Chizer & Bunoi 67 gallon

[sphelps]

First off don't lower the full siphon pipe yet (primary, one with gate valve). This won't increase head pressure or flow, this is set by the gate valve and nothing else. Lowering the height will only drain more water to your sump and that's a pretty big overflow you got there. You may need to lower it if it's creating a vortex and sucking in air but I don't think that's an issue.

Seems to me the issue is your back up or emergency drain is too low. Try this procedure.

1. Stick a coupling on there or swap out the pipe with a taller one. Start with something too tall that extends an inch or so above the top of the tank, you can cut it to the right size after the next step.
   
2. Tighten the gate valve a little to raise the water level in the overflow, it's too low if the weir is dropping down too much causing waterfall noise. Water level in the overflow can be around 1/2" to 1/4" below tank water level, but set it as low as possible provided the noise is gone. The overflow should be completely silent now, if not check if the primary is creating a vortex and sucking in air, if it is the primary pipe needs to be shortened.
   
3. Now with the overflow water level set, mark the back up drain pipe 1/2" above the overflow water level and cut it there. I recall you have three drain pipes, so consider running two back ups at this height, it'll help for next step.
   
4. Now test the back up, with pump operating at desired or max output shut the gate valve completely but be ready to open it if needed. If the back up drain(s) can handle the flow without the tank overflowing you're good. If not you have to shorten them until they can, 1/4" at a time but note if you have to cut it more than once you'll need to lower your overflow water level in step 2.

[lastlight]

I've had my emergency that close to my primary. They key is making really fine adjustments to the gate valve so that the trickle going down the emergency is small enough that it is silent... like a thin coating of water on the walls of the pipe going down.

Greg - I edit that part out. I realized I wasn't using an aquarium calculator. duh!

Skimmin - Thanks for the kind comments. I was able to leave the return pump fully open.

Steve - Your method worked very well. It sure is time consuming and cutting a 1/4" of PVC off on the mitre off is scarry. The rebound and kick back sure is dangerous.

Brett - I have my emergency drain sitting high in the sump so the thin drain doesn't work. I did this on purpose so that I could whether something was wrong with the primary.
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Thank you everyone. I ended up cutting the primary 1" and the emergency is now sitting 1/4" under the weir itself. No crashing noises or vortex happening. The emergency also works flawlessly.

I stuck a piece of 1" gym memory foam under the return pump which helped some what dampen the noise, but you can still hear a hum/vibration. I'm thinking maybe it's the vinyl tubing from the pump to the hard pvc? Or maybe I am hearing the echoing inside the stand itself?

There are only two drains on this herbie.

[sphelps]

Originally Posted by ChizerBunoi

Steve - Your method worked very well. It sure is time consuming and cutting a 1/4" of PVC off on the mitre off is scarry. The rebound and kick back sure is dangerous.

Ha, I know all about that. Keep the saw down until the blade stops moving. You usually get a kick back by lifting it back up with the blade still going full tilt.

Glad you got everything working.

[midgetwaiter]

Originally Posted by sphelps

First off don't lower the full siphon pipe yet (primary, one with gate valve). This won't increase head pressure or flow, this is set by the gate valve and nothing else. Lowering the height will only drain more water to your sump and that's a pretty big overflow you got there. You may need to lower it if it's creating a vortex and sucking in air but I don't think that's an issue.

Actually lowering or removing the primary drain standpipe will make life a lot easier in this configuration and it has everything to do with "head". Everybody remembers their first go at trying to adjust a herbie style overflow, even if you did shell out the bucks for a gate valve it can be a complete PITA to try and maintain with the primary standpipe that high.

However if you were to remove the primary drain standpipe and close the valve controlling that drain until the water level in the overflow stays within and inch or so of the top it so it's quiet as well it becomes much easier to do minute adjustments. The reason for this is the pressure built up in the box remains constant when it is at at given level, with a high drain pipe you get much less drain pressure and it fluctuates somewhat making it difficult to adjust. The force of the water is "static head", not to be confused the the "head pressure" we try and work out when sizing a return pump.

Some things to consider in this configuration; When the pump shuts down you will drain the entire overflow box, make sure you have room to catch the water. Also you are at a slightly increased risk of clogging the drain, make sure you open it up once in a while to flush built up gunk. You should be doing that in either configuration though.

Originally Posted by midgetwaiter

Some things to consider in this configuration; When the pump shuts down you will drain the entire overflow box, make sure you have room to catch the water. Also you are at a slightly increased risk of clogging the drain, make sure you open it up once in a while to flush built up gunk. You should be doing that in either configuration though.

Thanks for the tip. I didn't glue the stand pipes in for maintenance purposes. Also when I open the gate valve completely, it does a nice job of flushing the sump so that should be a regular task.

I chose not to use the ball valves to limit the return pump. Kinda silly since I them on there already huh? I think I'll stick with the stand pipe.

[sphelps]

Originally Posted by midgetwaiter

Actually lowering or removing the primary drain standpipe will make life a lot easier in this configuration and it has everything to do with "head". Everybody remembers their first go at trying to adjust a herbie style overflow, even if you did shell out the bucks for a gate valve it can be a complete PITA to try and maintain with the primary standpipe that high.

However if you were to remove the primary drain standpipe and close the valve controlling that drain until the water level in the overflow stays within and inch or so of the top it so it's quiet as well it becomes much easier to do minute adjustments. The reason for this is the pressure built up in the box remains constant when it is at at given level, with a high drain pipe you get much less drain pressure and it fluctuates somewhat making it difficult to adjust. The force of the water is "static head", not to be confused the the "head pressure" we try and work out when sizing a return pump.

Some things to consider in this configuration; When the pump shuts down you will drain the entire overflow box, make sure you have room to catch the water. Also you are at a slightly increased risk of clogging the drain, make sure you open it up once in a while to flush built up gunk. You should be doing that in either configuration though.

Completely false in regards to how pressure works, basic fluid mechanics here guys it's very simple.

Look at these two cases, the static head pressure at the valve (X) is identical for both cases. It's science don't argue with it cause you'll loose

Shortening the pipe will do nothing for pressure and unless you're getting a vertex it will make no difference for adjustment and only result in issues relating to the entire overflow box draining during shut down.

[kien]

Originally Posted by sphelps

Completely false in regards to how pressure works

so what you're trying to say is that size doesn't matter??

[midgetwaiter]

Originally Posted by sphelps

Completely false in regards to how pressure works, basic fluid mechanics here guys it's very simple.

Look at these two cases, the static head pressure at the valve (X) is identical for both cases. It's science don't argue with it cause you'll loose

You assume that the volume of water coming over the weir is constant but it's not. Having a larger volume of water over the drain makes adjustment easier because it evens it out.