Herbie Drain
 

I have a 110G tank that has a corner overflow with two holes drilled in the bottom of the tank. The Tank came with one 1 1/2" an a 1" pvc pipes. One hole will be my main drain an the other will my emergency drain. I have another hole drill in the back of the tank for my return. Does it matter which one of the two different size pvc pipes I use for my main drain ? Should they both be 1" diameter ? I also have the gate valves needed for the setup.

Use that bigger of the 2 for your main drain, less chance of something plugging it off.

Is one hole 1" and the other is 1-1/2" or are they the same?

If they are different us the bigger of the 2 for the emergency and put the gate on the smaller of the 2. If they are the same keep the pipe size the same if you can.


Oh, and welcome to Canreef!!

The holes in the bottom of the tank are both for a standard 1" bulkhead fitting. The two pipes above are what are different sizes. The smaller of the two pipes I assume was supposed to be used for the return.

If the BH's are the same it won't matter which you use for a drain, or what size you use above or below. If 1" is the most narrow point that is how much water you can handle through it.

http://flexpvc.com/WaterFlowBasedOnPipeSize.shtml

Thanks guys, parkinsn do I put the gate valve on both drains or just the main ?

just the main, you dont want any restrictions on the emergency.


also you should have your emergency slightly out of water so it only sees water during a emergency.

For the emergency drain using a larger pipe of 1.5" above a 1" bulkhead is actually ideal if possible. A 1.5" riser will flow more water than a 1" riser despite the bulkhead being 1" for both cases. Same rules apply to standpipes, usually for best results your standpipe should be one or two sizes larger than the bulkhead. This just allows higher flow at the entry point which has zero head pressure as appose to the bulkhead which can potentially have head pressure equal to that of the standpipe height.

Awesome, thanks.

With a herbie, you always want your emergency drain to be equal to or greater then your primary. If the primary is larger and backs up the emergency drain will not be able to handle the same amount of flow. You don't need to valve the emergency, it's only there as a just in case.

Technically thats not true Robb......the primary should be able to handle the entire flow that the return puts into the tank, with the gate valve open all the way.....so if the emergency is the same diameter, then it should also be able to handle the flow if the primary drain is restricted more than the gate valve being closed to adjust the water line in the overflow......did that make sense? :noidea:

depends on the setup, an internal overflow for example could have two drains of equal size but the owner may decide to run the primary without a riser or a very short one which in a way is like a full siphon with the full height of the overflow adding to it's pressure. The back up will have a riser to the height of the overflow and won't be able to replicate the same pressure as the primary and fall short of matching the flow. However if the water can rise high enough over the emergency riser the effect will be very similar minus the friction and minor losses from created from the riser and it's entrance point but the amount you can allow the water to rise over the riser tube depends on how much clearance you have. The larger diameter to riser tube the closer you'll come to matching the capabilities of the primary.

On my set-up I don't run a riser on my primary and my emergency has a riser pretty close to 30" tall.

With the two pipes how far below the slots on the corner overflow does the main drain need to be ? An should the emergency drain be a 1/4", 1/2" , 3/4" , or 1" above the main drains height ? Can take pictures of my corner overflow if that helps too.

http://i797.photobucket.com/albums/y...2/IMG_0031.jpg
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http://i797.photobucket.com/albums/y...2/IMG_0030.jpg