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Old 02/14/2019, 03:37 AM   #1
ocram
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Herbie emergency drain hight

Hi guys

I'm planning a Herbie style overflow with a trickle down the emergency drain. I noticed that everyone seems to choose the emergency drain hight lower than the weir, so that the water drops down by about 1/2 to 1 inch.

What would be the cons of mounting the emergency drain a little higher, so that the water does not fall down in the overflow box but instead "just flows in".

As a pro, I see no noise at all.
A con could be less room to the top of the tank and therefore less room for the edrain to start a full syphon. That however wouldnt bea concern in my tank.

Thanks, Marco


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Old 02/14/2019, 03:09 PM   #2
d0ughb0y
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you will get noise on the drop if your flow is really high. so high that water shoots forward and drops instead of the intended design of water coming down attached to the inner wall of the box.


if you make the emergency higher, level might bounce, as water will try to exit the emergency first, then main gets less water, so level goes down, then fills up again to emergency and cycle repeats.


is your overflow box two layers?


on mine, there is an inner box and an out box about 1/4" or so apart. The outer box has slots near the bottom where water can get sucked in. The flow is induced by Bernoulli effect at the top hence the drop is necessary to create the fast water flow speed between the inner and outer box gap to create the sucking action so water flows in from the bottom slots. I think this is a genius design.


if your emergency is slightly lower, it will muffle the trickle sound more.



I made mine 2 or 3" lower, can't remember for sure, but definitely not 1" or less.


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Old 02/19/2019, 03:22 PM   #3
ocram
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Hi, thank you very much for your reply.

However, I'm not sure if I understand. Why might the water level bounce if the emergency drain is a little higher so that the water does not drop but just flow in?

I do not have an inner and outer box, I'm planning an external overflow box with no inner box but just a weir in the back wall. Should be the same principle as having a traditional in tank overflow section

Would really appreciate an explanation

Thanks Marco


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Old 03/16/2019, 06:14 AM   #4
reefteaser
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Read this, it helped me very much. Other plumbing info on this site was very interesting as well.

http://gmacreef.com/herbie-overflow-...method-basics/


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Old 03/26/2019, 08:47 PM   #5
wildman926
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Your emergency drain needs to be 1/4" higher than your main drain. It will be super quiet.


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Old 03/27/2019, 10:08 AM   #6
Vinny Kreyling
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Wildman926, if you read the link above it recommends about a 6" difference.
On mine there is too much variation in height levels to to consider much less.
I believe there would be a lot of water in that emergency drain with such a tight difference.


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Old 04/12/2019, 10:45 AM   #7
Nrdau
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Mine is about a 1/4 inch above main drain and I haven’t had any problems in five years


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Old 04/13/2019, 08:41 AM   #8
Salty Waffles
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When I set up my dual Herbies, I set my emergency drains about 3" below the weir. The mains are about another 2" below those.

I don't get any noise from the overflows unless I turn the pump up to flow more than the weirs are designed to handle.

Right or wrong, my reasoning for going so much lower on the main drains was to avoid the mains sucking air from a whirlpool effect from being so close to the water surface. It seems to me that if your main drain is only 1/4" below the emergency this would be a real concern. But I'm just speculating here....


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Old 04/14/2019, 07:41 PM   #9
wildman926
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Quote:
Originally Posted by Vinny Kreyling View Post
Wildman926, if you read the link above it recommends about a 6" difference.
On mine there is too much variation in height levels to to consider much less.
I believe there would be a lot of water in that emergency drain with such a tight difference.
I don't need an article to tell me how to run a Herbie drain, when I have been running them for over 10 years on 2 different tanks.


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