Maximum gravity fed throughput on pipe sizes

[george]

Anyone have any information on maximum gravity-fed throughput by pipe (or preferably bulkhead) diameter?

I found info on absolute pressurized maximums and the ReefCentral head loss calculator helps, but I'm looking for no pump rates like you'd get through overflow pipes, but not the overflow maximums which I also found.

 

[dannybradley]

That's a loaded question. The variables that come into account are distance and diameter. Are you just looking for the max flow you can get from a system pump?

 

[stanfill reef]

As a rule of thumb I try to design systems (industrial wastewater) at 2 feet per second (fps). At less than that you are likely to get solids deposition in the piping. If you go above about 4 fps you will start getting problems due to friction and air entrainment. Try to keep your gravity piping as straight as possible and don't allow it to have a high spot in the middle or you can get an air lock or reduced capacity.

Using 2 fps I get:
Diameter (in)----> Flow (gph)
0.25--------->18
0.5---------> 73
0.75---------> 165
1.0---------> 294
1.5---------> 661
2.0---------> 1175
2.5---------> 1836
3.0---------> 2644

Your maximum flow rate in the pipe will be higher, but these flows are safe. I have attached a spreadsheet that you can play with if you want to explore more flows.
<fieldset class="gc-fieldset">
<legend> Attached files </legend>

 

[ouling]

I tested a 1.0'' PVC with a 2'' flange opening and a spray bar at the end pulling down 750GPH in 4ft. Alot of flushing noise but it's pulling it down, and i'm not talking about the U-tube, it's just a 1'' drilled with a 2'' mouth.

If you can stand the noise, a 1'' RR drain can take a Mag9.5 at 5ft head.

 

[frewl]

How far from the top of the water line will it be? I'm looking at the chart that is in <u>The Reef Aquarium vol. 3</u>. It varies depending on depth and diameter.

 

[george]

DannyBradley;58807 wrote: That's a loaded question. The variables that come into account are distance and diameter. Are you just looking for the max flow you can get from a system pump?

Not with a pump. I'm looking at how much water I can count on (roughly) draining through a 1" bulkhead and a 3/4" bulkhead at the bottom of an overflow. The exact situation is that a pre-drilled tank has an overflow with a 1" exit and what is supposed to be a 3/4" return, but I want to use the return hole to drain as well and want to figure out the capacity of the two together.

Flow is probably limited more by the overflow's capacity than the bulkhead's capacity in this case.

Frewl;58885 wrote: How far from the top of the water line will it be? I'm looking at the chart that is in <u>The Reef Aquarium vol. 3</u>. It varies depending on depth and diameter.

Well, I guess I should get to reading. I just bought that book this week. Didn't know there was a chart in it. Thanks!

 

[stanfill reef]

My numbers assume that you are free flowing into the pipe, i.e. a surface overflow. If you surcharge the pipe (have the pipe entrance completely submerged with additional water above it) you can get more flow. The maximum that you can put through the pipe depends on how much pressure the water is exerting. If you do let the water surcharge above the overflows, make sure that you have enough room in your sump for the tank to drain to below the overflows when the power goes out. A 1/2" of water in the tank can be a lot in a smaller sump.

 

[george]

Thanks for the info all. The main reason for this wasn't for continuous flow, but for handling surges caused by things like a Carlson Surge Device.

 

[dannybradley]

What if you kept your over flow pipes about 2" high? This would allow your overfow box to help contain the extra water suddenly hitting the tank, allowing that the box will fill up fast enough to prevent the tank from overflowing.

Running a lower system water flow should allow for a really low level in your over flows, and since you're using a surge for water movement, you can probably compromise a little system flow for auxiliary flow. Water moving slower through a sump gets filtered better anyway, as it spends more time in contact with media.

 

[frewl]

The chart I'm talking about is on page 93. it gives the flow in gallons per minute but that is easily converted. I hope that helps.