Thread: Skimmer and bottom drain into one filter

Those who are running both bd and skimmer into a drum or sieve, how do you balance the flow form the skimmer and from your bd,, is it simply a case of gagging the skimmer/bd line with a valve, I remembered when I first built my pond I had a go at linking both pipes into a diy filter and virtually had to shut the bd to get the skimmer to work, I’m guessing the extra pressure on the bd with the weight of water meant that was always going to give the most flow?

Originally Posted by Paul burt

Those who are running both bd and skimmer into a drum or sieve, how do you balance the flow form the skimmer and from your bd,, is it simply a case of gagging the skimmer/bd line with a valve, I remembered when I first built my pond I had a go at linking both pipes into a diy filter and virtually had to shut the bd to get the skimmer to work, I’m guessing the extra pressure on the bd with the weight of water meant that was always going to give the most flow?

Correct, I think.

On gravity set ups the flow through the filter is dictated buy the pump removing water from the filter and creating a small head difference, the water them flows in under gravity - hence gravity set up. The more you pull out the more will rush in. Water, being water, simply takes the easiest path. Very rarely are all the feeds (bd, skimmer etc) balanced so often one feed will dominate as you've found out. By putting in valves you'll be able to cause restrictions in the pipework and allow it to balance. This should allow you to "tweak" the flows so you get the flows you are looking for.
Ideally use ball valves, more expensive but significantly more reliable and easier to fine tune.

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Originally Posted by Paul burt

Those who are running both bd and skimmer into a drum or sieve, how do you balance the flow form the skimmer and from your bd,, is it simply a case of gagging the skimmer/bd line with a valve, I remembered when I first built my pond I had a go at linking both pipes into a diy filter and virtually had to shut the bd to get the skimmer to work, I’m guessing the extra pressure on the bd with the weight of water meant that was always going to give the most flow?

Er, No.
The pressure is the difference between the surface of the pond and the water level in the filter, which is the same for both. The fact that some of the water goes via the BD does not change the pressure at the filter, i.e. the static head is the same.
You may get much better flow through the BD because of factors like larger pipe diameter, different pipe material, fewer bends, i.e. the dynamic head is less, so the flow rate is better.

Your skimmer may have the same pipe diameter and the same number of bends, but the water is coming over a weir that may mean the film of water is only say 5mm deep. Multiply that by the width of the weir and you get the effective area of the inlet. Compare that with the area of your pipe and you may find it is significantly less, so the flow rate will be much lower, all other things being equal.

Pulling more water through your filter will lower the water level, increasing the static head, pulling more from both skimmer and BD. This greater flow may well pull the weir down further, increasing the depth of water over the weir, and thus increasing the effective area. Your flow through the skimmer may improve more than the flow through the BD.

You could try removing some of the foam on the back of the weir so that it does not push the weir up with as much force, allowing a thicker film of water over the weir.