# Physics question



## Jack B (8 Aug 2021)

Hi all

I know water flows slower through a narrow pipe...but does it help if most of the pipe is a large diameter? I'm stuck with a relatively narrow inlet to the tank from my sump, but if I increase the diameter of the pipe leading to it (and connect it to the inlet via a pipe reducer) will that significantly help the flow rate?

I ask because I'm about to fit a non-return valve and want to mitigate the associated reduction in flow, if I can.


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## foxfish (8 Aug 2021)

What sizes are you talking about and what sort of return pump ?
Depending on design and position, non return valves can really restrict flow!
I have always strived to avoid non return valves.


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## Zeus. (8 Aug 2021)

*Flow rate varies inversely to length*, so if you double the length of the pipe while keeping the diameter constant, you'll get roughly half as much water through it per unit of time at constant pressure and temperature.

So the shorter the constriction the better. Although once you reduce the flow the pump will create a higher pressure in the pipe, so the increase pressure will increase the flow but not as much as not having the constriction. I try and keep all constrictions/bottlenecks as short as possible to decrease resistance and optimise output.

I'm with @foxfish, avoid non return valves as they will reduce flow esp with water compared to CO2


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## Ehcosbie (8 Aug 2021)

Continuity equation
Bernoulli’s equation/principles
Venturimeter


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## tiger15 (8 Aug 2021)

foxfish said:


> What sizes are you talking about and what sort of return pump ?
> Depending on design and position, non return valves can really restrict flow!
> I have always strived to avoid non return valves.


The flow rate depends on the size of your pump, and the frictional losses the flow has to encounter.  To maximize the flow, you have to minimize friction which is proportional to the length of the pipe, number of fittings (elbow, valve, reducer), and inversely proportional to the diameter of the pipe.   Pipe fittings induce huge losses, so it is best if you can avoid installing the non return valve.  Increasing the size of the pipe will increase flow, but since you cannot eliminate the reducer, the flow increase will not be substantial. The simplest way to increase flow rate is to increase the pump size  but at the expense of greater inefficiency and energy input. 

What is your objective of increasing the flow rate, to increase filtration or circulation?  A sump system doesn't require the highest flow rate to be efficient as it has the largest, most efficient filter media.  If increasing circulation is your objective, it is easier  to accomplish by installing in tank circulation pump.


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## Jack B (8 Aug 2021)

Thanks for the help!

The problem I'm trying to fix is that if I get a powercut, water is drawn back through the tank inlet, down to the return pump. All of my fish are small enough to be sucked in, especially my expensively-assembled shoal of chilli rasboras. If I can solve this without using a non-return valve then great. 

Here's a quick video of the current setup

And some pics:





















(The ugly blue tubing is my latest attempt to revive some stubbornly unhappy Frogbit)

The pump is an Octo Varios 2, with a 1" outlet connected to a short section of 1 1/4" OD, stiff PVC pipe. That's connected to the tank via a 1" OD 3/4" ID flexible pipe (not sure what plastic - it's more stiff that the clear waterchange-style pipe). The 90degree elbow into the tank is OD 3/4". 

I currently have to run the pump at full rate to get the flow I'm after (enough for the bamboo shrimp to seem happy). If I see an Octo Varios 4 on Ebay I'll snap it up and sell my current pump.

I already own a non-return valve: one of these, which I saw recommended in another thread. it does seem to be well engineered, but I've not tested it. 

I'm poised to visit B&Q with my non-return valve, pump and tubing to see if I can cobble together a system, but would far rather get advice from those in the know! All ideas gratefully received


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## Nick potts (8 Aug 2021)

Can you not add a grill, duckbill or similar outlet to the flow side? What brand tank is it (It looks similar to a TMC signature)

I would also get a proper inlet grill on the overflow side as well, the sponge and plants are liable to block and cause an overflow. What is the green intake for, are you running another filter?


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## sparkyweasel (8 Aug 2021)

Could you put mesh or sponge on the inlet to keep the fish safe?


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## sparkyweasel (8 Aug 2021)

Oops, slow typing.


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## Wookii (8 Aug 2021)

Agree with @Nick potts - add some mesh over the sump return inlet in the tank. I’ve used loads of this mesh off eBay for various things in tank - it shouldn’t restrict the flow too much, but will prevent Chilli’s getting through:









						1m x 0.8m PLASTIC NET STRONG BLACK FLEXIBLE HDPE INSECT FISH MESH SCREEN FINE2mm  | eBay
					

Find many great new & used options and get the best deals for 1m x 0.8m PLASTIC NET STRONG BLACK FLEXIBLE HDPE INSECT FISH MESH SCREEN FINE2mm at the best online prices at eBay! Free delivery for many products.



					www.ebay.co.uk


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## Jack B (8 Aug 2021)

Thanks everyone, this is very helpful 



Wookii said:


> Agree with @Nick potts - add some mesh over the sump return inlet in the tank. I’ve used loads of this mesh off eBay for various things in tank - it shouldn’t restrict the flow too much, but will prevent Chilli’s getting through:
> 
> 
> 
> ...


Good stuff, thanks all. This link looks useful...


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## Jack B (8 Aug 2021)

Nick potts said:


> Can you not add a grill, duckbill or similar outlet to the flow side? What brand tank is it (It looks similar to a TMC signature)
> 
> I would also get a proper inlet grill on the overflow side as well, the sponge and plants are liable to block and cause an overflow. What is the green intake for, are you running another filter?


Yes it's a TMC signature that I got second hand. I do have what I assume you mean by a duckbill, which increase the speed of the water entering the tank a bit too much. I could turn down the pump obvs but I was always nervous of falling short of the required filtration rate; my tank has upwards of 70 nano fish which is guess is pretty heavy stocking. And I'd still need a grill on the duckbill? 

A circulation pump is an interesting idea. I've always baulked at the look of them but maybe it'd look OK directly under the inlet

When you say a proper grill do you mean Wookii's mesh? 

The second outlet is just to increase the rate of outflow to the point that the clogging you refer to doesnt create an issue. Not exactly super elegant tho


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## Jack B (8 Aug 2021)

Oh I remember: I used the foam cover on the outlet to stop RCS shrimplets getting sucked through. Forgot to mention them


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## Jack B (11 Jan 2022)

Wookii said:


> Agree with @Nick potts - add some mesh over the sump return inlet in the tank. I’ve used loads of this mesh off eBay for various things in tank - it shouldn’t restrict the flow too much, but will prevent Chilli’s getting through:
> 
> 
> 
> ...


Finally got round to buying some of this: really chuffed with how little it restricted the flow. Thanks @Wookii


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## dw1305 (12 Jan 2022)

Hi all,
I can't help with the physics, but @Jack B have you changed your fertiliser recently?





In the photo it looks like the Frogbit (_Limnobium laevigatum_) has been iron (Fe) deficient (the <"reticulated patterns"> on the older leaves), but <"it is now recovering">. The other option would be <"magnesium (Mg) deficiency">, this is more likely if the younger leaves have always been green, but the older leave have always yellowed and senesced farly quickly?

Have a look at <"Frogbit taken a turn">.

cheers Darrel


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## Jack B (13 Jan 2022)

dw1305 said:


> Hi all,
> I can't help with the physics, but @Jack B have you changed your fertiliser recently?
> 
> 
> ...


Thanks Darrel,

Ah yes - this is an old photo now! In fact you and @AverageWhiteBloke kindly pitched in already. The ultimate solution remains something of a mystery, though anchoring the frogbit / reducing the flow did help. The problem was eventually bypassed by the introduction of some rather vigorous dwarf water lettuce that has completely taken over...


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