Ira Posted February 16, 2012 Report Share Posted February 16, 2012 I've been meaning to do this for a while since everyone seems to argue that canister filters will flow more if you have them higher. These are tested with an empty old CF1200, measurements were made by running the filter into a bucket with the outlet hose at approximately tank water height. On floor: 2.5L in 15 seconds, 600LPH 1300mm from bottom of canister to tank water surface Middle: 2.5l in 15 seconds, 600LPH 600mm from bottom of canister to tank water surface Top: 2.4L in 15ish seconds, 576 LPH +80mm(Above) from bottom of canister to tank water surface Raising the filter 700mm made no difference at all in the flow. Putting the filter above started the filter sucking a little bit of air in and when I started the test it took a second to clear the air out and start flowing well. That's probably what lead to the lower flow at that height. A newer, more well sealed filter likely wouldn't have this issue. Also it would be a pain in the ass to prime the filter, so I wouldn't suggest having it above the tank. Quote Link to comment Share on other sites More sharing options...
blueether Posted February 16, 2012 Report Share Posted February 16, 2012 Thankyou for proving what I thought Quote Link to comment Share on other sites More sharing options...
kiwiplymouth Posted February 16, 2012 Report Share Posted February 16, 2012 Good Job, How about a trail with the intake in a bucket on the floor and the outlet in the tank then visa versa Quote Link to comment Share on other sites More sharing options...
blueether Posted February 16, 2012 Report Share Posted February 16, 2012 Lifting the water 1300mm would slow it down to at a guess about 1/3 of the "full flow" (the ~600 l/h as Ira measured) Max head on the cf1200 is quoted as 2m (When New) Quote Link to comment Share on other sites More sharing options...
CodKing Posted February 16, 2012 Report Share Posted February 16, 2012 Just out of curiosity, does a canister filter push or pull the water? Different models do it different ways? And would this make a difference? Good effort on the experiment! Quote Link to comment Share on other sites More sharing options...
Ira Posted February 16, 2012 Author Report Share Posted February 16, 2012 Just out of curiosity, does a canister filter push or pull the water? Different models do it different ways? And would this make a difference? Good effort on the experiment! Depends how you want to look at it. Could argue that no pump can pull water. They push water creating a void which ambient pressure pushes more water in to fill. Quote Link to comment Share on other sites More sharing options...
blueether Posted February 16, 2012 Report Share Posted February 16, 2012 The aqua-ones create a negative pressure inside the canister, dont know about other makes Quote Link to comment Share on other sites More sharing options...
Hamstar99 Posted February 16, 2012 Report Share Posted February 16, 2012 i guess all central fugal pumps are designed to push water rather than pull it. Quote Link to comment Share on other sites More sharing options...
GrahamC Posted February 17, 2012 Report Share Posted February 17, 2012 Is it possible or meaningful to measure the current draw in the different positions? Just wondering if it has to do more work below the tank level because of the two columns of water in the hoses, and the effect of gravity. Quote Link to comment Share on other sites More sharing options...
alanmin4304 Posted February 17, 2012 Report Share Posted February 17, 2012 The work it has do do by pushing the water in the outlet is compensated for by the help it is getting from an equal column of water siphoning into the inlet. Quote Link to comment Share on other sites More sharing options...
livingart Posted February 17, 2012 Report Share Posted February 17, 2012 Quote Link to comment Share on other sites More sharing options...
Warren Posted February 18, 2012 Report Share Posted February 18, 2012 Ira is 100% correct. The only thing that matters is the pressure difference between the inlet and outlet. Since both are more or less at the lame level the energy required to move the water is exactly the same irrespective of how far the filter is below the water level. You could even take the filter above the water level once it's running at it would still work and use exactly the same energy. Go research the laws of physics and it will all become clear... The only thing that changes by moving the filter height is the pressure inside the filter. lets just put this one to bed :roll: Quote Link to comment Share on other sites More sharing options...
blueether Posted February 18, 2012 Report Share Posted February 18, 2012 "The only thing that changes by moving the filter height is the pressure inside the filter" Correct me if I'm wrong here,but as water is a non-compressible liquid, the canister stays the same volume and the flow stays the same surly the (-ve [in most filters]) pressure in the filter stays the same? Quote Link to comment Share on other sites More sharing options...
Warren Posted February 18, 2012 Report Share Posted February 18, 2012 Pressure is proportional the the height of water. In this case it's the height of the water in the tank to the height of the filter. Get enough height between the tank water level and the filter and it will burst. If the filter is below the tank it will have pressure in it. If it's above the tank it will have negative pressure as long as both pipes are under water. If one is above the water and it's turned off, all the water in the filter and pipes will siphon back into the tank. If you don't believe me just get a hose and create a siphon out of your tank. If you lower the end of the hose the pressure on you finger get higher - just try it (it's only physics)... Quote Link to comment Share on other sites More sharing options...
hovmoller Posted February 18, 2012 Report Share Posted February 18, 2012 Love a good experiment... Thanks Ira Quote Link to comment Share on other sites More sharing options...
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