# Effect of changing pipework diameter



## jameson_uk (8 May 2019)

Theoretical at the minute but I was looking at a filter which has 8/12mm pipework.  There is some 10mm outflow glasswork around but very few 10mm inflows.

This got me wondering what the impact would be of using 12/16mm pipework with an adaptor at the filter....

I am guessing the inlet shouldn't make much difference as it is gravity fed and under pressure so the flow is going to be determined by the pump?

Outflow though has me confused.  I get that a pump running at the same throughout is going to displace the same amount of water but would the weight of water trying to go back the other way mean the pump wouldn't be able to push as much water?


----------



## foxfish (8 May 2019)

All water pumps will have a maximum head rating, in other words... how high the pump will pump water before it can no longer pump against the water pressure above.
Certain pumps are designed to work against high pressure, they tend to be high wattages and have different shape impeller that scoops water.
The inlet diameter is equally important as the outlet, generally speaking the inlet will be larger than the outlet.
Most of the pumps we use are...  low pressure ... low wattage .... pumps and are easily effected by any form of back pressure.


----------



## sparkyweasel (8 May 2019)

Remember that if your intake and outlet are both submerged in the same tank, the head is zero. If your outlet is above the water surface, the head is the height from the surface to the outlet, everything else levels itself, doesn't use pump power.


----------



## jameson_uk (9 May 2019)

So 50/50 then so far 

Does anyone do this?


----------



## Edvet (10 May 2019)

sparkyweasel said:


> Remember that if your intake and outlet are both submerged in the same tank, the head is zero


I've heard that more times, still dont believe it. I am sure having a canisterfilter ( Eheim usually) next to the tank yielded more flow then having the canister on the floor ( same hoses attached)( tank on stand), hence the max height settings on the eheim litterature.
(https://www.eheim.com/resources/product//212/downloads/11/EHEIM_classic_150_manual.pdf).


----------



## zozo (10 May 2019)

jameson_uk said:


> This got me wondering what the impact would be of using 12/16mm pipework with an adaptor at the filter....



Absolutely no impact, if it is only on te inflow it actualy would benefit having more vollume at the input/suction side of te pump. Because the suction is the opposite force of the head pressure pushing.it out and up again at the other side. Thus having larger diameter/volume at this suction side results also in more volume/mass syphoning down (gravity) to the pump actualy resulting in a positive effect.

You probably will lose a little head pressure at the outflow with a bigger diamter because the pump now has to push more volume/mass up. Theoreticaly the capacity doesn't change very much, there will be a little less jet stream at the outflow with a larger diameter hose. But in volume what comes out still be approximately the same. Simply explained 8mm² jetstream is longer than 10mm² jet stream both having same volume in mm³

This might impact the overall flow in the aqaurium, this is hard to predict.

But i assume you want to use a 8/12mm Outflow and a 10/12mm inflow = No or Possitive impact.


----------



## Tim Harrison (10 May 2019)

sparkyweasel said:


> Remember that if your intake and outlet are both submerged in the same tank, the head is zero.


I suppose by definition it's true in so much as the pumps energy is supposedly used to just circulate the water. But I think I get where Ed is coming from.

My understanding of physics is rudimentary to say the least...but if the desired flow is greater than that generated by gravity isn't the pump still going to have to generate head especially since water is a compressible fluid, and doesn't friction against pipe walls also have to be taken in to account ?


----------



## zozo (10 May 2019)

Tim Harrison said:


> and when friction against pipe walls is taken in to account ?


Very dynamic, dirty hoses can significantly reduce flow or negatively impact head pressure. I'm sometimes slopy with cleaning hoses and experience quite some difference when its clean again..

But Head pressure is water column mass in height.. Or can be converted in actual pressure with 10m water column is 1 bar despite the volume. Resulting always in a head if the pump is placed lower than the output.


----------



## ian_m (10 May 2019)

zozo said:


> this suction side results also in more volume/mass syphoning down (gravity) to the pump actualy resulting in a positive effect.


Nope not true. Gravity has absolutely no effect in a closed loop circulation in a canister filter situation. Gravity & syphoning only come into effect when the lower end of a pipe is open to atmosphere, which in a canister filter it is not.

The pump in a cannister filter has only got to overcome the water resistance due to the filter media and piping, it does not have to overcome gravity at all. This is why reducing the amount of filter media, length of piping and keeping piping clean increases the flow rate as these are the things the pump has to overcome, the pump does not have to overcome gravity.


----------



## zozo (10 May 2019)

ian_m said:


> Nope not true. Gravity has absolutely no effect in a closed loop circulation



If you say so..  I can only take your word for it.. But as far as i know Mass and gravity can not be shut out.. It's always there open or closed..

Take a Central heating system that is trully closed.. Make it 10 meter high and connect a pressure gauge at the lower end and one at the top. Fill it till 2 bar at the gauge at the top.. Go 10 metre down look at the guage and it will show you 1 bar more, showing 3 bar in this case since its 10 metre down.

If that aint gravity and mass, i most be in the wrong dream..


----------



## ian_m (10 May 2019)

zozo said:


> If that aint gravity and mass, i most be dreaming something else..


Sorry looks like dreaming....again..... The head height is only relevant if both ends of the system are open ie you are pumping water from a bucket on the floor into your tank. A cannister filter and CH system are closed systems and pumping head height is not really relevant as the head height between inlet and outlet is zero.

Obviously a pump with greater open end head height will pump more water in closed system, as pump is likely to be more powerful, but as the head height in a cannister filter in a fish tank is zero, the head height can be a useful indicator of "pump capability".


----------



## zozo (10 May 2019)

ian_m said:


> A cannister filter and CH system are closed systems and pumping head height is not really relevant as the head height between inlet and outlet is zero.



I get it.. As in the law of communicating vesels. That is actualy what a canister filter setup is with in and outlet at same level and a pump at the U bottom end more or less. If both ends are same lenght.. Still need gravity for that, to equal out te mass... But indeed i was dreaming. . Thanks for the wake up call..


----------



## jameson_uk (10 May 2019)

ian_m said:


> The pump in a cannister filter has only got to overcome the water resistance due to the filter media and piping, it does not have to overcome gravity at all. This is why reducing the amount of filter media, length of piping and keeping piping clean increases the flow rate as these are the things the pump has to overcome, the pump does not have to overcome gravity.


Do you really mean volume of piping or is it literally the friction against the pipe wall?

I guess the main question here is would I be OK running 12/16mm pipework on both both inlet and outlet (via adapters) into a filter that takes 8/12mm pipework?


----------



## ian_m (10 May 2019)

jameson_uk said:


> Do you really mean volume of piping or is it literally the friction against the pipe wall?


Friction on dirty walls of pipe. You will be devastatingly surprised how much your filter flow rate increases when you brush out the filter piping. I use a JBL Cleany, I got for a couple of quid 2nd hand on Ebay.
http://www.jbl.de/en/products/detail/2457/jbl-cleany



jameson_uk said:


> I guess the main question here is would I be OK running 12/16mm pipework on both both inlet and outlet (via adapters) into a filter that takes 8/12mm pipework?


No problem should not affect the filter flow rate....However it will reduce the water velocity on the outlet, as the flow rate in 12/16mm will be slower than that of 8/12mm, so that flow in the tank might not get so far around the tank. 8/12mm outlets would be ideal, but can't see why you shouldn't try 12/16mm.

You might be able to bond, using PCV glue, the 16/12mm onto the outside of 12/8mm, seen it done many times, so that you don't have to use slight flow reducing barbed pipe reducer whose internal diameter may be as small as 6mm. Search Ebay for "barbed reducer". Remember to put jubilee clips on the attachments to prevent accidental "unplugging"...voice of experience here...its amazing how much water can syphon onto the floor from an "unplugged" 22/16mm pipe...


----------



## jameson_uk (10 May 2019)

ian_m said:


> Friction on dirty walls of pipe. You will be devastatingly surprised how much your filter flow rate increases when you brush out the filter piping. I use a JBL Cleany, I got for a couple of quid 2nd hand on Ebay.
> http://www.jbl.de/en/products/detail/2457/jbl-cleany


No I wouldn't I cleaned out the inlet and outlet pipework last weekend and you can really see the difference... 



> No problem should not affect the filter flow rate....However it will reduce the water velocity on the outlet, as the flow rate in 12/16mm will be slower than that of 8/12mm, so that flow in the tank might not get so far around the tank. 8/12mm outlets would be ideal, but can't see why you shouldn't try 12/16mm.
> 
> You might be able to bond, using PCV glue, the 16/12mm onto the outside of 12/8mm, seen it done many times, so that you don't have to use slight flow reducing barbed pipe reducer whose internal diameter may be as small as 6mm. Search Ebay for "barbed reducer". Remember to put jubilee clips on the attachments to prevent accidental "unplugging"...voice of experience here...its amazing how much water can syphon onto the floor from an "unplugged" 22/16mm pipe...


The thought about needing 12/16 was that I wanted to attach the filter to a spin pipe to reduce the flow in the tank so that wouldn't be an issue.    The only thing would be whether the reduction in flow would be enough to stop the spin pipe doing what it needs to do (and I really cannot figure out the physics for that....).  The Viv spin pipe lists a flow of 10 lpm (http://www.viv.com.hk/gfilter.html#spin) and I was thinking of running at 300 lph filter so now sure if even that would be already to get the spin pipe working.   Only one way to tell.......  (Just don't tell the wife if I spend more money )


----------



## sparkyweasel (10 May 2019)

Edvet said:


> I've heard that more times, still dont believe it. I am sure having a canisterfilter ( Eheim usually) next to the tank yielded more flow then having the canister on the floor ( same hoses attached)( tank on stand), hence the max height settings on the eheim litterature.
> (https://www.eheim.com/resources/product//212/downloads/11/EHEIM_classic_150_manual.pdf).


Eheim states that is for "operational safety", not flow rate. 
Perhaps they test the seals etc for leaks to a certain pressure, maybe test at 2m so they're confident to recommend 1.8m max.


----------



## jameson_uk (17 Nov 2020)

I ended up getting a 10mm inflow and it was working pretty well (although it manages to suck in the betta's tail and he didn't make it).

This was a little glass inflow with a few slots. Yesterday whilst cleaning the tank I managed to not attach the outflow pipe properly and after a bit of a wiggle the pipe came off and water was spraying out. Cue panic and luckily as I had been cleaning the filter I had a bucket to hand so there wasn't too much mess.

In my haste however I managed to knock the inflow on the tank and cracked it right down the middle.

I replaced it with the stock inlet that came with the filter (just a standard plastic pipe with a little strainer) and this seems to have massively increased the flow. Still on the same pipework but is definitely much stronger than it was with the glass on. Surely these glass inflows can't restrict flow that much? And even so would restricting the flow (well amount of water reaching the pump) be the same as when reducing the pipework diameter?


----------

