Question on the Herbie-style Overflow - Basic Principle & Question

[dfleary]

The advantage of the Herbie-style overflow is that it is silent. Is it true that this is only because the overflow rate can be closely matched to the rate of the return (using a gate valve between the overflow and the sump)?

If that is true, then why couldn't you install the gate valve between the return pump (particularly a Diablo DC variable-speed pump) and the water return in the tank to get this same "equalizing" effect?

Is my logic flawed? I'm no engineer - just trying to plan my future plumbing design, and I want it as quiet as I can get it with the Marineland Corner-flo pre-drilled tank that I already have. -- It would be nice if that worked, and there would be no need for an emergency overflow. This would eliminate the need to drill a return into the side of tank or run the return line behind the tank and over the side!

[jimmyj7090]

It's quiet because there is no air in the drain line. The inlet and output from the drain are both submerged so there is no splashing or sucking noises.

All overflow designs match the drain and return rate because drains need to handle the return rate or the tanks would flood.

You could potentially control a herbie by using an oversized pump and throttling it back to match the max flow rate down the siphon drain, but it's easier to restrict the drain to get the same result.

Any drain that relies on a drain and return running the exact same rate will need a back up drain because those rates will always be prone to some fluxuation (pump gets slightly fouled, something tiny gets stuck in the drain, atmospheric pressure varies, exct....)

[5pacey]

Originally Posted by dfleary

The advantage of the Herbie-style overflow is that it is silent. Is it true that this is only because the overflow rate can be closely matched to the rate of the return (using a gate valve between the overflow and the sump)?

If that is true, then why couldn't you install the gate valve between the return pump (particularly a Diablo DC variable-speed pump) and the water return in the tank to get this same "equalizing" effect?

Is my logic flawed? I'm no engineer - just trying to plan my future plumbing design, and I want it as quiet as I can get it with the Marineland Corner-flo pre-drilled tank that I already have. -- It would be nice if that worked, and there would be no need for an emergency overflow. This would eliminate the need to drill a return into the side of tank or run the return line behind the tank and over the side!

Yea... no way around that unfortunately unless you are willing to compromise safety and use the 2nd hole as a return. But that is highly non advisable.

Spacey

[mussel and hate]

The whole point of the Herbie style overflow is to run the primary drain as a siphon tuned by a gate valve with the secondary as a back-up overflow.

[barjam]

Actually the rate has to exceed the drain rate at zero pressure. As the pressure rises the full siphon reaches an equilibrium. No air gets into the drain so no noise.

[dfleary]

Originally Posted by barjam

Actually the rate has to exceed the drain rate at zero pressure. As the pressure rises the full siphon reaches an equilibrium. No air gets into the drain so no noise.

. . . The return rate has to exceed the drain rate? And what does the zero pressure refer to?

[jimmyj7090]

In other words the valve restricts the drain so it backs up (return exceds drain), as it backs up the pressure increases/siphon starts. As it siphons, with the valve adjusted correctly, it will balance out so that the drain is backed up a little bit (so the intake is submerged and no air is drawn in) but not backed up enough to reach the back up drain.

[dfleary]

Originally Posted by jimmyj7090

In other words the valve restricts the drain so it backs up (return exceds drain), as it backs up the pressure increases/siphon starts. As it siphons, with the valve adjusted correctly, it will balance out so that the drain is backed up a little bit (so the intake is submerged and no air is drawn in) but not backed up enough to reach the back up drain.

That is the best explanation for it I have heard yet. Understandable - thanks!

Now, is there any reason why the main return should just be a plain old stand pipe? For instance, if I have the two 90-degree elbows that came with my tank (for a durso-style overflow), could I put them on top of the stand pipe too?

[SGT_York]

A durso stand pipe would add no additional benefits to a siphon. Durso's are meant to keep air flowing down the pipe to prevent a temporary siphon (loud gurgling sound) All you want on a herbie is a snail guard.

So yes you could, but there would be no point in it and it may possibly create problems.

[jimmyj7090]

But you could use two 90s to make the inlet to the siphon point down. Mine seems to run a little smoother that way though I can't explain why.

[dfleary]

Interresting. Good to know I can try it out! Thanks!

[leveldrummer]

if you use 2 elbows so the siphon points down, then you have to be careful how deep the bottom of the drain pipe is submerged in your sump. i had issues getting my syphon to start when my drain line was too deep in my sump, the water pressure wasnt enough to force the air out and it would chug and make noise but never really start a proper siphon, so consider that as you set your system up.

[jimmyj7090]

Also be careful of angled drain line, they can wreak havoc on siphon drains.

[dfleary]

Angled drain lines directly beneath the standpipe?

[jimmyj7090]

"Angles" more like going a couple or more feet across. Like going the length of a tank to reach a sump under another tank.