water is fed in at the top usually, at a rate that is often a fraction of a single-pass skimmer's rate. That means that the water must pass from the top to the bottom, through a storm of bubbles on the way (no easy ways out the drain), and at a rather slow rate (usually recirc skimmers are fed at 1.5-2x the tank volume per hour). This downdraft path for incoming water greatly increases the exposure of the water to bubbles. This lower rate also means that microbubbles cant escape as easy...the output is just too slow. So then the pump can be made even larger for more bubbles, more capacity, etc. The pump is also drawing water from the same height it is drawing from, and so head-pressure doesnt factor in to the pump's back-pressure. The skimmer is fed with a seperate pump and doesnt make a difference if the water level around the skimmer is 1" or 20"...the pump's throughput no longer is effected...it can always operate at maxmum capacity and minimum back-pressure.

For these reasons, the recirculating skimmers are better performers than single-pass skimmers.
 
Still confused

Still confused

<a href=showthread.php?s=&postid=7020846#post7020846 target=_blank>Originally posted</a> by hahnmeister
A single pass skimmer (ER's CS & RS lines, stock ASM, etc.) involve using the mixing pump as the feed for the skimmer as well. If the skimmer is in shallow water, or water lower than the skimmer's water level, this cuts down the pump's capacity pretty fast (NWs are bad w/ back pressure). The water that enters the skimmer then only gets one pass with bubbles before it has to exit the skimmer...often the outlet is only inches below the pump's discharge, so alot of the water simply passes through...and rather fast. Even though those needlewheels arent as fast as a regular pump, they still often pump many hundred gph...that means a shorter exposure time, and this also means microbubbles have an easier time getting out into the system.

Now, for recirculating skimmers like modded ASM, ER's RC series, H&S, deltec, etc...
The water is fed in at the top usually, at a rate that is often a fraction of a single-pass skimmer's rate. That means that the water must pass from the top to the bottom, through a storm of bubbles on the way (no easy ways out the drain), and at a rather slow rate (usually recirc skimmers are fed at 1.5-2x the tank volume per hour). This downdraft path for incoming water greatly increases the exposure of the water to bubbles. This lower rate also means that microbubbles cant escape as easy...the output is just too slow. So then the pump can be made even larger for more bubbles, more capacity, etc. The pump is also drawing water from the same height it is drawing from, and so head-pressure doesnt factor in to the pump's back-pressure. The skimmer is fed with a seperate pump and doesnt make a difference if the water level around the skimmer is 1" or 20"...the pump's throughput no longer is effected...it can always operate at maxmum capacity and minimum back-pressure.

For these reasons, the recirculating skimmers are better performers than single-pass skimmers.
Click to expand...



Better performers, yes, but I often see skimmers with similar internal volumes where the straight needlewheel has a larger rating than the recirc type.

I was theorizing that because the recircs are more thourough they were rated lower due to the fact that they would overflow or pull too much wet skimmate. Being less thorough, a straight needlewheel type would not have this problem and even though it didn't pull as much skimmate it passes so much more water that it gets a higher rating.

Example: if the straight needlewheel was 1/5 as efficient as a recirc but passed 7 times as much water it would pull out more goo and get the higher rating.

I just ordered a recirc and these competing thoughts are running through my mind.

Thank you for your help so far folks but I'm still confused...

Ron
 
Hahnmeister puts it very well. The output of my non-modded ASM G-3 is very dependent upon sump water level. This would not be the case if I got the recirc mod on the unit. I still get excellent skimming, but have seen recirc units pull out even more.
 
So then....

So then....

the recirc skimmer pulls out skimmate even when protien levels are very low in the water. That is what I aml after, the lowest level of contaminants possible.

Dwell time should be maximised and the interface between the bubbles and water should be as calm as possible, so as not to disturb the developing high protien area rising in the skimmer.

Ron
 
You got it right Ron. I like recircs because you can control the water height independant of the air intake and vice versa. Its much easier to adjust for wet vs dry skimmate. Since the same tank can go from high to low protein/nutrient levels quickly, its nice to be able to adjust for it. The last several skimmers I've run were all recirc (ER, H&S, BK, Deltec) and now I'm using a non-recirc on a holding tank and I hate it. Maybe if I wasn't so used to externals, I'd like it more. Another benefit is that the pump is not submerged so it adds less heat to the tank. Mostly though - I love gravity feedind externals RC from the the overflow. The overflow water will always be the dirtiest, and you are certain that the skimmer body is filled with 100% surface water - not just recirculating the same sump water.
 
I'm planning my skimmer in sump.

I'm planning my skimmer in sump.

Does the water level in the sump affect the performance of a recirc skimmer as much as a straight needlewheel? In order for me to fit the skimmer I wanted into the sump I had to change it to a rubbermaid 15 gallon tub. The water level is about 4 inches deep. I realise I could put another higher container inside the tub but I would like to avoid that if possible.

Also how do I plumb the overflow to the skimmer? Currently I have a 1.25 inch inside diameter hose running from an overflow to the sump. I run about 400 to 500 gallons an hour through the sump.

Thank you,

Ron
 
Well there is another reason why a recirculating would be better for you. ;-) If you run a recirculating skimmer in-sump, the water level will not affect your skimming - so long as you feed it with your overflow (which is always preferred). If you fed it with a powerhead, it would - if your water level fluctuated in the sump.

You do not have to run all 400-500 thru the skimmer though - a simple ball valve and a "T" should do the trick.
 
I am getting a new asm g-3 for 219.99+tax wich is a great deal, there is a lfs that quoted me that about 6 months ago and is willing to honor it!!! however I am wondering if it is really dificult to make into a recirc model, Im not the best DIY'er and would hate to damage my investment....anyone here know what exactly Ill need? sorry for the hijack but it kinda falls under this topic. I have a 150g 60x24x24 and Im planning on doing a sps tank but dont know if this will be enough skimmer for what I want to run...modded or not?
 
I would check that monstrous ASM Club thread. There are lots of mods in there for you. I love your avatar. SHO NUFF. My favorite terrible movie, I think I know every line. ;-)
 
I'll give it a try, but...

I'll give it a try, but...

I'm a little curious how it will work though.

Currently the overflow has no restriction on it therefore no back pressure. If I put a restriction on it to feed the skimmer won't this affect the rate at which the sump fills? I can picture the water rising up through the tube running to the tee. It will reach a height at which forces are equal. I don't know what this will do to the overflow. There may be a tricky interplay between everything. If I restrict the flow out of the overflow too much it could potentially flood my room.....

How have you handled this? Am I thinking too hard here?

Ron
 
I will be dealing with this soon and I have always thought that one should have the water coming from the overflow run through a sponge or filter sock before the skimmer....wouldnt that make more sense? I would think that skimmer cleaning might be neede more often if not!?!? I guess the skimmer can remove particulate matter but for the heavier stuff I could see it laying on the bottom of the skimmer....
 
Take a look at asmskimmer.com for info on mods. It is relatively straight forward but does require drilling into your new G3. Good Luck.
 
scubaduderon, you said,
"Better performers, yes, but I often see skimmers with similar internal volumes where the straight needlewheel has a larger rating than the recirc type."

Show me. I have never seen this myself, as usually with the two skimmers with the same capacity, one recirc, one single-pass, the recirc has a much smaller body with the same size pump (or larger).
 
Here's an example

Here's an example

<a href=showthread.php?s=&postid=7024055#post7024055 target=_blank>Originally posted</a> by hahnmeister
scubaduderon, you said,
"Better performers, yes, but I often see skimmers with similar internal volumes where the straight needlewheel has a larger rating than the recirc type."

Show me. I have never seen this myself, as usually with the two skimmers with the same capacity, one recirc, one single-pass, the recirc has a much smaller body with the same size pump (or larger).
Click to expand...

Try these 2:

Pacific coast Imports PS-2000 Protein Skimmer with needle wheel impeller 5.85" Diameter 21.45" High up to 300 gallon aquariums.

RPS-2000 Recirculating Protein Skimmer 5.85" Diameter 26.52" Tall with needle wheel impeller for aquariums up to 185 gallons
Footprint 7" x 15"

Similar internal volumes but the recirc has a much smaller stated capacity. Why?

Ron
 
Also check H&S they rate in and out exactly the same:

In sump 150-F2001 Rated for 225 gallons
Pump: AquaBee 2001/38w
Diameter: 6"
Height: 20"
Footprint: 7"x14"

External A150-F2001 rated for 225 gallons
Pump: AquaBee 2001/38w
Diameter: 6"
Height: 26"
Footprint: 7"x16"
Actually 6" taller but I believe this is done becasue the pump inlet is now higher on the body
 
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