Question about HOB overflow box
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hoffmeyerz
Active Member
The interior overflow box in the tank needs to be deep enough to accommodate different flow rates, lower flow will have a low water level in the box and as the flow increases so will the level. The pre-filter box on the outside needs to be lower than the overflow box to create a siphon so it's depth is related to the overflow box. They are rated for the flow they can handle. If my memory is right I believe my Lifereef overflow box is rated for a maximum flow rate of 600gph.
Thanks for your answer!
I thought that the flow rate of the outside box depends on the size of drain pipe and not the depth of the box itself. The volume of the box is too small anyway and it's gravity drain, as the water pressure would be near 0, wether it was 9'' or 5'' deep. Am I missing something?
Well I don't know anything about why but I run 2 eshopps hob overflows and if they were 4 or 5 inches deep I would have water all over the floor. The working water level in one is 4 inches and the other is 5 inches deep.
vlangel
Seahorse whisperer
Yes, I also have an Eshopps PF 800 and it is deep just like the OP has observed. But I believe it is for the reason that exnisstech has pointed out in his/her reply. The inside box is the size that it needs to be so that the U-tube can be fully filled. If that inside box is too small to have enough water and flow to fill the U-tube, then bubbles can build up in the U-tube and eventually the syphon can be lost which is catastrophic. I am sure Eshopps has designed the inside box to be the right size to match the recommended flow of the given model. I am very pleased with my overflow box as I have used Eshopps for decades without an incident of water overflowing my tank.
Thank you all for your help!
So the flow rate of the return pump is an important factor as well.
The reason I'm asking is because I'm DIYing my HOB Herbie overflow to add a sump and I'm trying to figure out some things.
My tank is only 60L, the weir of the overflow (inside box) has a max flow rate of about 2,200 L/h and my DC return pump is rated between 360 and 1200 L/h. Main drain pipe is 1'', so it has a max flow rate (gravity drain) of 2,250 L\h. The emergency standpipe is also 1''. I already have an acrylic container that's 10'' long x 3.5'' wide x 7'' tall. I guess it would be OK to use it as an outside box, since the return pump is about half of the capacity of the drain pipe. Correct?
So the flow rate of the return pump is an important factor as well.
The reason I'm asking is because I'm DIYing my HOB Herbie overflow to add a sump and I'm trying to figure out some things.
My tank is only 60L, the weir of the overflow (inside box) has a max flow rate of about 2,200 L/h and my DC return pump is rated between 360 and 1200 L/h. Main drain pipe is 1'', so it has a max flow rate (gravity drain) of 2,250 L\h. The emergency standpipe is also 1''. I already have an acrylic container that's 10'' long x 3.5'' wide x 7'' tall. I guess it would be OK to use it as an outside box, since the return pump is about half of the capacity of the drain pipe. Correct?
vlangel
Seahorse whisperer
I calculated how much flow was coming into my tank. I bought an overflow box to closely match that. However to further my chances of perfectly tuning into the flow to fill the U-tube, I bought a variable speed return pump and tuned it in perfectly like that.
hoffmeyerz
Active Member
You are correct in regards to the outer pre-filter box, it is not as impacted by the flow rate coming in. That can be controlled by the diameter of the drain pipe and use of a gate valve on the drain line. The inside overflow box can only handle so much water being dumped into it, lower flow in means lower water level in the box, more flow and the water level in the box rises. At a certain flow rate the water level in the box will reach the weir and the box can't move anymore water outside the tank.
Manufacturers will make the overflow box to accommodate certain flow rates for different size tanks and user's preferences. I run my pump at a flow rate that keeps the level in my overflow box about half way, that's just where the sweet spot for my tank seems to be.
Keeping bubbles out of the siphon tube is important as a few people mentioned, if a bubble grows large enough it will break the siphon and possibly create a flood.
Thank you all. Great info!
So, here's what I'll do:
1) Add a gate valve to the main drain pipe (so that I can adjust the drain flow)
2) Drill an air vent on the highest point of the U-tube(s) (and attach an air line that will end in the outside box, next to the lowest end of the U-tube). I have to check this, because I've read somewhere that enough flow will push any bubbles out of the U-tube.
3) Make sure that both ends of the U-tube(s) are always under water. Especially that in the outside box, that it's lower than the drain pipe (so that it maintains siphon).
4) Make the inside box height adjustable, so that I can adjust the water level in the DT.
I think we've covered all bases.
So, here's what I'll do:
1) Add a gate valve to the main drain pipe (so that I can adjust the drain flow)
2) Drill an air vent on the highest point of the U-tube(s) (and attach an air line that will end in the outside box, next to the lowest end of the U-tube). I have to check this, because I've read somewhere that enough flow will push any bubbles out of the U-tube.
3) Make sure that both ends of the U-tube(s) are always under water. Especially that in the outside box, that it's lower than the drain pipe (so that it maintains siphon).
4) Make the inside box height adjustable, so that I can adjust the water level in the DT.
I think we've covered all bases.
Devaji
5000 Club Member
the only HOB overflow I would personally trust is the lifereef ones. they start back up after power outage and dont need an aqualifer pump.
there hand made here in the US and he can custom make something if you need something special.
IDK just a thought.
yes I have use both. I know people use the other ones but that's just my 2 cents for what ever it worth. haha
all tho i do like the 2 drain design you posted above.
why not drill the tank?
there hand made here in the US and he can custom make something if you need something special.
IDK just a thought.
yes I have use both. I know people use the other ones but that's just my 2 cents for what ever it worth. haha
all tho i do like the 2 drain design you posted above.
why not drill the tank?
I can always remove it if it's not working. I thought it would be less maintenance with the pre filter sponge in the HOB box, than in the sump. You take it out of the box, rinse it, put it back in. Wouldn't take more than a couple of minutes. Also, there would be more space in the sump for filter media. Mind you my sump is quite small, only 16''L x 10''W x 10''H.
I'm in the UK, so it would be too expensive to import anything from the States I'm afraid. Furthermore, I've already bought the parts to build it.
Reasons I'd rather not drill the tank: a ) it's already running b) it's low iron glass and it would be much easier to sell it when I upgrade if it's not drilled.
Reefering1
Valuable Member
Yes, you have the option of removing prefilter. Keep in mind that as is gets dirty, water level rises and ato tops off(affecting salinity); to drop again when you clean it.
Imo, a drilled tank with permanent overflow will be worth more than a regular aquarium. But I personally would be hesitant of drilling because I'm scared of breaking the glass. I have a 75g just sitting here that I wish was already drilled, would have been set up already if it were... I know that kinda silly, but idk how to tell if its tempered glass(there is a sticker on bottom saying tempered.., does that include the side panes?)
Snoopy 67
Valuable Member
Option A only will work correctly.
Unless the baffle is not shown in B.
That baffle maintains water in the tube section keeping the tubes full on a shut down as long as the interior box has water in it.
Starts right up when water flows back into the tank.
Unless the baffle is not shown in B.
That baffle maintains water in the tube section keeping the tubes full on a shut down as long as the interior box has water in it.
Starts right up when water flows back into the tank.
That's another reason I'm not drilling it. I'm too clumsy, especially with glass.
The baffle is not necessary. The U-tube can remain in water as long as the drain pipe is tall enough and properly sealed. Check this out.
I'd like to keep it simple and don't rely on an Aqua Lifter.
I'll go with the second design and if needed I'll add a baffle.
Thank you all for your help!
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