Help :(

[Ira]

It's frustrating that we have to go over this almost monthly. It's about as basic as "fire is hot" and explaining why a large object released 3 feet above your foot hurts more than just holding it.

Fishie, go get a gravel vac. Put it in your tank, start it siphoning. Now, plug the end, put the end at floor level, raise the end of it a few inches off the floor so there's a small loop below the end of the hose. Now, if the cannister filter had to push the water back up from floor level if you were to unplug the end of the hose the water would not move past the lowest point of the hose. Now, sit there and watch your carpet get soaked.

Before your tank drains empties completely all over the floor lift the end of the hose. See where the water level in the hose sits once you lift the end above the tank's water level? Surprise, it settles at the same water level as the tank. If it worked the way you thought, the water level in the hose would still be sitting down at floor level. But, no the weight of the water in the downward side of the hose pushes it back up the other side. All the cannister filter has to do is lift the water the height difference between the tank's water level and the outlet's water level!

And they have a max head height because that's the maximum head height they can pump. If it's 2 meters then they can pump up to 2 meters ABOVE THE TANK'S WATER LEVEL. NOT 2 meters above the level of the cannister filter!

[klaymann]

Wow .. you make it sound so clear for us simpletons .. so for a six foot tank have 8x 750 via aquas and you can create a 2 mtr water fall ..... cool 8) 8)

[klaymann]

And the subject of novembers discussion is ... " how can a canister pump 3 mtrs above a tank when the head height is only 2 mtrs ... lol "

[herefishiefishie]

Yes the water level trick is used in landscaping to check levels over a greater distance. Done this myself.

But the water level has nothing to do with a filter pumping water. Remember the water dosen't move until the filter is turned on. The impeller sucks the water into the canister,(like I said before not gravity) which travels through all the media & is the pressure of the impelleor not gravity pushes the water up the hose.

And the subject of novembers discussion is ... " how can a canister pump 3 mtrs above a tank when the head height is only 2 mtrs ... lol "

:lol:

Frenchy

[Freakyfish]

If the canister only had to push the water back up to the tank then a large canister would run out of water

Being a sealed unit it will suck the water down fast enough to keep up with the amount being pumped back in

There fore the pump is sucking the water down not using gravity

[Alan]

It really is only circulating the water.

As Ira said no easy work for it.

Alan 104

[herefishiefishie]

I was at dinner with a couple of fish people, we had a chat about this & yes views were split & varied :lol:

Been a great topic, now I have a few more people on a mission. :lol:

2 things that weren't answered by either side, one question lead to the other,

(a) If it is only circulating water, why is an impellor on a canister filter about the same size as an internal/submersible filter, when comparing lph.

eg; When my jebo canister impellor shaft broke, an internal filter from a different brand, same lph fitted perfectly. :-?

when

(b)Head height on a submersible pump is from the pump not the top of the water, why is then different in canister filters as stated by Ira?

I am yet to see anyone give me a link or prove that either way is right. I just would like to know for sure, Either way. I don't mind being wrong as long as I "know."

Good on one of my primary school teacher's for saying question everything. :roll:

Frenchy

[Ira]

(b)Head height on a submersible pump is from the pump not the top of the water, why is then different in canister filters as stated by Ira?

No, head height is NOT from the pump. It's from the surface of the water source. If it's sitting at the bottom of a tank it does NOT have negative head. It is NOT different.

[klaymann]

quote "(b)Head height on a submersible pump is from the pump not the top of the water, why is then different in canister filters as stated by Ira?"

Now that is a good question ... negative head ... hmm .. does that mean water source above pump unit .. or ....

[Ira]

http://www.pumpcentre.com/psdwg/statichead.htm

http://www.fluidedesign.com/tutorial2.htm

Static Head –

This is the vertical distance you raise the water. To determine your static head, measure from the surface of the pond (vertically), to the highest point in the discharge line where the water is discharged to the atmosphere. This is usually the top of your biological filter, or waterfall.

http://www.pondarama.com/html/the_right_pump.html

Read over all those webpages, look at the diagrams, if you still don't get it, it's time to give up.

[herefishiefishie]

Don't worry I never give up, :lol:

Cheers Ira, the sub pumps are stated from water level too, :oops: silly me. But what manufacters state relies on something called pressure. Which they don't state. :roll: Did you notice that?

Firstly;

I have noticed at work that different pond filters seemed to pump at different rates yet they have the same filter. :-? So I thought hmm, there must be a reason for this :-? and yep there is.

Reasoning;

To better understand what factors can affect the pump's flow rate, I first need to introduce the concept of pressure. What I was trying to get across from the start. :roll: Pressure is a force divided by the area that it is applied to, often quoted in pounds per square inch, or psi, for short.

Example;

A tray filled with a gallon of water an inch deep but 10" wide by 23" long would have a pressure on its bottom of about 0.037 psi (8.5 lbs / (area of tray bottom or 230 square inches). The same amount of water, but in a tube whose cross-sectional area is one square inch but 230" tall, would have a pressure of 8.5 psi on the bottom of the tube (8.5 lbs / 1 square inch). The reason for the different pressures, even though the weight of the water is the same in both cases, is that the weight is supported by a large area in the first example and so the force on any small section is low.

But, in the second example, all the water's weight is supported by a small area and so its effective pressure is correspondingly higher.

So please note,

Fact;

Consequently, the maximum head or water column height that a pump can support is really a measure of the maximum water pressure that a pump can produce. (so really its from the pump not water level)

How this relates to canisters?

Ira's link does state it is the impellor that moves the water.

The rotational motion of the impeller projects fluid particles

And height is one factor that effects the flow.

The pump will produce a certain discharge pressure corresponding to the particular conditions of the system (for example, fluid viscosity, pipe size, elevation difference, etc.).

With a canister filter the effective pumping height/flow rate as shown is measured from the water level in the canister filter,(the actual head of a pump is determined by the highest water level in the canister.)

I give up....

Frenchy

[Freakyfish]

I thought I would go & ask eheim(the best reputation for making canister filters)

I sent them an email asking that I have my canister filter on the floor directly under the tank, would I get an increased flow rate if I lifted the filter up, so to close the gap between canister filter & tank.

Yes Brad it definately will affect the performance of your filter if you reduce the head of the water and increase the height of the filter off the ground.

Regards

Nathan Patrick

To quote Frenchy, who am I to argue with them?

Brad

[herefishiefishie]

Debate Brad not argue. :roll:

I rang up a couple of sales reps to about this too. Both guys been in the industry for years & they said the same thing.

Yes Brad it definately will affect the performance of your filter if you reduce the head of the water and increase the height of the filter off the ground.

Regards

Nathan Patrick

Now eheim is the ducks nuts of this industry,(Brad has a canister from ehiem, his uncle used 20 years ago, still works today) I have now gone from I think I know, to really sure.

Frenchy

[Ira]

Of course decreasing the head will help, you guys just can't figure out what head IS! But raising the cannister will only help marginally because it's assumed you'd be shortening the hoses.

[herefishiefishie]

The original comment was in reaction to me saying you loose flow in a canister filter with the height pumped up a hose. As does media,bends in pipes....

Others says no it dosen't.

Ehiem who makes filters says it does make a difference, by shortening the distance,(hence the shortening of the pipe, never assume) increases the flow. Correct.

As have sales reps for companies that make these products.

That is the answer to my statement about flow rate.

Ira can you now take the arguement up with them thanks. Surely after decades of making them they would know.

Now if you look at the diagram,

At the sump,(bottom tank) see how the pump pushes the water up, the water flow starts from the top of the sump's water level.(depending on psi's) So water gets pushed up the pipe, once above the sump's water level its adding pressure. So by the time the water has reached the peak of the main/top tank the flow rate is lower.

A canister filter, similar in a way, the pump in a canister is at the top of the canister, which is also its highest water level. Head height stated on a canister filter is from the top of the canister.

The canisters are set up so the water flows down the canister from the tank. The reason for the water flow in the filter to be from the bottom up is that gravity will always be working to move the heavy particles down or helping to prevent the filter from clogging up. If the filter worked the other way, gravity would work to move the heavy particles deeper into our filter. This usually will result in reducing the water flow through the filter and rendering your filter less than optimal. Not to mention make your pump work harder and reducing its life.

Why is the flow rate rated from the top of the unit, because if you fill a canister with water using gravity, the media slows down the flow, have you noticed when filling a canister this way that the water only just fills the canister if that,& dosen't go all the way up the pipe as suggested by others.

If others were right why do canister filters then have primeing buttons, or detachments to fill the canister so the impellor can function properly

Frenchy

[Ira]

A sump and a cannister filter are two entirely different systems. A cannister is sealed. A sump is not. The head height of a cannister filter is the difference between the main tank's water level and the cannister's outlet level. The head height of a sump is the sump's water level to the pump's outlet above the main tank.

And don't assume because Eheim has been around for decades that the probably minimum wage monkey answering their emails has any clue what they're doing. That's as logical as saying that because animates has been around for a decade that bob in the fish department knows everything.

[Freakyfish]

Ira if a canister is different from a sump pump then how does your diagrams show anything at all

All your diagrams are not for a canister filters

Although there arent exactly a sump either they are not a sealed unit and they are not a canister

Also you make a valid point about Eheim but i dont think a major company would just let the base staff answer questions in writing as the chance of them being wrong would be to risky

wouldnt that be like agreeing with a moderator of a forum just because he is

Every single Rep for every single company i have talked to about canister filters has said the exact same thing

yet you disagree with the actual manufacturers

you would like to think the people who invented and made their money from them would know what they are talking about

Brad

[misnoma]

Brad.

This is physics.. not fishkeeping, simple as that.

Ira is utterly correct, in a closed system (like a cannister filter) the effective head between inlet and outlet is zero.

In an open system like a sump, yes, head is measured from the top of the sump to the top of the tank, but that's a totally different story.

Only difference moving the filter higher up (and shortening the hoses) will make is reduce friction in the hoses, and therefore allow a small amount of additional flow.

Some manufacturers claim is worthless unless they have facts to prove it. The diagrams Ira posted clearly show how things work.

[misnoma]

One way this hopefully will make sense to you.

Take one cannister filter

Take two hoses

Fill Hose (A) with water, connect one end to the inlet of the cannister filter, and put the other end in the tank. (sound like filter instructions yet? )

Take Hose (B) and attach it to the outlet of the cannister filter, put the other end in the tank.

Open the taps on the filter, watch water rush down hose (A), fill the filter with water.

Now.. does it stop there? No it doesn't... once the filter is completely full, our friend gravity will start filling hose (B). Note the filter is OFF, therefore no pumping is taking place, purely gravity pushing the water back UP the hose. (note, you may need to lift hose (B) out of the water to release any trapped air).

Once things settle, you'll notice that 1) the filter is now full of water, 2) Hose (A) is still full of water, and 3) Hose (B) is now full of water as well!

Hang on... we haven't used a pump, but... doesn't the pump need to LIFT the water... NO.

Equilibrium in a closed system is exactly this... water finds it's own level, and will move to equalise the pressure in the hoses, therefore the hoses both become full all on their own.

So.. if they can become full all on their own, what is the pump there to do? Simple.. overcome the friction of the filter media, and also the friction in the hoses and provide circulation.

[Freakyfish]

The water will not go up a hose to start the siphoning hence a canister will not fill it self up as you know it is looped over the tank edge

I agree that once siphoning starts the canister will fill up but i disagree that a canister will pump 10 storeys up as claimed earlier

I still stand by the comment that the maximum height is measured from the top of the canister to the top of the tank

The pressure of the column above the pump will reduce the flow as the filter media will have enough friction to negate the the water pressure coming down the outlet

This is as easy experiment grab any pump and a long hose and see how high it will still pump

Brad

[Alan]

Geeze FF

That's what Ira is bleeding well saying

When the upheld hose stops flowing that is it's max. head.

It gradually slows up (the flow) as it is lifted upwards and the height is increased.

Starting to wonder what other heads are on the other side of the ditch, or is it just too much sun??

Alan 104

[misnoma]

The water will not go up a hose to start the siphoning hence a canister will not fill it self up as you know it is looped over the tank edge

Hence I said fill the inlet hose with water.

I agree that once siphoning starts the canister will fill up but i disagree that a canister will pump 10 storeys up as claimed earlier

put the cannister filter 10 stories down, and the return hose back into the tank, and gravity will lift the water 10 stories for you, the pump doesn't have to do diddly squat.

I still stand by the comment that the maximum height is measured from the top of the canister to the top of the tank

The pressure of the column above the pump will reduce the flow as the filter media will have enough friction to negate the the water pressure coming down the outlet

Actually, the pressure of the column above the pump EXACTLY matches the pressure caused by gravity syphoning it out of the tank. The only thing the pump has to do is overcome the friction in the filter itself and the hoses.

This is as easy experiment grab any pump and a long hose and see how high it will still pump

Sure.. so long as the water coming into the pump comes from the same height as where your outlet is... remember a sump arrangement is totally different from a cannister filter.

[herefishiefishie]

It gradually slows up (the flow) as it is lifted upwards and the height is increased.

From Alan.

Thank you Alan, you answered what I said at the start.

Plus you loose litres per hour with the height.

From me.

Which is where this discussion started from.

Actually, the pressure of the column above the pump EXACTLY matches the pressure caused by gravity syphoning it out of the tank.

Really, I thought gravity had a constant force?

Don't canister filters all have different powered motors?

Plus don't forget gravity works down, if I drop a ball it don't bounce back up to the same height.I know standing water gives you a perfect level, we are talking about motion.

With a canister filter all the media slows up the flow, sub pump diagrams, have less friction.

It is the motor/impellor & gravity that works a canister.

put the cannister filter 10 stories down, and the return hose back into the tank, and gravity will lift the water 10 stories for you, the pump doesn't have to do diddly squat.

Then how come "EHIEM"(ever heard of these guys) stated this,

Yes Brad it definately will affect the performance of your filter if you reduce the head of the water and increase the height of the filter off the ground.

Now this answer was to the question, If I raise my canister off the floor & onto a stand, the canister is still under the tank.

Frenchy

[herefishiefishie]

Sun is great Alan. 8) Mid 20's "again" today, I have water ageing outside, lovely. :lol:

Better than grey, rain & cold.

Frenchy

[suphew]

Great example misnoma,

I'm sorry brad you are still wrong. To simplify your experiment to something every one could try. Take a length of hose, and a mouthful of water. put one end of the hose in your mouth and hold the other end straight up and try to blow the water in your mouth up it, hard work yeah? now hold the hose straight out, easy work yeah? Now hold the hose so it droops down but the out let end of the hose is still at the same level as your mouth, surprise, still just as easy.

The physics concept is a bit hard to get your head around, but the logic is simple. Unlike gases, liquids DO NOT COMPRESS, therefore if you push down (gravity) on a liquid, only 2 things can happen.

1) if it cant go anywhere it pushes back with an equal and opposite force, i.e. for a glass of water, gravity pushes on water, water pushes on glass, glass pushes on desk, each of these pushes back, desk push back on glass, glass pushes back on water... otherwise the water would fall through the glass, the glass through the desk.. etc

2) if it can go somewhere it will go there until another force balances it.

So in your cannister filter the water runs down the inlet hose (gavity is pushing it down right?), It fills up the canister, now if the out let hose of the wasn't in place (or was below the level of the tank) the water would run out, right? (This is negitive head, and you wouldn't need to pump water to make it move because gravity is doing the work for you.) If the out let hose is at the same level as the top of the tank the water keeps draining down the inlet hose until it fill up the outlet hose to the same level as the tank, yeah? So it is balanced, still with me? same force is pushing down on the inlet and out let hoses. Ok this is zero head! Now if the out let hose is above the level of the inlet, the water in the hoses is going to stay the same (as each other, i.e. still balanced) to get the water to go up the hose you have to add more force (positive head!).

Therefore if you inlet and outlets are at the same level the force is balanced, therefore it takes very little force to move the water!

Think about how much energy a cannister pump uses, like 7watts or something? To pump water from my sump (3 foot) to my tank and get around 700lph I'm using a 50watt pump. If I was using a 7 watt pump I would be lucky to get a dribble of water at 1/2 a foot.