bottleneck

[andycook]

Hi;

Most skimmers I have seen have a narrow neck just before the collection cup. Why design it with the bottleneck? Would it not be more effecient in terms of energy and "gunk" collection to remove the bottleneck and have the tube extending into the collector cup be the same size as the tube leading up to it? Thanks.

-Andy

 

[FMarini]

Hi Andy:
great question, and one that i can answer.
So this decrease in diameter is actually a function of getting the foam up and out of the skimmer is a efficent manner. In that this linear decrease in diameter forces the air to accelerate (as the size of the tube decreases in diameter) which allows a more forceful ejection of foam.
The second thing the bottleneck does is prolly the main reason why manufacturere use them is they are gradual foam supports. What I'm trying to say here is that this linear reduction in size allow the foam to be supported as it accumulated, and the higher up the neck it goes the more support it recieves since the neck is narrowing.
So combine these two functions, greater air velocity and increased foam support and you can see why these are useful.
One caveat to this whole process, is that constructing these bottle necks is difficult, usually they are created by vaccum molding or injection molding, and this will really bring up the cost.

Do you need this bottleneck? No not really, many excellent skimmers do not have them, and the main reason is that these top skimmer move sufficent amounts of air, to not require an increased velocity to shoot foam over the top. Would a top skimmer benefit from using a bottle neck. IMO yes.
Does this help?
frank

 

[andycook]

bottleneck

Hi Frank;

Thanks, I do follow. The support and airspeed were not things I had thought of. Do you think those benefits require a gradual bottleneck (a funnel) or are they present in the designs where the column goes from a large to a not as large tube abruptly? It seems to me that the models with the abrupt bottlenecks waste energy.

I'm working on building a skimmer and have found more unknowns than knowns. I hope Precision Marine understands that imitation is a form of flattery.

-Andy

 

[FMarini]

Andy;
I follow your idea as well. So when we were testing the neck desings of the bullet we used both non reduced necks, linearly reduced necks, and funnel shaped (cones). In all tests we performed the cones always performed better, even in the high speed skimmer where we were moving tremendous amounts of water and air, the cones allow a better air flow, more forceful foam ejection, better foam support, and overall better drying. Alas, money gets involved here, cones were much too expensive to include in a skimmer, and the compromise were the linear reductions(eg. a 4" neck on a 6" diameter skimmer, etc). AS far as manufacturing goes the stright up and down -no reduction design is the easist to build, and again depending on the amount of air your moving it works fine. The higher the air flow the betteer it works, if your designing a neck on a slow flow skimmer then the linear or cone shaped necks offer better dynamics. Also consider the use of foam supports and maximum venting of the air to increase foam ejection.
Lastly, the question really is? is a neck and collection cup even requird? I am of the opinion for the high flow, high air movement skimmers that collection cups are useless, and are nothing more than restrictions to proper collection. I would suggest that a tapered collecting top which vents via a large opening fitting directly into a waste collector might be more than sufficient. The only concern i have is that the taper be sufficent to allow foam support and increase the air acceleration upward.
Collection cups IMO are 1950's technology never updated.

Right.... about the PM copy. If you are gonna build another beckett skimmer copy, may i suggest you build something along the lines of the bulletXL or the aerofoamer. AS I mentioned in my Apr REEFKEEPING column tangential flow injection is the better way to use a beckett as it requires less pump, and is more forgiving. You can easily power a 24" tall beckett skimmer w/ a mag18.
My opinion
frank

 

[dsb1829]

Good question Andy,

I actually ordered a couple of funnels from US plastics for just such an application. I am building a DIY becket skimmer that will utilize greater contact time, a smaller pump, and off the shelf components. I already knew about the advantages of such a transition, but have not heard it all laid out in one place. Thanks for the confirmation Dr. Marini.

FWIW the large throat funnels that they sell are very poorly manufactured. Best bet is to stick with standard funnel and enlarge the throat to an appropriate cpvc or acrylic size.

ttt...

 

[andycook]

I thought the Paris article advocated no bottleneck? It was in the "suggestions" section at the end of the article.

The decision, for me, to build in a funnel vs no funnel is made by the size/height of the tube being used in the skimmer. Shorter/less wide tubes, in my opinion, benefit more from no funnel becuase there is less loss of energy while taller/wider tubes benefit, again in my opinion, more from the funnel because of the support, etc. Basically if the tube is 4" or less I suggest building without the funnel and if the tube is 4" or more I suggest building with the funnel.

I plan on trying the same 4"W x 24" tall tube with and without a funnel.

 

[7thheaven]

Hi~
FMarini...
I read your article several times and your article is so great & Perfect. I have many information from your article...
thank you...

In Korea, Because the cost of Electricity is higher than America,
Many People modified skimmer,Euroreef ,Aeroformer, macro(from china) etc..
they remove a pump and Use 2~4 woodstone , 15watt AirPump....
It reduced heat of pump and, relatively cost of electricity...
(of course they cost wood stone.... )
It is like a new fashion and many people have satisfied that result...

And My question is about riser( Is term correct?)
1. In case of Using woodstone, which is more efficient, the length of
riser short or long? I think it depends on the amount of air or
flow...

2. If the length of riser is same, which is more efficient, the diameter is narrow or not? also it depends on air or water flow?

3. you said "the compromise were the linear reductions(eg. a 4" neck on a 6" diameter skimmer, etc)" .can wood stone use in 4" nect on a 6" diameter skimmer ? and the efficient number and size of woodstone?

I don't know you understand my question because my English is
not good..(sorry~)

 

[FMarini]

Hey:
No worries about your english, my spelling is terrible.
But first.... your soccer team is amazingly quick. I haven't seen athletes in such aerobic conditon.

1. In case of Using woodstone, which is more efficient, the length of
riser short or long? I think it depends on the amount of air or
flow...
great question, in my experience longer risers allow the foam to dry longer and often times there is a fine line between too long a dryin time and not enuf. i would say in a skimmer which moves tremendous amounts of air (like a beckettheaded skimmer) longer (taller) risers allow good firm foam support and allows more water to be removed from the foam. However if you look at most air powered skimmer the riser tends to be short or should i say not very tall. What is the right height? I can't say, but i would tell you in general you'll want a short riser.

2. If the length of riser is same, which is more efficient, the diameter is narrow or not? also it depends on air or water flow?
your right, it will depend on the amount of air flow, but i think we can address easily. A narrower riser will accelerate the same amount of air over that a wider riser tube. The concern is that too narrow a neck and you restrict the proper movement of foam and not the air. So there is some sort of compromise. I would say on a 6" diameter skimmer a 3-4" diamter riser is sufficient. On a 4" diameter skimmer a 2-3"diameter neck, etc

3.you said "the compromise were the linear reductions(eg. a 4" neck on a 6" diameter skimmer, etc)" .can wood stone use in 4" nect on a 6" diameter skimmer ? and the efficient number and size of woodstone?
if you read and believe the information from Al theil then for every 4" of diameter you'll need 4 air stones, so a 6" diameter skimmer would require approx 6 airstone to maintain maximum air. I however have seen some very effective CC skimmer using 4-4" airstone. The key as you can imagine is the air, if you can push more air thru the stones then it willwork better. i have seen these tetratec deep airpumps work very effectively on less than 36" tall skimmer, above this hieght, you'll need more specialized air pumps. As far as the compromise for the riser. i would suggest to you that a traditional (linear) step down in riser size will work, as will a funnel (geometric reduction). I'm not sure which is easier for you to make.

Does this answer your questions?
frank

 

[7thheaven]

about air pump

about air pump

Thank you for your kindness reply...

At First...
you know our team win against Italy....
Did you see that?
wow....Incredible and unbelivable....wow....
It is like a movie I've never seen before....
wow.....

I understand many of them about skimmer for your help....

and another question....

if 4" diameter-> four woodstone, how big airpump wattage?
in our contry, in general, they use 15 watt airpump....I am not
sure they modified Euroreef with 2 woodstone_15watt air pump
and I think they are satisfied very much...

is it proper to use in skimmer?