Flow Rate Help Please

[Birdman]

This is for bottom drains. I know if you flow to little amount of water through the line from the bottom drain that seddiment will settle in the lines. Anyone know the correct flows for 3" and 4" lines?
Thanks,

[xiaohuang7]

Steve, I'm struggling with the same issue. I think 4" flow is 3800 gal/hr. But I don't know if that's max flow pressurized or gravity fed (guess gravity also depends on how much PE is behind it).

Gravity fed bottom drains are what I'm planning for, but I have the same fear as Steve, that the poop will settle and the water'll just flow over it. Someone answer Steve first, and then...

2 4" bottom intakes
1 4" mid-level intake (can adjust flow on this one)

Gravity fed to settlement tank, with 4500 gal/hr exiting the settlement tank.

Can someone answer without fluid dynamics equations?

Thx a lot. Much stomach churning over this.

[Birdman]

Quote: Originally Posted by xiaohuang7 Much stomach churning over this.

Yea, me too.

[bekko]

The velocity needs to be 20 centimeters per second to keep feces moving. A 4 inch pipe has a cross-sectional area of 80 square cm. At a velocity of 20 cm/sec, that's 1600 cubic centimeters per second = 1600 ml/sec
= 1.6 liters/sec
= 0.42 gallons/sec
= 1500 gallons per hour minimum flow to move feces.

3 inch pipe has cross-sectional area of about 45 cm2 x 20 cm/sec = 900 cm3/sec = 0.9 l/sec = 0.24 gal/sec = 864 gal/hr minimum flow to move feces.

A related and more frequent problem is bio-fouling inside the pipes. Snails, insect larvae mud tubes, and other things attach themselves to the inside of the pipe. This traps additional debris and the process snowballs. The process is somewhat self-correcting since the water velocity increases as the pipe becomes constricted. The higher velocity makes it harder for more material to accumulate. However, on a gravity fed drain, the pipe and flow can become constricted enough to lower the standing water level in the sump.

In designing the bottom drains, its nice to have some provision for reaming out the pipe if it becomes fouled. If there are no clean-out plugs, you can attach a string to a plastic golf ball and let the water flow carry the ball through the drian line and into the sump. Then attach a large abrasive scrubby thing (technically called a 'pig') to the string and pull it back and forth through the pipe to clean it.

-hopkins

[mekoi]

Hi Hopkins,

What about flashing the pipe by emtying the sttlement and opening the BD slide valve. I've done this last weekend and I've noticed all the crap that came out in the settlement. I know for sure that those craps didn't come out of the pond coz the bottom are just full of carpet algae. If I do regularly say once a month, will this prevent the muck build up???

rgds,
Jon

[Birdman]

Thank you very much Hopkins. That is exacrly the info I was looking for. I will go with 4" lines as I hope to be flowing 3 to 3,500 GPH. It will be very eacy for me to put in a cleanout where the line splits in two to go to the two Vortex Filters.

[Birdman]

Quote: Originally Posted by mekoi Hi Hopkins, What about flashing the pipe by emtying the sttlement and opening the BD slide valve. I've done this last weekend and I've noticed all the crap that came out in the settlement. I know for sure that those craps didn't come out of the pond coz the bottom are just full of carpet algae. If I do regularly say once a month, will this prevent the muck build up??? rgds, Jon

I also do this Jon with my existing system. The 1st few times I got a lot of bad water but now it's pretty much clean all the time.

[xiaohuang7]

thanks a lot for your expertise hopkins. that tidbit (and most other things on this board) help tremendously.

- john

[mekoi]

Quote: Originally Posted by Birdman I also do this Jon with my existing system. The 1st few times I got a lot of bad water but now it's pretty much clean all the time.

Hi Birdman,

Thats what I've noticed too coz I just did the flashing today and didn't much crap.

I might do this on weekly basis until I hardly see any crap

rgds,
Jon