Flow rate chart for overflow bulkhead sizes?

[mmelnick]

I have found a few charts like this one:

http://www.wetwebmedia.com/BulkheadFloRateArt.htm

 

But none of them have a calculation to show how much the heigth of the hole will effect flow. The one I used when I set up my current tank calculated how much the flow would change when you moved the hole up or down because the weight of the water above the hole will increase flow through the opening. Does anyone know of a chart or calculator like this?

 

Thanks.

[mmelnick]

Bump

[Stephen-in-Va]

I have this PVC flow chart. It's not specific to bulkheads but from what I've tested it's pretty accurate with gravity flow through PVC. Of course over distance and turns friction loss will reduce the flow some.

[mmelnick]

Thanks. I guess that might be the best I'll find. I know there was one that would calculate how much the flow would increase with water over the hole. But I can't find it. I suppose it could have disappeared over the last couple years.

[jeremai]

I'm confused - the only reason this information would be relevant is if you have the water draining through the bulkhead without any sort of surface skimming overflow enclosing it. right?

[mmelnick]

I'm confused - the only reason this information would be relevant is if you have the water draining through the bulkhead without any sort of surface skimming overflow enclosing it. right?

 

 

No.

 

Take my 20H for example...

 

I have a 1 1/4" hole in my bulkhead. It is installed in a hole drilled in the glass that is towards the bottom of the tank inside an overflow stand that I made out of a piece of 4" ABS (cut in half length ways and siliconed to the back wall). It can flow a certain amount of water. However, if the water ever starts to back up because there is too much flow the water level can rise up to 12" inside the overflow stand and the pressure of that water will push down on the water below and allow for a higher rate of flow. I still have surface skimming but this takes place as the water flows over into the overflow stand from the main display.

 

Think of it like this... If you have a water container that is 10 feet tall and 4" wide and it is full of water and you poke a hole in the bottom it will flow really fast. The weight of the water above will push the water below out.

 

Now take a 2" tall container that is still the same 4" width and make the same size hole and you will have a much lower rate of flow out of that hole because there is no pressure from above.

 

 

 

What I am looking for is a chart or online calculator to tell me how much flow I can count on if I ever get to the point where water starts to back up the overflow pipe.

[jeremai]

given the overflow rate of the surface skimmer is higher than that of the bulkhead, the bulkhead will flow water at the gravitational rate offered on the chart above. I understand what you are trying to say, but in my experience the difference in bulkhead flow rate at the surface of the water or a foot under it isn't appreciable. the water backing up in the overflow chamber won't magically push water into the sump, it will just continue to back up the chamber until it, well, overflows. if the level in the overflow chamber isn't reaching an equilibrium, you need a smaller return pump. if you hear hoofbeats, think horses and not zebras. err on the side of caution and go by the basic gravitational flow measurement.

[mmelnick]

the difference in bulkhead flow rate at the surface of the water or a foot under it isn't appreciable. the water backing up in the overflow chamber won't magically push water into the sump, it will just continue to back up the chamber until it, well, overflows.

 

It's simple physics. And yes the height difference from a foot to the surface will make a pretty good difference. I'm just trying to remember how much.

 

My current bulkhead was rated for 450 GPH, but since I have room above the fitting in the overflow stand I have ran 800 GPH and it would run with the water level 1/2 way up the stand.

 

I was running a smaller pump in my sump and it would drain right away. There was no water building up the drain stand.

 

When I switched to the 800GPH sump pump (640GPH after the lift from the sump) the water level would rise but not overflow. Once the increased flow had raised the water level the higher water level was able to increase the drain rate. It absolutely works that way. It is simply a matter of physics. And that's why you should always put the bulkhead as close to the bottom as possible. I was running more than the 450GPH rated flow, but due to the water level building up it was able to find a level of equilibrium and drain a higher GPH without raising the water level any more.

[bitts]

this is my fav

http://www.grow.arizona.edu/Grow--GrowReso...?ResourceId=188

 

hope it helps.

[mmelnick]

this is my fav

http://www.grow.arizona.edu/Grow--GrowReso...?ResourceId=188

 

hope it helps.

 

Yeah, thanks!

 

 

That was the exact one I was looking for

 

 

 

in my experience the difference in bulkhead flow rate at the surface of the water or a foot under it isn't appreciable.

 

Hopefully this link can explain it better than I can. But a 1" hole at a 1" depth will flow 5.64 GPM 338 GPH.

 

Now take that same 1" hole and move it to the bottom of the overflow stand... say 12"... you now get19.55GPM, which is 1,173 GPH.

 

 

So yes, it does make an appreciable difference. The same 1" bulkhead that is rated for a little more than 300 GPH can actually flow well over 1,100 GPH if you set up your overflow system correctly.

[jeremai]

lol, the physics I understand, I'm not a noob here. yeah, I'd rather plan for the worst than hope for the best, especially where plumbing is concerned - in my experience, if you want more flow, get a bigger bulkhead, don't try and super fine tune the water level in your overflow chamber. horses and zebras. but hey, more power to you.

[mmelnick]

in my experience, if you want more flow, get a bigger bulkhead, don't try and super fine tune the water level in your overflow chamber.

 

Of corse. I was just trying to find the charts to help with selecting the right bulkhead for my new tank and wanted the good one.

 

Thanks again bitts!

[bitts]

jeremia think of it like this. if your filling a cup at the water cooler, the cup fills faster when the jug is new. as it drains it takes longer and longer to fill the cup. given the hieght of the water above the opening combined with the openings size, you can determin the flow thourgh said opening. you just need the right equation. if the opening size changes then the flow rate will change. thus the need for a backup drain when running a herbie style drain system.

 

mmelnick, no problem. happy to help if you have any other questions, ask. will help if i can.

[jeremai]

[disaster999]

given the overflow rate of the surface skimmer is higher than that of the bulkhead, the bulkhead will flow water at the gravitational rate offered on the chart above. I understand what you are trying to say, but in my experience the difference in bulkhead flow rate at the surface of the water or a foot under it isn't appreciable. the water backing up in the overflow chamber won't magically push water into the sump, it will just continue to back up the chamber until it, well, overflows. if the level in the overflow chamber isn't reaching an equilibrium, you need a smaller return pump. if you hear hoofbeats, think horses and not zebras. err on the side of caution and go by the basic gravitational flow measurement.

 

you probably should get more experience then before you say that again

[disaster999]

lol, the physics I understand, I'm not a noob here. yeah, I'd rather plan for the worst than hope for the best, especially where plumbing is concerned - in my experience, if you want more flow, get a bigger bulkhead, don't try and super fine tune the water level in your overflow chamber. horses and zebras. but hey, more power to you.

 

thats just a waste of money and end up in a bigger headache. no #### a bigger hole will flow more water, but that results in overly large plumbing than it needs to be...which requires more space because of turns and Ts and elbows etc, which is more weight, and cost more.

 

"super fine tuning" the water level in the overflow chamber isnt hard, its called a herbie style drain

[jeremai]

wow, someone didn't eat their cheerios today.

[disaster999]

hmm, i can think of anything smart to say, i guess ill use the cheerios, that will get them every time...