sump design - level drop

[_shorty_]

How far can I drop water from level to level over a baffle without excess noise?

I'm designing a sump out of a 75, and wondering what the max level drop per baffle should be to keep noise down? I have about 1500gph flow through. I'd like to maximize water volume of stage 1 (as my water change reservoir), then drop about 10 inches from ther to where the return section will be. I was guessing I'd have to drop a couple times to reach the lowest level. Other techniques/tricks to do this in a quiet way?

 

[uncleof6]

Usally an inch is 'safe' noise wise, but it depends on the head height behind the baffle, and the flow rate, determined by the width of the sump. Using narrow sumps is asking for noise. For 1500gph you want to use a tank that is ~ 24" wide or more. Width will slow the speed (velocity) of the water at the same flow rate and lower the headheight, thus making it quieter (less water moving across the "weir" at any given point.) 18" is too narrow, but for some it may be satisfactory; a 10" drop is going to make you crazy, without a fairly wide channel (tank.) Stair stepping the drop is going to create a noisy stair case.

There are no tricks to get around fluid dynamics. You can't beat physics. However, if you can keep the water clinging to the baffle, you would probably be ok. (Why a thin sheet of water over the weir works) This would involve angling the baffle at a fairly 'shallow' or acute angle, somewhere between ; 0 and 45° 0 being parallel with the sump bottom and 90° being straight down. I have my doubts that a 75 gallon tank would be long enough to accomodate the baffle, (hypotenuse of a right triangle) depending on where the top of the baffle was vertically in the tank, along with everything else that NEEDS to be in a sump.

 

[_shorty_]

Usally an inch is 'safe' noise wise, but it depends on the head height behind the baffle, and the flow rate, determined by the width of the sump. Using narrow sumps is asking for noise. For 1500gph you want to use a tank that is ~ 24" wide or more. Width will slow the speed (velocity) of the water at the same flow rate and lower the headheight, thus making it quieter (less water moving across the "weir" at any given point.) 18" is too narrow, but for some it may be satisfactory; a 10" drop is going to make you crazy, without a fairly wide channel (tank.) Stair stepping the drop is going to create a noisy stair case.

There are no tricks to get around fluid dynamics. You can't beat physics. However, if you can keep the water clinging to the baffle, you would probably be ok. (Why a thin sheet of water over the weir works) This would involve angling the baffle at a fairly 'shallow' or acute angle, somewhere between ; 0 and 45° 0 being parallel with the sump bottom and 90° being straight down. I have my doubts that a 75 gallon tank would be long enough to accomodate the baffle, (hypotenuse of a right triangle) depending on where the top of the baffle was vertically in the tank, along with everything else that NEEDS to be in a sump.

thanks for the input... i guess I need to do some serious re-thinking on my design. So based on what you're saying, what if I ran a baffle length wise in the tank? - so ~48" wide baffle. What kind of drop do you think that would allow quietly? Not sure this will be feasable, though.

In addition, i didn't mention a 3rd chamber that I can potentially use to help with the step-down that I'll probaly 're-position', but I still deal with the same issue, just not as severely.

 

[mcgyvr]

WHY do you think you need to drop so far?.. There is NO reason for that..

 

[uncleof6]

thanks for the input... i guess I need to do some serious re-thinking on my design. So based on what you're saying, what if I ran a baffle length wise in the tank? - so ~48" wide baffle. What kind of drop do you think that would allow quietly? Not sure this will be feasable, though.

In addition, i didn't mention a 3rd chamber that I can potentially use to help with the step-down that I'll probaly 're-position', but I still deal with the same issue, just not as severely.

Perhaps this will help you visualize the problem. It is to scale, e.g. the total length is 48". How quiet it would be, is dependant on the head height above the "weir" (thick blue arrow) which is determined by flow rate, and width of the sump. This is a 45° spillway...Area 51 is dead space (unusable/empty.) To be honest and direct, the conceptual idea for a "reservoir" and long drop (stepped or otherwise) is not really worth the effort.

 

[_shorty_]

WHY do you think you need to drop so far?.. There is NO reason for that..

I was trying to maximize the volume in stage 1 for a water change area, and I like to have my return area fairly low to allow for plenty of room for water level to rise when everything is off. You are right, it's not absolutely necessary... So I'll be rethinking my design, but will be still be interested in maximizing the depth difference as much as reasonable.

 

[_shorty_]

Perhaps this will help you visualize the problem. It is to scale, e.g. the total length is 48". How quiet it would be, is dependant on the head height above the "weir" (thick blue arrow) which is determined by flow rate, and width of the sump. This is a 45° spillway...Area 51 is dead space (unusable/empty.) To be honest and direct, the conceptual idea for a "reservoir" and long drop (stepped or otherwise) is not really worth the effort.

Thank you for the diagram. Ill keep reviewing. I'll be rethinking my design with less depth difference.

 

[mcgyvr]

Not to mention a large pump + small return pump area = it will go dry/cavitate during startup for a bit.