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31-03-2019, 10:38 PM #1
Vortex filters - we're doing it wrong. Stairmand designs for pond sizes
This post has a background. Right now I'm designing and building my first pond.
As part of it, I'm looking to use approaches used in other parts of fishkeeping, and it seems I'm commiting heresy left right and centre. This post is about one of those heresies - vortex filters.
https://www.koiforum.uk/pond-constru...-contains.html
My hope is to use a vortex - which I'm going to call a cyclone from now on - as my main mechanical filtration. They are used in a lot of industries and they are *remarkably* efficient - easily 95% plus and often 99% plus - but this forum *hates* them. The general view is that they are not very efficient at all. That has been really confusing me - I've not been able to understand why a pretty universal wonder device is so bad when it comes to fish waste in water.
So... I've spent the last while looking at proper Cyclone design, and what I'm realised is that: Well designed cyclones are fantastic. But.... the average pond cyclone is so badly designed that they are probably only as useful as a settlement chamber... and so it's not suprising they have such a bad reputation. If anyone wants the references I've used, I'll post them as an edit.
Some basics:
Cyclones have been used for 100+ years filtering solids, liquids and gases. However, it wasn't until the 1950's and 1960's that the theory behind them was studied in detail by a guy called Stairmand, and he pretty much sorted out all the fundementals. In the mid-2000's there was another big push on the mathmatical modelling side of it, but it turns out that Stairmand pretty much cracked it back them - less than 1% additional efficiency has been found since then.
The key here is that whats considered a good design is not based on gut feel - it's very carefully studied with a lot of peer reviewed papers and PhD's behind them and also it's a very settled area. What comes below is me making a super high level summary, but it's all based on the Stairmand High Efficiency design - this is both simple and also almost the pinnacle of the designs available. It's also the most studied version as well.
How Cyclones work:
Water is injected at high speed right at the very edge of a circular drum and by doing so begins to spin and dramatically speeds up - causing an effect called Laminar Flow to form right near the surface of the drum. Anything which is more dense then the main fluid - in our case the fish poo - is subjected to G-forces of up to more than 20G in a good design - double what astronauts experience. This flings it outwards towards the edges, where it interacts with the laminar flow "tearing" against the walls edge. This causes it to slow rapidly and drop down the sides.
Critical elements of a cyclone:
- Speed of entry of the water
- Diameter of the top chamber
- Height of the vortex column
- Smoothness of the sides of the wall
The key thing here is that cyclones are:
- Absolutely rooted in science
- Delicate in their design - small changes can have *dramatic* effects on efficiency
Lets look at a common existing pond design:
Current vortex design.jpg
Key things to see here:
1) they are *massive* - they're bigger than industrial cyclones in large factories
2) They are very wide and pretty squat - many many times the diameter of the incoming and outgoing pipework
3) Flow coming in SORT of from the edge, but not really. Flow is coming in to the middle of the body rather than firing directly around the edge.
Heres an example of the internals of a common design
DIY cyclone.jpg
Water is not coming right at the edge. it's as wide as it is deep. And... critically..... the outflow pipe is getting in the way of the water column. This ruins the laminar flow and causes turbulance - this ruins the whole cyclone concept. What we're left with here is a settlement tank - NOT a cyclone.
Also note that it's not a smooth edge - it's full of edges. This means that the Laminar flow is unlikely to form at all - each vertex between the edges will cause turbulance which destroys the flow that makes the whole system work so efficiently
What does a high efficiency cyclone look like?
This is a Stairmand standard design - it will be at least 95% efficient and usually 98%+.
Cyclone isometric.jpg
- It's narrow - very narrow - only twice the diameter of the exit tube
- It's tall - but.... it's only around 5.5x the diameter of the exit pipe in height - so still smaller than the typical pond vortex
- Water is injected right on the edge of the chamber and flows directly around the edge, generating the Laminar flow.
- Critically - there is *nothing* in the water column. No pipes, no brushes, no protrusions, no edges - all totally smooth and plain.
Cyclone scaled for Pond use.
Every dimension is driven from the diameter of the exit pipe. In my case I'll be bringing this in directly from my bottom drain so it's sized for 4" diameter, and will be venting it back into another 4" pipe, so the design is based on a 4" design. If you want a different diameter then scale everything down proportionally from the diameter of your exit pipe.
Stairmair cyclone.jpg
For a cyclone for a pond rated for up to 40,000l/h , exiting to a 4" pipe, the total height is 32", and the diameter is 8" (internal). Compared to a traditional pond cyclone this is very different design.
Building it:
If you want a 2" output, then Amazon is your friend: https://www.amazon.co.uk/Commander-P...9XDVMZKXF5MGVV
That gives you the main vortex - it would need fabri-cobbling into a settlement tank to collect the waste and run it to your sump
I need a 4" version, so my first stop is going to be that nice guy at JBR ( thanks to this forum for the link to these guys - they're awesome) to see if he can put one together. If not, then I'll be making a fibreglass version - if I go down that route I'll make the forms re-usable - if anyone else wants to use them then just shout. The Next Door Neighbour is making noises that I should make it in Aluminium, but I'm still at the "filler and paint makes me the welder I ain't" stage with my welding so I don't think thats going to work.
Either way I'll post next steps over the next few days.
This post is mostly notes for myself, but hopefully someone else might find it useful.
Steve
Last edited by SlowSteve; 31-03-2019 at 11:04 PM.
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Frimley Koi keeper Thanked / Liked this Post
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01-04-2019, 07:03 AM #2
With an 8” diameter and the volume due to the need for speed of water movement don’t you think you’ll overflow?
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Frimley Koi keeper Thanked / Liked this Post
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01-04-2019, 07:36 AM #3
Hi,
No, it’s a sealed unit. Below the cyclone is a settling drum - not shown in the diagram - that’s what you feed to waste.
The speed of the water makes them entirely self cleaning.
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Frimley Koi keeper Thanked / Liked this Post
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01-04-2019, 07:40 AM #4
Waterco Multi Cyclone Centrifugal Filter For Koi Ponds MS 12
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F 221017033465
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01-04-2019, 08:55 AM #5
That filter is just under £250 or just under £290 if you want the stand as well so I would be very interested to see how you get on with this Steve.
I've looked at those as pre filters many a time but just wrote them off as I didn't understand them and also the price didn't help either.
Good luck.
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29-11-2022, 09:08 AM #6
Steve is this thread still up and running? Are you okay?? Did you get through the pandemic alright? Was just wondering how you got money with this? I had the crazy idea of a traffic cone inverted inside a drum. Not put it together yet. Trying to work out how tall they need to be etc. But currently working on vortex, feeding into wetland being my first choice for upcoming pond upgrade.
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29-11-2022, 10:37 AM #7Freddyboy the legend
"we are water keepers first"
Johnathan
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29-11-2022, 11:40 AM #8
Oh dear, I hope everything is OK. I definitely think he was on to something with the vortex system as effective mechanical filtration.
Best plants to remove Nitrate
pug has a very impressive veg filter on his pond, have a look at some of his his youtube videos....