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DIY fuid bed filter


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I'm looking at making a fluidised bed filter, have got pvc parts and a philmac (black plastic irrigation style) backflow preventer thingo. I plan on using a pvc tube with end cap at one end and a threaded access cap at the other (ones with o-ring in them) to allow me to open the filter, maintain etc...

has anybody used these caps before - can they handle the pressure, without leaking?

does anyone have experience with the philmac valves - will i need to adjust / swap the spring? - is there any grease / other toxins i should be wary of?

also - a couple of the DIY sites on the internet mention using marbles / small stones to prevent backflow... has anybody done this, and does it work? if so, what size media.

If i already have a backflow preventer, is there any reason to still have teh media?

flowrates... does anyone know what is best for fbf?... and had another question... slipping my mind... oh - do you normally attach the fbf to an individual pump, or does anybody use a 'Y' split etc on the water return line?

any help appreciated ... lots

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lots of views, no replies - has anybody made one before? or have any ideas?

i found this thesis:

scholar.lib.vt.edu/theses/available/ etd-01042001-122834/unrestricted/ABSTRACT.pdf

that provides some excellent! information, but am still missing design specifics...

any help at all appreciated! really!

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The FBF should be connected to the OUTLET of only ONE filter (or filered Powerhead). Do not use a Y-connector as the water will just flow out the end with least resistance - the other end and not the FBF end!

It best works on filtered water and not just off of a straight powerhead outlet. You could add a sponge to the powerhead inlet to add filtering and aditional bacteria home.

I do not know about the one way valve thingy you are using... as it is for irrigation then it is not Food Grade and anything used to lubricate the valve may not be good for Living things.

With regards to the O-ring and end caps - There is really no added pressure when attaching the filter/pump. It should hold. It is not like you are presurising it like a storage tank... take a look at external canisters... some of these have what looks like minimal clamping of lids and small o-ring seals... and they work fine.

Also do a search here for FBF, Fluidised, Fluidized, Bed Filter, etc

There are a few topics regarding this already.

Also: I have seen on eBay some FBF for $40 and these normall are $80.

You might wanna check these out unless you are buidling a huge one for a fish room sump tank.

About what pump size... well that depends on you and how big the FBF is gonna be and how much media you have inside. As a guide you will need 1000 lt/hr minimum. the bigger the FBF the more lt/hr your pump will need.

Yeah people use rocks or marbles to help stop back flush when the power goes out... but this is more used to stop back flush blocking the pipes when power is restored and filter need to pump out the sand out from the blocked pipe. Is is not used to stop sand going back into the filter! Hopefully sand does not reach that far down the pipe. But to help stop this it is best to have the inlet pipe come down the side of the FBF to the base rather than just lay it horizontal from the Filter/Pump.

Some design incorporate 2 holes in the top - 1 for outlet and the other with an internal PVC pipe running to about 1cm from the bottom. This helps stop back sucking of sand... and a gew marbles will help.

BTW: I ran a gravel cleaner connected to a Via Aqua 1200 inlet as a FBF for about 2 weeks to see the FBF action of the gravel. I wanted to see what the gravel was doing at different angle of the gravel cleaner pipe... how much gravel it was sucking from the bottom at different angles and if any fish/catfish desided to venture in.

I found that this makesift FBF was quite fun to play with!

It was educational as well as it cleaned my gravel!

At any angle other than 90deg up, gravel entered on the high side and fell on the low side - depending on the dept of the gravel cleaner (G/C) in the sand and the angle of the G/C over time the level of gravel increased (24hr rose ~5cm till it stabailsed with gravel at entrance not being sucked in anymore). But if the G/C was touching the bottom of my tank then it was having trouble sucking up any new stones and the level did not rise.

The best angle was 80-90deg. At 90deg there was more turbulace but the G/C was flush on the bottom of the tank... so 8-85deg was good.

So was this experiment working... I don't know!

In terms if increasing Bateria growth and lowering bad stuff...My tank is not overstocked and tank levels were zero to start with... this was me just playing around.

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Nah did not build one.

The temptaion is always there to make one... But I found a decent one on eBay for $40 (did not buy it though)

So cost of making vs buying it for $40... I'd probably buy it for 1 tank.

If you need it for a multi tank sump setup then making it will be better.

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The philmac fitting uses a stainless spring that is quite safe to use for both fresh and marine systems. They are a terrific product, my one complaint is that they require a reasonable amount of flow pressure for them to open and stay open. For example some of the small pumps that I have used (3000l/hr) have not been able to open the valve.

The media at the bottom of the FBF is to allow it to start up with minimal problems after stoppage. The theory is that the incoming water enters a space with relatively large voids and can gain some momentum before hitting the more densly packed sand. The non return valve is ment to eliminate this problem but I still add the media as a precausion.

The size of pump is relative to the amount of sand that you are pushing through. I'd look at the recommendation on the websites that you have found.

The FBF is primarly a biological filter and has little effiecency in dealing with mechanical filtration. A lot of people believe they will become blocked if you do not prefilter the water. This is not true, the "gunk" just passes through the filter and back into the tank. You should always have some sort of mechanical filter to remove the "chunky" bits of waste and a prefilter on the pump or prior to the FBF is a very good idea.

The screw cap on the 100mm and 150mm PVC pipe will deal with the pressure. My only advise is that I would put a thin smear of silicone around the seal and tighten while it is still wet. This just provides a little bit of extra insurance, and is common advice when setting up sand filters for pools.

Hope that helps.


ps. I'm sure if you search the forum there will be other posts about building FBFs

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