Reefkeeping article

[CAPT PETE]

Frank,

Very interesting article in the new reefkeeping issue. I have a Bullet2 and it was interesting to find out how it originated. I was wondering why you have the beckett assembly raised several inches rather then directly screwed into the base like I see everyone elses. Does this have something to do with contact time of the bubbles? Also, would you recommend a more powerful pump then the Mak-4. Can't wait until the next article.

Thanks,

Pete

 

[FMarini]

Capt Pete:
My very first Q?. Many thanks.

Actually the reasoning behind posting this article was to show what it actually take to come up w/ a skimmer which you and i have in our sumps. We really take all of this for granted, and its actually a lot of work.

So to answer your question.....
the more pump you put behind any beckettheaded skimmer the more water you'll process, th emore air you'll mix in and the more skimming you'll get.

The long extension pipe is exactly what you describe, it gives longer contact time, but it also elevates the beckett head above the water line in the skimmer (I mention the end terminal applications of a becketthead in the "How does it work" section of the article)

A Mak4 pump is more than sufficent for a small to med sized tank, if you have a tank bigger than 200gals consider a bigger pump. I find that the shorter the tubing between the pump and the becketthead the better. One method i find works well is to add a ball valve to the outlet of the pump, this way you can dial back the amount of water leaving the pump. Should you purchase a larger pump, you can alway run it on different sized tanks.
One easy and quick fiz to get more skimming power is to call Mike and request (read order/buy) a custom sized neck/collection cup. A slightly taller/ longer one will allow more air processing and more foam handling. This way you can elevate the water level in the skimmer and still get efficient skimming.
I hope this answers your Q.

Good luck w/ your tank
frank

 

[CAPT PETE]

Frank,

Do you find that adding the extension to the beckett assembly makes the skimmer perform better? Is it noticable and is it worth adding the modification? Also, if it makes the skimmer perform better why is this a modification rather than a standard feature from the manufacturer? Just curious.

Pete

 

[FMarini]

Pete:
Great q?
The extension pipe is a tricky situation. According to Chris Paris, the pipe should increase the intake of air, it should also increases the reaction time between organic laden water and air.

Do i think adding the extension pipe makes a big difference? not really/maybe, I do notice more foaming using the pipe, but my removed waste amount seems to be the same.

We intially had the pipe attached because we wanted to ensure the beckett was over the water level in the skimmer body.
Why is it not included as a standard feature? The skimmer seems to work fine w/o it. It just might work marginally better w/ it. So this might be useful if your trying to extract every last bit of skimming power out of your skimmer.
HTH
frank

 

[cwa46]

I have been planning the construction of a 6" DIY counter current skimmer with airstones. The one drawback that I see is the maintenance of the airstones and was looking at aspirated skimmers for a way around the problem.
My understanding was that "contact time" was the primary issue with skimming. My CC is designed at 150 gph to maximize contact time. If I change to an aspirated skimmer like the bullet, the flowrate has to be in the 850 gph range to deliver enough air. That turnover rate reduces contact time and skimmer efficiency. Please explain how I am view this incorrectly, or is an aspirated skimmer inherently less efficient than a airstone/CC skimmer? IF so how much do we give up to get a "set and run" device.
Another question I have is why aren't skimmers square? The flat material is easily worked, less expensive and a square shape provides a larger sq. area for contact.
Any enlightenment would be appreciated.

 

[FMarini]

Hi
Thanks for the question.
"Why aren't skimmers square"?
Great question, they certainly can be. I have seen a number of DIY skimmers including a square HSA1000, and they seem to work fine. My guess its that circular designs faciliate better water dynamics (total guess), but for the DIY'er square can work.

As i see it, the dilemma we're faced when processing organic laden water in a skimmer is contact time. So you really have two choices (again, as I see it) you can a) either build a tall skimmer which will have long contact times via slow flow or b) have a short skimmer (w/ reduced contact times) but processes 4-5X more water, so any inefficiency in removing waste the first time could be removed during the second or third pass.
{I'm not sure this came out right}
I guess what I'm trying to say is that the shorter skimmer (like this bullet) make up for their shortness by being able to process alot more water. So the bullets efficiency maybe reduced in comparison to a tall skimmer, but it makes up for its shortness by being to process the same water multiple times.

The reason the bullet is short is so it can fit underneath a cabinent, this was a design tradeoff, I suspect your skimmer and even the DIY skimmers i have seen are 4, 5, 6ft tall and use airstones. These skimmer work great, but now you have a new piece of furntiture.

So to answer your question directly if you are comparing a single pass of water, on face value I would guess that the shorter skimmer could possibly beless efficient. However, we never really measured this.

One point about contact time, or should i say contact distance. In the article by Chris Paris, he cites an article in which someone calculated the distance needed for an airbubble to become maximally saturated w/ organics. That distance was 13inches (if i recall correctly). So after 13inches, its unclear whether any more distance is useful or required.

Another thing to consider for determining efficency is the amount of air you can mix in w/ the water (number of bubbles and their sizes). IME the beckettheads makes far more bubbles (which appear finer in size) than a brand new airstone. This might also increase the amount of organics removed as well (since there is more surface area w/ more bubbles). So I'm not totally sold on the idea that these shorter skimmer are less efficient.

For your information a beckett head is not considered an "aspirating" valve, its a venturi. The aspriating skimmers are the euroreefs, DAS, turbofloaters. These skimmer utilize a unique impellor which "aspirates" (drawns in the air) and chops it into microfine bubbles.

I'm not sure if i answered your question, as I think i just rambled about a few ideas and hopefully they are coherent. Maybe what i can do in upcoming articles is actually compare a tall skimmer w/ low flow and one of these superduper skort skimmer which processes alot of water.
Please feel free to email if i don't make sense.
frank

 

[cwa46]

Thanks for the info on "square" skimmers.
As far as skimmer efficiency, I am more confused. Let me say that I am no expert, but I have been reading "Aquatic Systems Engineering" by P.R. Escobal. In chapter nine he discusses protein skimmer design. On page 93 and in italics to indicate importance he states; "This proves that it is better to have a higher bombardment rate per pass than to have more passes of water through the skimmer at a lower bombardment rate." The bombardment rate is the ratio of the turnover time in hours and the dwell time of the air bubbles in the skimmer.

TOTAL HITS = T/Ta

If his equation is valid and I understand it correctly, then using a Venturi method of introducing air into a skimmer reduces the total skimmer efficiency. The more water needed to draw the required air, the smaller the dwell time for air becomes reducing efficiency. Also, decreasing the time for one turn or T by increasing GPH also reduces efficiency.

Now having said that, I still don't like the maintenance and costs of airstones and hope there is another efficient way to introduce air into a skimmer. If the Venturi method is as much as 30% less efficient as Escobal suggests, do we just build them bigger to make up for it.

Based on Escobal's sizing I need a 6" dia. unit now. If I use a Venturi, I will need an 8" or 9" dia unit 5-6' tall. To drive something that large with a Venturi, I will be in the 1500 gph range.

Unless you see it differently, I think I will stick with air stones.

 

[CAPT PETE]

Frank,

What do you think of this?

http://members.cox.net/smokie/

Thanks,

Pete

 

[FMarini]

CWA:
I am familar w/ Ecobal's text, and I am familar w/ the concept you cited. He is suggesting a slower flow w/ maximal dwell time. Agreed.
If i recall correctly, airstone driven counter current skimmer like the kind you describe are considered the most efficient, no dispute. However hobbists have sought alternatives to cleaning/changing airstone, frequent air pump diaphram replacements, and having a 4, 5, or 6ft skimmer sitting next to their tank. These alternatives has created the shorter skimmers which skim exceptionally, becuz the produce tons of micro bubbles and skim very efficenctly. However in tradeoff they are energy hogs (as they require serious horse power to work efficently;yes pumps up to 1200-1500gph).

So I will leave you w/ this statement, there are theoretical concerns on maximal skimming and then there's reality.
The reality is w/ an appropiate pump, a beckettheaded skimmer will skim efficently, more than likely, more efficently than you will ever need, and should require less adjusting than an air powered CC skimmer. It really wasn't until the MTC HSA1000 came out did people start talking about the concept of overskimming.

Will the skimmer your making work well...you bet.

If you would like we can discuss the pumps sizes required to efficently run the MTC HSA250, or bullet1. These skimmer are of very short stature(under 24" 6" wide reaction tubes), use mag18 pumps, and also skim exceptionally well.
If you have had a chance to see a beckettheaded skimmer in action, I think you would be equally convinced.



Pete:
Thanks for the info. I have not seen this before and its is exactly what I was talking about in the other thread (in this forum). I've been buggin Mike for a easily cleanable screw-together bullet. As you know the beckewtt company has chenged the shpae of the outside of the beckett valve, and this gentlemans photos reflect the lack of fins.
Do you have one of these?
frank

 

[CAPT PETE]

Frank,

No, I don't have one of these yet but I am seriously considering it.

 

[cwa46]

FMarini

Thanks for your time. I am just confused and hoped you could help me. There still seems to be a substantial difference in theory between Escobal and your approach. I have no idea how both directions can be right and not enough knowledge to figure it out. Do you know of another source that might get me straighten out? I have a Mechanical Engineering degree and feel that I should be able to understand the theory. By the way, how do you measure skimmer efficiency?

 

[SciGuy2]

Frank,

Thank you for the excellent article. It goes a long way on showing why skimmers cost as much as they do. (It is a materials-intensive and time-consuming process developing a skimmer)

Has anyone considered recirculating the water in the lower box portion of the skimmer through the beckett foamer, and then adding a taller contact body (3'-4') like on the CC skimmers? I realize that your article was describing the development of a low profile sump skimmer, but for those of us with remote sumps or with the space for another piece of "furniture" it seems like the best of all possible worlds. Do you think PM has anything like this on the boards in the future?

Here's a quick sketch for discussion.

Thanks,
-Lee

P.S. Sorry about the blurry sketch.

 

[FMarini]

Sci-Guy:
Thanks for the comments.
Yes good skimmer are expensive, and they do require alot of tweaking to get just right.
The bullet box style skimmer was just the opposite of what you are asking for, however we did toy around w/ the idea of not only making a tall beckettheaded skimmer (its called the bulletXL), but also a recirculating one. AS you can see from the photo its similiar to the design you attached above. Water is drawn from the box and recirculated thru the becketthead.
I hope mike will allow me to post a picture of it. But if the photos don't show here is the link
http://precisionmarine.com/Bullet_S...irculating_Skimmer/recirculating_skimmer.html

Brilliant minds think alike. Buy the way if you want to see these two recirculating bullet skimmer in action. Visit FishRanch on Larkwood, in Houston, TX
frank