Overflow Box (prefilter auto syphon) design

[Andrea_Aust]

I've started my system with the MariSys 240 and am ready to upgrade my sump/refugium/skimmer etc. Slight problem - the overflow box that comes with the MariSys has proven rather limiting in terms of its size compared to other brands.

I also don't trust the 'slot' style OFB (MariSys / CPR / ReefOctopus etc) and I think while I run the small pump on the bleeder, I'd much prefer to go with a good U tube design.

The one I have decided on (based on feedback and general positive comments) has been the LifeReef design.

This is the link to the LifeReef website - product pages will outline their pre-filter boxes.
http://www.lifereef.com/frame.html

I have read nothing but good reports on these OFB's. I will contact them to see if they can make me this one but I'm thinking the shipping to Australia is going to be a killer and then what if something doesn't fit? I'm having nightmares thinking about all the drama I could encounter dealing with a company on the other side of the world.

I'm pretty sure I could get it fabricated here. To me the idea looks pretty straight forward in terms of acrylic work.

----

When I built my rockwall (made with black foam / dried coral rock etc) I was working around the MariSys inner box not really thinking I would ever want to replace it.

As you can kinda see in the pic below - its all pretty tight room wise. It's ugly too

http://i477.photobucket.com/albums/rr135/MadDogNoz/DSCF5626.jpg

. I've tried to put something together that works with the size limitations - more reliable and not so intrusive visually.

http://i477.photobucket.com/albums/rr135/MadDogNoz/AndreasOverflowDesign.jpg

I also wanted to add a lid/cover to slow some algae growth in the syphon tube. If its too noisy, there's a good DIY site that has a silencer for these OFB's.

The problem I have is, I'm not sure if I've left out some crucial detail in terms of 'workability'. I get the basic principle of automatic syphon and in theory, the U tube should remain full. I don't know if the divider in the outer box needs to be set at any specific height in relation to the U tube.

Likewise in terms of the inner box ---- (there is an adustable butterfly nut to set the height but other than that, is this the only method of setting the water level inside the tank?

As you can see, I've drawn in the absolute maximum water level and the heights at which my tank trim comes up.

Anyone with any thoughts? Is there anything glaring that raises a red flag?

[Andrea_Aust]

bump

[der_wille_zur_macht]

Looks like a solid design. You have the baffle in the outer box to prevent siphon break if the return pump gets turned off, which is good.

Regarding the butterfly nut you have for height adjustment of the inner box - I would suggest making the inner box a separate assembly. Then, have the "lip" from the outer box extend down into the tank, with two slots, such that the inner box can slide up and down and be secured with the two nuts - if that makes sense.

Also, I would 100% urge you to do a silent standpipe design from the start - durso if you have room, or stockman.

And, considering sizing of different components, one of the keys to preventing bubble buildup in the u-tube - which can lead to siphon break - is running the system as close to the capacity of the u-tube as you can. IMHO, the easiest way to do this is to use a u-tube sized appropriately for your flow requirements, but use a bulkhead for the standpipe that's a size or two larger than you think you need (i.e. go up to 1.5" if you think you need 1"). That way, the standpipe will be well under it's capacity, which will help ensure quiet and reliable operation, while the u-tube will have a fairly high velocity for it's size, which will help ensure bubbles don't build up in it.

Also, keep that little aqua-lifter style pump you have to prevent siphon break, and find a way to use it with your u-tube. Either run a piece of airline up inside the u-tube to it's highest point, or put a nippe at the top of the u-tube.

[Andrea_Aust]

Thank you so much for your tips. I've been tinkering a little (see update pic)

http://i477.photobucket.com/albums/rr135/MadDogNoz/AndreasOverflowDesign-1.jpg

I've made the slots shorter to ensure more water remains in the inner box - someone mentioned that this may help and my inner box is smaller than most commercial ones so thought this would be a wise move.

The adjustment you suggested makes sense ... easy enough thanks!

Ditto on the silencer -- have saved some DIY plans that should make this possible.

Was planning on keeping the small pump but really...most of my siphon issues with the MariSys OFB have been because (well first the C channel design) but also because the pump tends to block up easily so its not super reliable. If I can keep the airlines out of the light, that may help because mostly its the algae inside the line that causes suction issues with the pump.

The black cap is now a cap that will meet with the inner box and sit over the outer to deal with algae.

Do you think it matters if the Utube is cut at different levels? I just thought because I am so limited height wise in the inner box, is there any reason why I can't have it longer in the outer (again trying to make sure air doesn't get in there)?

I've gone with 1.25" BSP bulkhead ... will see whether I can fit a 1.5" ...

The tube size vs flow is what I am not 100% clear on. Based on LifeReef design this size allows for 600g/h ... my pump should move about 450-500G but that's not taking into account the head height losses. I need to be a little careful too that I don't have too much flow through the refugium because its only a small 18" square tank.

This is where it gets a little scary ... matching it all up. :mad:

[Snakebyt]

make sure you have room in your outer box to put in a durso or other type of silencer, you will defenatly want one

[der_wille_zur_macht]

Don't worry about 100% matching flow rates and such. Your u-tube should be in the right neighborhood, and a 1.25" drain bulkhead will accomodate a standpipe that should surely handle your flow. IMHO, that's right where you want to be - a little excess capacity in your standpipe. If it turns out that the return pump is too strong, just put a valve on it's output and turn it down a bit.

You can have the U tube longer in the outer box, but the baffle "protecting" it from the rest of the outer box needs to be more or less above both ends of the tube - the end right next to it in the outer box, and the end in the inner box. Otherwise, water will drain down to the point that the siphon will break. Of course, this baffle needs to be shorter than your target water level during operation, or else the design won't work.

[Andrea_Aust]

<a href=showthread.php?s=&postid=15499468#post15499468 target=_blank>Originally posted</a> by der_wille_zur_macht
Don't worry about 100% matching flow rates and such. Your u-tube should be in the right neighborhood, and a 1.25" drain bulkhead will accomodate a standpipe that should surely handle your flow. IMHO, that's right where you want to be - a little excess capacity in your standpipe. If it turns out that the return pump is too strong, just put a valve on it's output and turn it down a bit.

I've been reading on WetWebMedia that its a good idea to run 2 U tubes instead of one - an added measure for safety should one block. But then I was worried that with an extra tube, the flow would then need to be divided between then right? I would worry that this may cause air bubbles accumulating in one or both tubes.

Just wonder if you could offer me your thoughts on this? I suppose I could use smaller dia tubes? Not sure whether they wouldn't foul up too quickly being a small diameter....ie - more chance of drama re blocking up?

You can have the U tube longer in the outer box, but the baffle "protecting" it from the rest of the outer box needs to be more or less above both ends of the tube - the end right next to it in the outer box, and the end in the inner box. Otherwise, water will drain down to the point that the siphon will break. Of course, this baffle needs to be shorter than your target water level during operation, or else the design won't work.

Ahhh ... that's a handy piece of advise! I raised that baffle not realising it is getting very close to my tank operating water level.

If I have the room, I'll try to squeeze in a 1.5" ...