Well actually a Herbie can drain more flow without using the back-up, provided it's done properly. For example if you have a standard Durso and you cover the air hole on the top you'll start a siphon and you'll be able to take more flow, this is especially a Herbie but you fine tune the flow rate with a gate valve to match the return and run a back up drain encase of the perfectly matched flow becomes unmatched. It's not a mystery but rather the effect of head pressure, so ideally the drains are placed at the bottom of the overflow and no extension tubes are used, this will however result in the entire overflow box draining during a power outage.

You can get around the overflow draining issue and you can also use a standard standpipe instead of a straight tube for back up. This will allow you to put a little flow through the back-up resulting a less finicky system and almost as quiet.

This is a system I commonly employed when I did installs, however it's better to have the two drains enter the sump separately rather than joining together first as shown.

http://i84.photobucket.com/albums/k3.../trimetric.jpg

http://i84.photobucket.com/albums/k3...frontnoted.jpg

It kind of can, but not really. A 1" pipe takes 600 gph no matter which way you try to shove water down it. It's just that which a Herbie you don't have a bunch of air taking up room in the pipe.

My thoughts behind the question:

Traditional overflows have air introduced into them to quiet them down. The overflow works on a weir type principle ( might be the wrong term ) Water flows over the edge of the pipe (HGB) and up through the pipe ( Duroso ) Since air is introduced into the system you have air mixed with water traveling down the pipe. With a herbie no air is introduced into the pipe, therefore space previously occupied by air is now being taken up by water. On top of that you are also introducing head pressure, how much of a difference that makes is up in the air.

Is this like being a little bit pregnant?

Opps I was too late with my thoughts...

A Herbie standpipe potentially could flow more in that it's a siphon but then to create the Herbie you're restricting the flow with a valve to have the water back up over the top of the stand pipe.

Would think for estimating probably not to far off with the commonly used gravity flow rates (~600gph for the 1").

Well we can dispute this forever but if you measure the pressure in the drain line (near the base) a Herbie will show a higher pressure than a Durso as no air will be in the line. A Durso may typically show close to atmospheric pressure while a Herbie will show a pressure equal to the height of the water above it. More pressure means a higher velocity and therefore more flow. How much more? Hard to say as it will totally depend on the setup. You can also eliminate most of the air from a Durso style drain if done correctly. Some people will see more dramatic results from a change over because their Durso style drain was never done correctly, while others don't notice anything.

The bottom line here however is that the main purpose of a Herbie style overflow is not more flow but rather noise and air bubble reduction. If you want more flow you should increase the pipe size or add a second drain, it really is as simple as that.

Hey I'm not arguing but seen on RC someone was figuring he could get 1000gph from a 1" drain, seemed a bit much.

Exactly.

And if you make the overflow the correct size there will be no noise and no need for a Durso.