# Estimate flow loss when reducing pipe diameter?



## kilnakorr (16 Apr 2020)

I'm looking for your estimate (or calculations if you want to) on the flow loss when switching 19 mm pipe with 16 mm pipe on a canister filter?

I know there are some unknown variables like filter power etc. But just want your rough estimate.

Say a canister filter rated 2000 lpr with 19 mm pipes, would run how much with 16 mm pipes?


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## Zeus. (16 Apr 2020)

kilnakorr said:


> I'm looking for your estimate (or calculations if you want to) on the flow loss when switching 19 mm pipe with 16 mm pipe on a canister filter?



Thats a *big* ask as theres a hit with 19mm pipes - head of water, length of pipes, bends, filter media, pump to start with 



kilnakorr said:


> But just want your rough estimate.



Less - dependant on head of water, length of pipes, bends, filter media, pump 

I wouldn't give an estimate


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## rubadudbdub (16 Apr 2020)

Hagen Poiseuille equation will tell you the principles.  I've tried to fit your numbers to the equation, but maths isn't my strong point. An abbreviated version:

Flow =  Pi x pressure gradient x radius ^4
              --------------------------------------------
              Constant x viscosity x length tube

Flow varies proportionally to Pressure gradient along the tube, and to the radius of the tube raised to the power of 4.  More pressure or bigger tube = more flow

It varies inversely to length of tube and viscosity of the fluid. Long tubes and viscous fluids will restrict flow.

So radius has a big effect, due to it being raised to the power of 4.

The maths in your case is the bit I'm not sure about.  If diameter is 16mm radius = 8mm.  I'll save you some boring bits but comparing 8^4 = 4096 vs 9.5^4 = 8145

The ratio is ~ half, so if all other factors remain the same then flow should also be halved.  But I'll admit that seems a big drop in flow for loosing 3mm off a 19mm diameter. 

Also, Surface area of 16mm pipe 200mm2 vs 280mm2 for 19mm, by my calculation. This doesn't relate to the HP equation but will give you a rough idea that internal resistance will increase and reduce flow. 

Hopefully someone with better maths will come and clarify. 

Overall, I'd not be suprised if you lost at least a third of the flow, although my fag packet maths suggests half. 

If you must use 16mm pipe, you can mitigate the flow drop to some extent by:
1. reducing the length of the tube to a minimum
2. maximising the pressure along the tube by raising the filter up and reducing losses due to water head pressure.


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## kilnakorr (17 Apr 2020)

Zeus. said:


> I wouldn't give an estimate


I know it's quite an impossible question to answer. Was hoping someones experience could give me a hint.



rubadudbdub said:


> Overall, I'd not be suprised if you lost at least a third of the flow, although my fag packet maths suggests half.


That's a big loss. True the total hose area is roughly 1/3 less from 16mm to 19mm. 

Question is what canister to use:
2000 lpr using 19 mm hoses hooked up with 16mm hoses.
or
1700 lpr with 16 mm hoses.

I wonder how big a difference there will be between these two options.


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## papa_c (17 Apr 2020)

I would always go with the original design recommendations, as there would have been some extensive testing during development.

However if you already have the 19mm filter you could always mock up the reduction and test the output.


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## kilnakorr (17 Apr 2020)

papa_c said:


> However if you already have the 19mm filter you could always mock up the reduction and test the output.


I'm currently running with this.
However, looking at the option to replace it. My problem is trying to figure out if it will make any difference. If not, it will just be a waste of money.


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## rubadudbdub (17 Apr 2020)

papa_c said:


> you already have the 19mm filter you could always mock up the reduction and test the output.



... and then tell us please. I'm sure lots of people would be interested.

If you step down from 19 to 16 it makes sense to me to keep the 16mm section as short a length as possible.


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## foxfish (17 Apr 2020)

Why would you want to do this?


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## kilnakorr (17 Apr 2020)

rubadudbdub said:


> If you step down from 19 to 16 it makes sense to me to keep the 16mm section as short a length as possible.


Sure. As mentioned, I also have a lot of equipment connected to the filter, which further reduces flow.
Most of the equipment runs 16mm, so cannot do much 19mm. The intake is also reduced to 16mm.

I just (2 min ago) ordered a 1850 lpr filter that uses 16mm hoses. So taking my chances. Will pick it up Tuesday.
I can do a little visual testing on the flowrate on current and new filter as I'll be using the same hoses. Might even test how long it takes to fill an x liter container for some real data.


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## rubadudbdub (17 Apr 2020)

kilnakorr said:


> Question is what canister to use:
> 2000 lpr using 19 mm hoses hooked up with 16mm hoses.
> or
> 1700 lpr with 16 mm hoses.


Do you already have some 16mm fittings/glasswork that you want to use?

If you are trying to compare different brand filters then I'd caution against assuming that the flow rates will be comparable anyway.   The differences between manufacturers stated vs actual flow rates may well make any vaguely scientific comparison mute.


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## rubadudbdub (17 Apr 2020)

This was in PFK a while back.  It gives you an idea of expected differences between stated and observed flowrates for various head heights.


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## Jayefc1 (17 Apr 2020)

Pump 2litre from a bucket to another bucket with the two diffrent tubes time them.and you will see the reduction in flow


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## kilnakorr (17 Apr 2020)

rubadudbdub said:


> If you are trying to compare different brand filters then I'd caution against assuming that the flow rates will be comparable anyway. The differences between manufacturers stated vs actual flow rates may well make any vaguely scientific comparison mute.


Very true. Which is why deciding what to do in my case was difficult.
I do believe I will se an increase in flow going from my current cheap brand with small hoses rated 2000 lpr to eheim with standard hoses rated 1850 lpr.



Jayefc1 said:


> Pump 2litre from a bucket to another bucket with the two diffrent tubes time them.and you will see the reduction in flow


Yes. Once I've done a test with full setup, and switched filters, I can easily test the current pump with 19mm and 16mm. I can even try with various length hoses and heights to make a dataset.*getting my nerd mode on*


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## ian_m (17 Apr 2020)

This is how you connect smaller diameter "devices" (diffuser below) in a larger pipe. This is Zeus's from his tank. https://www.ukaps.org/forum/threads/olympus-is-calling.43046/page-3#post-475073 





The bypass allows flow around the diffuser, with the valve controlling the amount flowing in the bypass.


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## kilnakorr (17 Apr 2020)

ian_m said:


> The bypass allows flow around the diffuser, with the valve controlling the amount flowing in the bypass.


Thanks for the input. I do have experience with a bypass and did run one with a CO2 reactor some time ago.
The pipework that goes through my tank and my reactors are all 16mm, so it is not possible in my situation. Also, what I need is the flow through my equipment, not just return it to the tank.


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## kilnakorr (22 Apr 2020)

So...
I just installed the eheim 2078 (1850lpr).
It can't run both of my reactors and uv filter at full power 
Only 3 of 6 steps, whatever flowrate that means (50%?).
Did seems like more flow in the reactors.
I removed one reactor, which was only needed because of previous low flow, and the eheim picked up a bit. Still cannot get full power, but quite a flow in the reactor
Now I'm just checking to see if I can get a decent ph drop without a huge gas buildup in the reactor. If possible, then I'm making a bypass to get the full flow and filtration out of it


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## Zeus. (22 Apr 2020)

kilnakorr said:


> huge gas buildup in the reactor



my reactors do get a a lot of CO2 build up and they are low flow, but still get the pH drop and keeps them quiet as well


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## kilnakorr (22 Apr 2020)

@Zeus.  A little build up is fine, but don't want that loud splashing sound

It's a pretty large reactor, just hoping the flow is enough.
Would splitting the output between reactor and uv have an effect? It would reduce hose length on the reactor, but total it would likely be more.


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## Zeus. (22 Apr 2020)

kilnakorr said:


> Would splitting the output between reactor and uv have an effect?



Yes the flow in the reactor and UV filter would decrease dependant on the fittings and their would be an increase in the total flow dependant on the size of the fittings used. I oversized my fittings to has the least amount of increase in resistance so less drop in output.

You do get better CO2 uptake in a reactor thats at a higher pressure, but that has a bigger impact on the flow/output and puts more strain on the pump also.


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## zozo (22 Apr 2020)

The best rough estimate to get, give it a try, take 1-litre cup and a stopwatch...


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## kilnakorr (22 Apr 2020)

Zeus. said:


> Yes the flow in the reactor and UV filter would decrease dependant on the fittings and their would be an increase in the total flow dependant on the size of the fittings used. I oversized my fittings to has the least amount of increase in resistance so less drop in output.


Fittings are pretty much fixed, so can only change a few. I have roughly 40 cm pipe also, that cannot be changed unless I remove soil from the tank.



zozo said:


> The best rough estimate to get, give it a try, take 1-litre cup and a stopwatch...



True, but really don't want to mess with all the plumbing

It seems that it has picked up the flow. Guess it just needed to vent a bit.
PH has dropped nicely without a gas build up in the reactor

Going to try a diy spraybar and see if I like the flow and don't mind the look. Guess the filter will tell me if flow decreases. Guess that's a plus


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## zozo (22 Apr 2020)

kilnakorr said:


> True, but really don't want to mess with all the plumbing



The issue with formula is next to a load of others you need to know the Pump Pressure. Yet not seen aquarium filters/pumps specify this...

But if you like to have a go at it.
https://en.wikipedia.org/wiki/Hazen–Williams_equation

Some pump suppliers have online calculators based upon Hazen Williams Model.
Yet i didn't find any in English... But a guess is it must be out there somewhere. I wouldn't know the proper English search query for you to find it. Pipe line capacity calculator? Maybe..


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## kilnakorr (22 Apr 2020)

zozo said:


> The issue with formula is next to a load of others you need to know the Pump Pressure. Yet not seen aquarium filters/pumps specify this...


Very true.

I actually think, I just need to calm down.
I don't have any major issues, just want a slower but more even flow at one end of the tank, but at the moment everything is actually doing fine in the tank, so think I should relax and enjoy for a while


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