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Reducing flow - intake or outflow?

Luvlyjub

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18 Feb 2021
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46
Location
Essex
With some external filters there is an option at point of tank entry to adjust the flow of both in/out pipe connections.

If I want to reduce my flow what one do I adjust - or does it not matter?

Or should you adjust both evenly?

Cheers
 

bazz

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24 Jan 2009
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Lincoln
Hi,
Most filters that have built in flow adjustment usually throttle the outflow (as on my 2081), and this is option I use on my Oase Filtosmart 200 which has adjustment on both.
I've noticed a few filters have a larger inflow diameter pipe than the outflow leading me to think that you should not really be obstructing the inflow.
Hope this makes sense,
Cheers!
 

Luvlyjub

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18 Feb 2021
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Essex
Interesting as it is the Oase 200 Filtosmart I am using as a second filter with the spay bar as wanted to lower flow for this with surface movement. I was not sure if you over restricted flow using both in and out adjustment it could affect motor? As you have this adjustment on both connectors you would have thought there may be better instruction in the manuals.

I will leave the adjustment to the outflow as suggested and may send an email to Oase for comment.
 

bazz

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24 Jan 2009
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Yes, it appears that that they are a universal part used for both in and out. Surprising really as some of the larger Oase filters notoriously suck in air and stifling the intake is only going to exacerbate the problem.
All extras, inline diffuser inline heater etc, should be installed on the outflow, although a lot of people use prefilters without any problems.
 

Luvlyjub

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I do find the Filtosmart very noisy and in some way wish I purchased the 100 model as flow would have been fine with that. But it seemed a no brainer to spend an extra £15 as the 100 has a 1.3L volume and the 200 4.2L. You can never have enough filter volume but I suppose you can have too much flow.
 

ian_m

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If using a valve to reduce filter flow, generally and flow reducing valve should be on the output.

If reducing flow on the input the pumps impellor can cavitate and/or pull air out of the water, end up making a noise, making the filter "burp" air, reducing the cooling water flow around the impellor magnetic and reducing the lubrication effects of the water.

Also if reducing the outflow, most filter instructions I have seen state "do not reduce flow to greater than half in order to preserve the life of the pump".
 

lazybones51

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18 May 2017
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If using a valve to reduce filter flow, generally and flow reducing valve should be on the output.

If reducing flow on the input the pumps impellor can cavitate and/or pull air out of the water, end up making a noise, making the filter "burp" air, reducing the cooling water flow around the impellor magnetic and reducing the lubrication effects of the water.

Also if reducing the outflow, most filter instructions I have seen state "do not reduce flow to greater than half in order to preserve the life of the pump".
On the filters I have seen or owned, the pump is after the filtration media. So as the filtration media gets dirty/clogged, it will restrict the flow of water to the input side of the pump. So in theory the pump must be able to safely handle a certain amount of restriction on the input side before it becomes an issue?
 

zozo

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16 Apr 2015
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The pumps we use are all AC (Conduction) motors... :) You also could consider a Variac (Variable AC controller) to regulate its RPM. In the old days, Variacs used to be rather bulky actually still available today in the same fashion for bigger motors such as air conditioner fans or ceiling fans etc.
metered-variac-variabler-ac-ausgangswandler-2-ampere-0-250v-tdgc2-0-5kva-power-transformers-6276-700x700.jpg


But nowadays they also exist in electronic mini versions as AC motor controllers via eBay and Amazon for a few bucks. If the description states it's an AC dimmer it should say it's suitable for fans, then you're good to go. Don't use single-phase light dimmers they will make the motor make a humming sound. :) Best is to search for AC Motor Speed Controller, that's different from dimming.

Or switch to a prefilter setup and hook a DC pump to it and find a PWM motor controller, this also works a charm... I ran it for over 6 years without any issues at various speeds and in several experiments.

Always better to play with motor speed than run it full speed and reduce the flow through.
 

Luvlyjub

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That would make sense if they could be standard fit to control motor speed.

I believe I saw a video that Green Aqua were testing a Beta electronic flow controller unit hooked up to outflow that you could pre-set level and it would monitor performance against target.
 

tiger15

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14 Mar 2018
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Most filters come in model series, and smaller model has smaller impeller. If you can find a smaller impeller to fit, it can reduce flow smoothly without back pressure and compromise of pump longevity.

I use only HOBs and don’t know if it can be done with canister filters. I replaced all my HOBs existing impeller with smaller impeller of the next smaller model.

Customers rate filters by their flow rate, more is perceived better. HOBs have a bottleneck effect of having over sized pump and under sized media volume. So I find it beneficial to reduce flow by replacement with a smaller impeller. It makes less noise. It promotes slower but more thorough clogging of the media, thereby reducing media cleaning frequency while increasing mechanical filtration effectiveness.
 

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