European skimmers. What is it with them??

[agiacosa]

Alberto:

Mine is in transit. I've used Euro-Reef, Beckett type and air-stone driven. I'll let you know how it compares.

[tacocat]

I agree gas, but the foam was very dry, and the bubble size was small. The dry bubble plume, looked like it was a foot above the neck, and rising.

Also, you had posted that noone had ever seen the skimmer.

[stuart bertram]

Simple Skimmer Statistics

With skimmers it is very easy to compare them without even operating them simply by comparing the diameter of the opening on the riser tube.

A proper skimmer foam will only support itself, ie climb the riser tube if it has enough air behind it to drive it.

In simple terms - the larger the cross sectional area of the riser tube - the more air the skimmer is producing to drive the foam.

Diameters of the Deltec units are:-

AP1003/1004 - 5.5 inches
AP1006 - 7.5 inches

Note that some companies have a tapered tube which has a very small opening and therefore very little air.

---------------------------------------

The Deltec units sold in the States are totally different to the European models and are fitted with imperial fittings to match the pipework.

The main differences however are in the motors and Pinwheels.
For the 110V market special pin wheels had to be produced with special magnets to match the cycle speed and produce even more air as a concequence than their European counterparts.

The European models are not actually compatible with the voltage in the states and changing the motor for a standard US Eheim will not work as the pumps are machined to improve the water and air mixing. Plus the magnets are different.

Deltec spent about $10,000 on a piece of equipment that would exactly reproduce the voltage and cycles for the US market so that they could develop a product that performed as well or in this case better than the standard model.

After many decades of producing skimmers they have learned that to play in the big world, ( long term ) that you have to do things properly.

There will always be competition and alternative products which some people will like and some people will not.

Unless you try every type you will never know the pros and cons.

You pay your money and you take your chance.

Stuart

[npaden]

With skimmers it is very easy to compare them without even operating them simply by comparing the diameter of the opening on the riser tube.

That doesn't sound correct to me.

Based on your statement a euroreef CS12-6 EXT (72" tall, 12" diameter body, 4" diameter riser tube) would compare equally with a euroreef CS6-1 (20" tall, 6" diameter dody, 4" diameter riser tube).

Nevermind the fact that one is running 4 - 900gph pumps on recirc and the other is running a single 350gph pump that provides the input water as well as the air production.

I'm sorry but your simple skimmer statistics don't compute for me.

FWIW, Nathan

[Shoestring Reefer]

I agree with npaden-
Bubble size, dwell time, and several other factors are known to affect performance.

Also, for a given diameter, you can increase the water height in the skimmer (or reduce the height of the neck) and then you will still get foam with less air.

Also, a taller tube with a tapered (smaller) opening could skim just as well as a wider opening, but do it with a drier foam (and more "gunk" build-up).

[stuart bertram]

What you say may be true as I am not totally familiar with the Euroreef products and their performance - however:

In Europe there are many manufacturers who make tall column skimmers and sell on the longer contact time that it allows. Some even send the water up and down 2-3 times through concentric tubes which makes the column look very full of bubbles as you see the same ones 3 times.

These taller units have a much higher head of water above the pump and therefore require much more electrical power or more pumps to achieve the same amount of bubble generation at the greater head. Also once air is introduced into the impellor chamber then the head that the pump can drive is even lower.

Note that the larger Deltec Skimmers get fatter not higher for this reason.

It is therefore feasible that the 2 types produce the same amount of air although one has a much longer potential contact time. The fact that on the smaller model the pump is feeding the unit as well as producing air is irrelevant as it will still introduce the same amount of air unless the pipe work run is particularly restrictive.

The 4 inch diameter riser suggests that they are both comparable and producing about 700 – 1000 lts of air per hour if they both function efficiently.

The riser tube diameter is only a guide which you will find is a good indication of performance and not the only criteria. Watch my words

Regarding contact time.

A bubble of air can only hold a certain amount of waste and once loaded no matter how high the skimmer column is will not hold any more. This is why smaller bubbles with a larger surface area are better.

Tall skimmers look impressive though, so they must be better and that is why they sell.

There were some tests done by a scientific individual in Germany that showed that the air/water mixing at the Deltec pinwheel was so efficient that there was no difference in having a column height of 6 ft or 6 inches as the bubble was loaded at the pinwheel.

Regardless of the efficiency or not of the mixing there is also another reason for the column of water and that is to slow down the turbulent water movement that comes out of the pump so that it can rise to the opening and form a stable foam without being dragged back into the water column. It also allows the bubbles to rise so that bubble free water can be introduced back into the tank.

There was a mistake on the last message. The specs should have been:

AP1004 - 6.3� diameter riser tube – 2200 -2400 lts air/hr – using 166W of power.
AP1006 – 7.5� diameter riser tube – 3300 – 3600 lts air/hr – using 249W of power.

Re
Also, a taller tube with a tapered (smaller) opening could skim just as well as a wider opening, but do it with a drier foam (and more "gunk" build-up).

This is also true of course but the diameter comparison assumes that all proper skimmers are all fitted with a long neck to collect a proper dry waste which is the colour of coffee and smells like something has crawled into the cup and died overnight.

If you are having to run the water level in the riser tube then the neck is too wide for the amount of air that the pumps can produce.

Stuart

PS the picture on page 13 shows a very wet foam or fizz and not a skimmate that you would want to collect in your cup unless it is part of your water change regime. The bubble size is good as would be expected from a pin wheel skimmer.

[Shoestring Reefer]

What skimmer are you rinning on your tank, Stuart.

[agiacosa]

Stuart,

The image on page 13 was done without the skimmer collection cup and meant to depict bubble size and quantity. Certainly you'd tune the skimmer down to obtain the appropriate skimmate being collected.

[npaden]

These taller units have a much higher head of water above the pump and therefore require much more electrical power or more pumps to achieve the same amount of bubble generation at the greater head. Also once air is introduced into the impellor chamber then the head that the pump can drive is even lower.

If the pumps are on recirculation they are not running at any vertical head loss. They are strictly recirculating the water within the column adding air from the outside but recirculating the same water.

The 4 inch diameter riser suggests that they are both comparable and producing about 700 – 1000 lts of air per hour if they both function efficiently.

Again I will have to disagree with you here. The riser tube is not an accurate depiction of the amount of air that a skimmer is capable of handling.

There were some tests done by a scientific individual in Germany that showed that the air/water mixing at the Deltec pinwheel was so efficient that there was no difference in having a column height of 6 ft or 6 inches as the bubble was loaded at the pinwheel.

Doesn't this disagree with your statement for why the Deltecs are so good because they are short and fat? I thought you said "These taller units have a much higher head of water above the pump and therefore require much more electrical power or more pumps to achieve the same amount of bubble generation at the greater head."

FWIW, Nathan

[stuart bertram]

Quote
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If the pumps are on recirculation they are not running at any vertical head loss. They are strictly recirculating the water within the column adding air from the outside but recirculating the same water.
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This is not entirely true.

You are right that the water has no head loss however for the air to enter the venturi it has to fight against the head of water.

Quote
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The riser tube is not an accurate depiction of the amount of air that a skimmer is capable of handling.
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It is our experience that this is the case - try it and see.

Quote
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Doesn't this disagree with your statement for why the Deltecs are so good because they are short and fat? I thought you said "These taller units have a much higher head of water above the pump and therefore require much more electrical power or more pumps to achieve the same amount of bubble generation at the greater head."

The reason why they are good is through patented design and extensive testing.

The reason for the shorter body rather than the tall one is to achieve the same dwell time without the extra head pressure to fight against as explained. Extra height costs extra energy to produce the same result.

Stuart

[ktani]

I love this thread, great information.

As a secondary yet important issue is service. I saw and was at the Deltec booth at MACNA and was impressed with their equipment. It was touted that David Saxby and Steve Weast both had them. I highly respect both and took that into consideration.

One further issue is if something broke or needed replacement. Setting up a couple of larger tanks, my hope was the rep would have spent some time chatting with me regarding their equipment, however he made no effort and after waiting around for a while I left. Came back probably 4 or more times seeing if I could get some of his time to discuss the equipment but with no luck. If I am buying and cannot get his time, what would it be like if I needed support or parts? That is what has crossed Deltec off my list.

So now, it is down to Schuran, Bubble King and RK2.

Personally I agree with Nathan and Mike, that bubble size, dwell time and such also have merit. Electricity cost is important too, but given a choice between higher electricity cost and less effective skimming, I would choose the former. If both can be had, that would be better as in the Bubble King.

Kip

[1diverdown]

hi Kip,

you have a pm

Doug

[Shoestring Reefer]

Originally posted by stuart bertram
Quote
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If the pumps are on recirculation they are not running at any vertical head loss. They are strictly recirculating the water within the column adding air from the outside but recirculating the same water.
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This is not entirely true.

You are right that the water has no head loss however for the air to enter the venturi it has to fight against the head of water.

Any pumps (including needlewheel impeller pumps) with the venturi on the pump suction don't have that problem when pumping into a skimmer. A recirc pump would only be affected by that if the venturi was near the bottom of the skimmer. And, a properly-matched venturi/s would not have that problem regardless of the head.

Venturies work in power systems in excess of 1000 psi, and still have little flow restriction, so an extra foot of skimmer height should be no problem. If you're frankiensteining something together in the basement, that may be a different story.

[stuart bertram]

If you take the same pump arrangement and increase the head above it then you will see a reduction in the air inlet volume.

Remember that a venturi works by creating a low pressure region behind a restricted section in the main flow.

The pressure increases in the restricted section where the velocity increases and then decreases once the pipe opens up. This expansion creates a low pressure zone which draws in the air.

The higher the head of water above the venturi then the harder it is to create a low pressure zone to draw in the same amount of air.

Like a water manometer the pressure at the venturi still has to overcome the tendency of the airline to fill with water which is what would happen if the venturi pressure was removed.

Undoubedly it is possible to create a venturi pressure of 1000 psi but at what cost in wattage. certainly more than the 41.5 watts per pump on a Deltec eheim.

Most venturis on skimmers are at the bottom as this is where the air is drawn from.
If your skimmer is blowing in air half way up then it is wasting half the tube as it is not doing anything.

Stuart

[bernie lyons]

Stuart , the pinwheels that deltec uses , are they manufactured by deltec ? I have compared them to another german brand skimmer and they both look very similar.
regards
bernie

[dgasmd]

Originally posted by stuart bertram
Like a water manometer the pressure at the venturi still has to overcome the tendency of the airline to fill with water which is what would happen if the venturi pressure was removed.
Stuart

Stuart:

Sorry to correct you here, but the pressure on the wall of a pipe with high velocity of a fluid is the lowest and therefore does not have a tendency to fill the tube. That is exactly the physical reason why venturis and eductors work. You increase velocity so much that you create a lower pressure area at the walls of the tube creating a draw of air from the higher pressure atmospheric are outside the pipe. You can find this in any simple physics book.

The reasoning of a wide riser tube allowing more air to come out is not so strong either. Look at the size of the air tubing getting the air ito the skimmer in the first place. It is a 1/4" or so tubing, so why would you require 8"across to allow that same volume of air going through the smaller tube to come out? It makes no sense. I do think that the larger riser tubes likely aid in the formation of dryer foam regardless of the tuning of the skimmer because it has a larger area for foam to accumulate in and dry as it spills over. A narrower rising tube would force the foam to spill over much quicker before it has a lot of time to dry up.

I see a lot of people putting a very high regard for the Schuran skimmers, but that is another skimmer that I can safely say less than a handfull have seen in action in the US. Very uncommon in Europe too. Actually, most people I know that have seen them in action were pretty unimpressed with their performance. Very pretty skimmers, but pretty doesn't do much for performance. RK2 and sanders skimmers are pretty much there with the Schurams as far as performance and efficiency.

[SHARKSRME]

I am still not convinced that the "euro" skimmers are better. I've been around this hobby for the past few years working in a high end pet shop and now in the wholesale end of things. I've seen euroreefs, deltecs, remoras, Rk2s, and many more. I highly doubt I can find a more efficient skimmer than the one I am currently using. I have a MRC skimmer with quad becketts. Now your probably thinking I must be using a million watts to power it. Not even close. I use a pump thats rated at 367 watts max. I do think the mrc's should have longer injector riser tubes though.

http://www-2.cs.cmu.edu/~cap/raid/skimmers/thoughts/

These images were taken before I modified it slightly and had it dialed in correctly. I now get better performance. I am going to install a flow meter so I can see the scfh. I wouldn't be shocked if I was getting 800scfh +.

[stuart bertram]

Originally posted by dgasmd
Stuart:

Sorry to correct you here, but the pressure on the wall of a pipe with high velocity of a fluid is the lowest and therefore does not have a tendency to fill the tube. That is exactly the physical reason why venturis and eductors work. You increase velocity so much that you create a lower pressure area at the walls of the tube creating a draw of air from the higher pressure atmospheric are outside the pipe. You can find this in any simple physics book.

I have just worked out how to do this quote thing. Fantastic.


We digress but I beg to differ with this.
Anyone who has made their own venturi would tell you that if you put a side air line into the wall of a high velocity section of pipe then what will happen is you will get a jet of water not suction.
There will be fluid pressure differences between the wall and centre of the pipe but not enough to create an efficient venturi unless the velocity is very high which costs energy.

In the high velocity section of a venturi the water is at a higher pressure as it is compressed by the pump to go through the restriction. The smaller the restriction the higher the pressure to force water through it and the higher the relative running cost to achieve it.
The high velocity pipe or restricted section must then open out into a wider area of pipe which allows the water to try to expand again to its natural pressure. ( ie the pressure that the water would naturally be at at that depth, flow and temperature).

As the water is still flowing through a pipe where the only openings into it are from the open end, (which is at even lower pressure) and the venturi inlet, then the pressure is balanced by drawing air in through this.
The higher the water flow the higher the static pressure at the venturi and the more air that is drawn in.

Try this out with the following link.

http://www.ce.utexas.edu/prof/KINNAS...i/venturi.html

The venturi and air volume is only part of the story as the bubbles provided by this are comparitively large. The Deltec pin wheel then smashes these up into fine bubbles with a much larger surface area to react.

The pinwheel must also provide flow and the more air that is introduced over it the less efficient it is as a pump and so the velocity through the venturi goes down and there is less air.

The difference between the pin wheel designs is therefore critical to the balance between air and water mixing/entrainment.
So to answer Bernies question - no they are not all the same and are made to a specific Deltec design which changes between models and voltages.


The reasoning of a wide riser tube allowing more air to come out is not so strong either. Look at the size of the air tubing getting the air ito the skimmer in the first place. It is a 1/4" or so tubing, so why would you require 8"across to allow that same volume of air going through the smaller tube to come out? It makes no sense. I do think that the larger riser tubes likely aid in the formation of dryer foam regardless of the tuning of the skimmer because it has a larger area for foam to accumulate in and dry as it spills over. A narrower rising tube would force the foam to spill over much quicker before it has a lot of time to dry up.

The air coming down the inlet pipe is air and not foam and is therefore obviously not the same.

A foam has properties somewhere between a liquid and a solid and is capable of supporting its own weight depending on its thickness (non technical term). This is why it can climb the neck of the skimmer.
The bubbles in the foam are constantly bursting and changing back into a liquid which flows back down the neck. In order to climb high there must be more foam in a stable state than that which is flowing back down. The stable foam is produced by waste and air and both must be present to climb the cup.

If you therefore take a fixed mass of foam which is constantly changing it will reach a head which is dependant on the diameter of the container in which it is held. If you double the area of the container you half the head.

Assuming that we all collect skimmate at the same degree of dryness which can obviously be altered by changing the water level then the original statement of:

"With skimmers it is very easy to compare them without even operating them simply by comparing the diameter of the opening on the riser tube"

This still holds true.

The photos on the previous message show a skimmer with a very long riser tube which is obviously skimming very efficiently and removing a very dark dry waste.
However the fatty/protien deposits that are collecting low down on the riser tube will be having a massive negative effect on the ability of the foam to climb and will significantly reduce the amount of waste collected in the cup as the bubbles burst and grow the protein layer rather than collecting in the cup.

This looks an excellent skimmer but I would say that the riser tube should be wider to force the foam to climb without depositing so much on the sides.

An exception to the general rule in this case perhaps but I still stand by the priciple.

[stuart bertram]

Obviously I have not worked out how to use the quote bit then

Stuart

[RGibson]

SHARKSRME-you need to take a look at the post 280 gallon tank project has begun.Chech page 25-26-27.

[SHARKSRME]

Very Interesting. Maybe I should take off my needlevalves and install an extremely large flow meter on the end...something in the 1inch range! Although it would get crap built upon it .....hmmmm

[stuart bertram]

To get accurate readings of airflow you need to use a vacuum airflow meter which is calibrated to the pressure that is produced by a pump venturi.

Standard pressure type airflow meters do not give accurate readings.

Stuart

[npaden]

stuart, I think you are confusing even yourself. If a pump is strictly recirculating the water in the skimmer there is no head pressure and water flow would be the same velocity whether the skimmer body was 100 feet tall or 10 feet tall. The pump is not affected by the height of the skimmer because the pump is recirculating the water. The venturi creates a low pressure and causes suction of air based on the velocity of the water flowing through the venturi. This is based on the velocity of the water. Period.

FWIW, Nathan

[Shoestring Reefer]

To clear up some things that have been said:
- A venturi works by creating a low pressure at the THROAT of the venturi. Any low pressure downstream of the venturi is an unfortunate side effect. Venturis work based on the conservation of energy, where [energy = pressure X velocity]. When velocity increases through the throat of the venturi, the pressure drops to conserve total energy. Venturis are used because their gradual contraction and re-expansion cause relatively little reduction in downstream pressure. In fact, with a proper venturi, you will NOT be able to draw any air into the system downstream of the throat.

IF you have a "venturi" with the air inlet downstream of the throat, you really just have a flow restriction that reduces the downstream pressure. You can do the same with a valve. For a cheap and easy alternative, Maby someone could try to make an orifice: join two pieces of PVC with a slip X slip fitting, and stick a plastic washer (or some other non-corrosive object) in the fitting - the two pipes will hold it in place. You may need to file down the outside of the end of the pipe to make it hold the orifice snugly. Or make a "venturi" that does the same thing with twice the work and a pile of cut-up fittings. IMO, the "Squished Tee" venturi is a great idea.

- A pump draws LESS power when it's flow is restricted. You can look at any commercial/industrial pump curve to see the power requirement drop as pump head increases and flow decreases. It's an easy mistake to make; I determine pump performance criterie (among other things) for a living, and I still make that mistake because it's counter-intuitive IMO. Another RC member explained how at low flows, the impeller starts to exceed the sheer capacity of the fluid (ie, water) and begins to transfer less energy to the water.

-Increasing the line pressure WILL increase the pressure in a venturi's throat for a given flow rate, but there are several ways to design around this (including component selection and physical design); besides, the skimmers obviously have no problens getting enough air to skim, so the point is moo (like a cow's opinion, it doesn't matter.)

[stuart bertram]

Originally posted by npaden
stuart, I think you are confusing even yourself. If a pump is strictly recirculating the water in the skimmer there is no head pressure and water flow would be the same velocity whether the skimmer body was 100 feet tall or 10 feet tall. The pump is not affected by the height of the skimmer because the pump is recirculating the water. The venturi creates a low pressure and causes suction of air based on the velocity of the water flowing through the venturi. This is based on the velocity of the water. Period.

FWIW, Nathan

Lets take this to its nth degree.

Are you saying that if you have a standard venturi skimmer pump running at the bottom of the ocean 200ft down that it would take no more energy or velocity to draw air down to it against the pressure of the water trying to go up the pipe than it would at the surface. - I think not.

Also
When you turn off the pump the water flows up the air pipe to reach its own level. What do you think is stopping this happening when the venturi is in operation - the force created by the venturi.

If you put your mouth on the end of the air pipe and blow when it is switched off do you think you will have to blow harder if the pump is 1 ft under water or 6 ft.

The venturi obviously has to work harder at a greater depth as ir has a further 5 ft of water guage WG to overcome.

Stuart