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Discussion Starter · #1 ·
Well I bought an eheim 2217 because I am so used to buying much larger filters than I need from keeping SW and cichlids. I now realize 264 in a 25cube is a little insane. I have lily pipes. I haven't filled my tank yet; however, I wanted to know if throttling down the flow with one side of the output double tap will really cause back pressure on these filters. I see numerous posts on different forums where people swear by this method of reducing flow. Would it also benefit replacing it with a 2215 impeller? I am running an inline heater and diffuser...but nothing to really obstruct flow. I seem to worry more about the actual force created by the canister than the actual flow. If I do throttle the output do I just use one side of the output or both levers(canister side of the double tap or output line side of the double tap)?
 

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FWIW I have a 2213 on a 12g Long and have one of the levers throttled about halfway back on my outflow and haven't noticed any extra strain or abnormal sounds coming from the filter. It has been like this for over a year.
 

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There is a really large amount of bogus information passed around so we have to do some real filtering.
Strain on motors is often mentioned but that is old thinking. As I understand "strain", it would mean the motor was called on to do more than designed. So if you have a traditional motor, it has several things that the mag drive motors we use don't have. Take a sump pump as an example. It has a fixed impeller on a shaft, connected to a large moving part made up of metal wires wrapped on a core. These windings are fed current through a set of brushes and do carry electrical power. This is a standard type motor.
When you overload and slow down this motor, the cooling is reduced. A funny electrical thing happens as wires warm. They begin to carry more current. More current produces more heating. You've got a basic death spiral and the motor burns out when the wire insulation melts.
A mag drive has no brushes and no wires on the moving part connected to the impeller. So if you overload or even stop the impeller, there is no major increase in heat, no increase in current and no death spiral. There is a slight increase in heat due to the water flow stopping but as long as the motor is setting in water, that heat can't get very hot until all the water is turned to steam and gassed off. Not really even a thought when you just cut the flow through a canister filter.
If your water going through the filter gets up over two hundred degrees so that it steams, you do have problems but the filter will be one of the smaller things to worry about!
Reason for turning down the output is that turning down the input may make the impeller cavitate and that makes noise.
 

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Discussion Starter · #5 ·
Thanks guys hoorah! I was thinking if I ever upgraded at least I could use the filter on a bigger tank. It is easier usually to decrease than increase :) ...btw Rick thank you for the in depth explanation of the motor workings. An educational experience for sure.
 

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Hope it helps a few that still have questions. There are short answers to a lot of things but without having the background for why, I have a harder time remembering stuff. Next time you get around a small motor that has the right type frame so that you can see inside, you may notice a bunch of sparking at one end of the motor where the brushes ride on the moving part to carry the current across. That type will burn out in pretty short order if they get jammed.
 

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Discussion Starter · #7 ·
So for you eheim users that throttle the output...do you use both sides of the double tap or just one side?
 

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I've never found the need to throttle one down but logic says that it could be done any of three ways. First cutoof, second cutoff or both just a smaller amount so that the restriciton equals what you want.
Before somebody jumps up to show a different way, I might mention that there is a firm reason not to do this type action in other places ball valves might be used.
Nothing that would ever change what we are talking about but if you were dealing with a three inch water line and left a ball valve half closed for several years, it can erode and damage the edge of the ball so that it requires replacement. But that type of erosion does not come from a filter setup!
 

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Instead of throttling down I've had awesome luck drilling extra holes in the spray bar or enlarging the existing holes.. Creates a nice light flow
 
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