Settlement tank

[Todd Inniss]

I have approximately 4500 gallon pond with two systems I am installing. One is skimmer box with 8000gph pump going to large waterfall filter. I just added a gravity feed 4" bottom drain to a settlement tank 275 gal square size feeding a 55 gallon drum bio filter. I am trying to size the pump for the bio filter return. I am trying to balance pull on the bottom drain and "settle" time in the chamber. I am also considering reducing the inlet in the settlement tank from 4" to 2" to create some velocity and hopefully a bigger pull but I am concerned about resistance. Any and all comments, suggests would be helpful. thanks

 

[Meyer Jordan]

Doing a pipe size reduction on a gravity feed system is asking for trouble.

 

[Todd Inniss]

I meant reduce the outlet in the settlement tank to 2" but keep inlet and pipe to settlement tank 4'

 

[Meyer Jordan]

A 2" line does not allow for a very large flow rate. You would have to use a considerable smaller pump than the 8000 gph waterfall pump.
On a different, but connected, note. What size is your waterfall? That seems like an awfully large pump for feeding a waterfall for a 4500 gallon pond unless you are looking for a lot of 'splash for your cash'.

 

[Faebinder]

A 2" line does not allow for a very large flow rate. You would have to use a considerable smaller pump than the 8000 gph waterfall pump.
On a different, but connected, note. What size is your waterfall? That seems like an awfully large pump for feeding a waterfall for a 4500 gallon pond unless you are looking for a lot of 'splash for your cash'.

Maybe it can feed multiple waterfalls or a filter plus waterfall?

 

[budgenator]

Well let's see a

• 4 inch BD (Bottom Drain) pipe needs about 2500 gph to keep the pipe swept clear,
• The general rule for SC (Settlement Chambers) is 10% settling volume verses flowin GPH, so 2500 GPH would need at least 250 gallons.
• The other General rule for SC is 3 minute dwell time, 2500 GPM is ~42 GPM, 42*3 is 126 gallons

So your settlement chamber is about the right size.
55 gallon drum as a static filter the flow rate should be below 2000 gph & closer to 1800 gph max, so you might be better off with two.

 

[Todd Inniss]

Im sorry let me give more detail. I started with the pond with just a skimmer box connected to a waterfall bio filter. there is a 2 inch line from the skimmer box underground to the waterfall filter which is 3 feet above grade. There is a 8000 gph pump in the skimmer. I went higher on the pump size to make sure i got good flow for the waterfall which is 3 feet above grade. the weir on the waterfall is 21 inch. the waterfall bio box is a 3 stage filter that is probably about 30 gallons. It is supposed to accommodate up to 5000 gallon pond. I then decided to put in a bottom drain. It is 4 inch bottom drain with an air diffuser on top. The 4 inch pvc connects about 1/3 from the bottom of a 255 gallon tank next to pond that is in the ground. the settlement tank is connected to a 55 gallon barrel filter with a 3inch pipe feed from or near the top of the settlement tank to the near top of the barrel bio filter. Im using ribbon in the bio barrel filter around a 4 inch vertical pipe in the middle, I am drawing water from inside the 4 vertical pipe but from the bottom underneath the ribbon. the ribbon is elevated about 3 inches from the bottom and I am drawing the water from underneath the ribbon. of course the idea is that as the bio barrel filter draws water out of the settlement container gravity will pull water from the bottom drain. I have not purchased the pump that will draw the water from barrel filter and return to the pond, thus creating the vacuum letting gravity feed the settlement container from the bottom drain. I am thinking a 1600 gph pump to maximize settlement time but still turn over water. the return would be about 1 foot below water level and hopefully aid in pushing debris towards the bottom drain. my thought was to decrease pipe size inside the settlement tank at the outlet to 2'. the increase in velocity should increase the draw from the bottom drain. ( I think) but am i creating resistance thereby decreasing flow? is the 1600 gph pump for the bio barrel sufficient or should I go bigger or smaller. remember that the skimmer water fall is also filtering water? thanks for the help

 

[Meyer Jordan]

With both filters (waterfall and gravity fed) you should have ample biofiltration. The point is operational efficiency. There must be enough flow at the BD to insure proper functioning. A minimum flow rate of 2500-3000 gph for a 4" BD is widely accepted. Anything less may result in particle collection in the plumbing.

 

[budgenator]

( I think) but am i creating resistance thereby decreasing flow? is the 1600 gph pump for the bio barrel sufficient or should I go bigger or smaller. remember that the skimmer water fall is also filtering water? thanks for the help

The hazard with using a 1600gpm pump is the 4 inch from the bottom drain needs about 2500 gpm to keep the sediment from clogging the pipe. The 2500 gpm flow through the sediment chamber is within the numbers that industry consensus agrees on as workable. 1600gph would work great for your biofilter, but might be a problem for your bottom drain. I suppose you could run a hose through the BD pipe and vacuum out any sediment during your annual maintenance.