Do canister filters lose flow with head?

[mgk]

since we can all agree that sumps lose flow with head height i will use that as an example...

a sump pump needs to work 100% against gravity because it is the only thing pushing the water up to the tank..

a canister doesn't.. the vacuum in the canister allows for the water to be pushed up to the waterline thus making the pump have to work less.. at any height below the tank's waterline the sump will always have to work to push the water in the tube up to the tank, but the pressure from the inlet will always be counter acting the difference in the output..

if you look at a u shaped tube u can see what im talking about.. no matter how much u fill it the water levels will always be equal. if desired ill even take a video of my canister's outflow as i move the canister up and down.. the flow rate wont change..

I understand what your talking about but head loss also takes into effect the bends and friction loss in the tube.

head loss even occurs in a siphon.

on this video http://www.youtube.com/watch?v=hdjv_6mPhtM&feature=related
at 1:39 the headloss is the reason they make the suggested maximum lenght.

 

[LD50]

you still have to fight gravity, it is easier to pump water in that vacuumed state with the water level being high but you still have to do work to move water in the hose. The water doesn't want to move.

also head loss takes into account friction in the hose.

you can go to homedepot and buy 20 feet of hose to test it out.

Fighting the hoseing yes, but fighting the gravity of a vertical asscent? not quite. Given all things are equal (tube length/size/height etc) gravity will exert the SAME force on the water flowing in as it dose on the water being pumped out. Which means gravity will cancle its onwn effects by helping the filter take in water with the SAME force it tries to slow the filter down on the output side. Yes it has to fight tubeing but the gravity feed will keep a canister from having to fight gravity the way a sump pump dose. Gravity, not what slows a canister down. The hoseing yea it effects it some, but the media is what really impacts a canisters performance. Esp considering most people on MFK only clean their canisters out once every blue moon and then wonder why no matter how many WC's they do their NO3 wont go down, with MONTHS of waste build up in their FX5 lol.

 

[Egon]

^^^ True.

I think the discussion is on the gravity part of head loss. Lets say you had the exact same pump and length of pipe so everything is the same. One system is an open type sump system and the other filter is a closed loop canister system. With everything else equal for the sake of this argument the closed loop will have more flow because it's not fighting gravity (as much) as the open loop.

 

[Egon]

Fighting the hoseing yes, but fighting the gravity of a vertical asscent? not quite. Given all things are equal (tube length/size/height etc) gravity will exert the SAME force on the water flowing in as it dose on the water being pumped out. Which means gravity will cancle its onwn effects by helping the filter take in water with the SAME force it tries to slow the filter down on the output side. Yes it has to fight tubeing but the gravity feed will keep a canister from having to fight gravity the way a sump pump dose. Gravity, not what slows a canister down. The hoseing yea it effects it some, but the media is what really impacts a canisters performance. Esp considering most people on MFK only clean their canisters out once every blue moon and then wonder why no matter how many WC's they do their NO3 wont go down, with MONTHS of waste build up in their FX5 lol.

X2

 

[Weaksrt]

it is just like in a car the speedo in a car is upto 10% slower then the speedo so if you got a ticket and the speedo of a car said you were doing the speed limit the manafacturer is lieable.
it is the same with pumps it may say 2000 gallons per hour but it might do 2200.
in conclusion your pump should be doing about what it says it does.

This is only true if every pump in the world is Overrated for there outputs.

I know other Products in the world say they do what they do but not to the full scale of thing but within the realm of Pausable Deniability. They can assume they do what they do but maybe a +/- to the Manufactures Specs. There is always a Tolerance from One Manufacter to another.

 

[dawnmarie]

Given all things are equal (tube length/size/height etc) gravity will exert the SAME force on the water flowing in as it dose on the water being pumped out. Which means gravity will cancle its onwn effects by helping the filter take in water with the SAME force it tries to slow the filter down on the output side.

I recently had a lengthy exchange with Chompers(author of the sticky Pipe Sizing Charts and Flow Rates ) on exactly this subject. He gave the same answer as LD50. I offered the thought that if you used his chart and oversized the drain compared to the pump that the pump would see a net gain. He basically told me that if this was so then I had perfected perpetual motion.

 

[jschall]

I understand what your talking about but head loss also takes into effect the bends and friction loss in the tube.

head loss even occurs in a siphon.

on this video http://www.youtube.com/watch?v=hdjv_6mPhtM&feature=related
at 1:39 the headloss is the reason they make the suggested maximum lenght.

Yes, there are frictional losses through lengths of hose, but head height refers to the difference between the intake and outlet water levels. Since a canister filter has its intake and outlet in the same body of water, the head height can be considered 0.

The reason they say not to put the canister too far below the aquarium is because the water pressure at that depth can cause the canister to leak.
Imagine a hose filled with water, attached to a water balloon on one end and an aquarium at the other. As you lower the water balloon, it will increase in size and eventually explode as the pressure gets higher. Same goes for the canister.

 

[jschall]

I recently had a lengthy exchange with Chompers(author of the sticky Pipe Sizing Charts and Flow Rates ) on exactly this subject. He gave the same answer as LD50. I offered the thought that if you used his chart and oversized the drain compared to the pump that the pump would see a net gain. He basically told me that if this was so then I had perfected perpetual motion.

Yep, perpetual motion schemes usually come from a misunderstanding of fluids or permanent magnets.

 

[dawnmarie]

Yep, perpetual motion schemes usually come from a misunderstanding of fluids or permanent magnets.

There is one other source.

The search for mechanical perfection.

It's what keeps us motorheads always looking for ways to improve our combinations.
My wife calls them "meaningless incremental improvements'
I call them free horsepower.
It even applies to the mechanics of aquaria.

 

[Toby_H]

If you set up a canister filter with no media at all in it... prime it and get it running... then turn it off....

Next lift the return line so air can enter the end...

The water level in the return line will balance out to the same level as the aquariums water...

Thus verifying... a properly set up canister filter has almost no head pressure. The head pressure will be the distance from the water level in the tank to the point the return line crests the lip of the tank...


Jschall... That was a great description above of why it is suggested canisters should not be placed lower than X below the aquarium...