RO Filters

[Mash Monster]

Based on your post I bought one of these and used it yesterday, it made a big difference. Thank you.

Without the pump I get just 4 litres per hour, with it I get 14. Yesterday I collected 24 litres in well under 2 hours rather than 6.

Glad it’s helped you out I couldn’t believe the difference and had to check I’d plumbed it in correctly a great improvement and time saver too

 

[The-Engineer-That-Brews]

Based on your post I bought one of these and used it yesterday, it made a big difference. Thank you.

Without the pump I get just 4 litres per hour, with it I get 14. Yesterday I collected 24 litres in well under 2 hours rather than 6.

Did you have to make any change to the flow restrictor for the 'bypass' (black) water with that?

 

[Hazelwood Brewery]

Did you have to make any change to the flow restrictor for the 'bypass' (black) water with that?

No, the pump has been designed to pair with the 50GPD system. They also sell other pump models matched to other RO models such as their 150GPD system.

 

[Benfleet Brewery]

Based on your post I bought one of these and used it yesterday, it made a big difference. Thank you.

Without the pump I get just 4 litres per hour, with it I get 14. Yesterday I collected 24 litres in well under 2 hours rather than 6.

Did you experience a similar reduction in the waste water too? I’m not too fussed about the time it takes for me to draw off the RO water but I would quite like to reduce the wastage.

 

[Hazelwood Brewery]

Did you experience a similar reduction in the waste water too? I’m not too fussed about the time it takes for me to draw off the RO water but I would quite like to reduce the wastage.

I’ve not measured that as yet but will report back when I do.

 

[The-Engineer-That-Brews]

My understanding is that, regardless of the pressure, the ratio of 'waste' to filtered water needs to be about 4:1 so that the membrane is properly flushed during use - otherwise its lifetime will be adversely affected

 

[chrisb8]

Surely the volume of waste water will be exactly the same per volume of ro water produced, just wasted quicker?

 

[Hazelwood Brewery]

Surely the volume of waste water will be exactly the same per volume of ro water produced, just wasted quicker?

I’ll let you know later. I guess in theory a lower pressure could mean less water is pushed through the membrane and instead just flows past it. At higher pressure, because outward flow is restricted, more might pass through the membrane.

 

[The-Engineer-That-Brews]

Surely the volume of waste water will be exactly the same per volume of ro water produced, just wasted quicker?

Yes in fact you want this to be the case (about 4:1 ratio) in order to preserve the life of the membrane.

The internal 'plumbing' of these systems is really simple:

The 'waste' water isn't really dirty or anything, it's just got a slightly higher (about 25%) concentration of ions that can't get through the membrane.
The reason you need a decent waste flow rate is to keep the mineral concentration on the 'input' side of the membrane down to a sensible level so it doesn't overload the membrane :-)

 

[Hazelwood Brewery]

The results are in…

No pump, 525ml RO, 1900ml waste

Pumped, 500ml RO, 1100ml waste

 

[The-Engineer-That-Brews]

Sounds to me like you might need to increase the bypass flow rate a bit when you're using the pump...

From Residential RO Systems -waste to pure ware ratio explained - Pacific Water Technology :

"Discerning buyers who are in the market for a new reverse osmosis system look at a number of factors to ensure they get value for money. One of the more common question asked is; what is the waste to pure water ratio on your Reverse Osmosis Units? The answer I have is be very careful when a water filter company tells you they have a 1:1 ratio and we see this a lot:​

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“NEW AND IMPROVED LOWEST WASTE TO PURE WATER RATIO ON THE MARKET 1:1”​

​

The truth is that residential RO systems have a waste: pure water ratio that is set by the membrane supplier. The ‘waste’ water is required to flush the membrane and ensures that you can achieve a reasonable life span of 2-3 years before having to replace the membrane. Any low ratio like 1:1 will ensure that the membrane needs to be replaced well before the typical life expectancy –ironically a bonus for the unscrupulous salesman who promised you the outrageous ratio.​

​

Residential RO systems have a waste: pure water ratio of 3 to 5 to 1 (average 4:1) and the actual ratio should depend on a number of factors including water quality ,pH, pressure and temperature. In reality this ratio is set and predetermined, thanks to a flow restrictor that is sized according to the membrane output."​

 

[chrisb8]

The results are in…

No pump, 525ml RO, 1900ml waste
View attachment 52146

Pumped, 500ml RO, 1100ml waste
View attachment 52147

I stand corrected but I'm still not sure how

 

[The-Engineer-That-Brews]

I've now also realised that when I switch to my higher capacity (150 GPD) replacement membrane, I also need to change the flow restrictor...

 

[The-Engineer-That-Brews]

I stand corrected but I'm still not sure how

You mean why the ratio has changed just by using the pump?
I think that's just because the flow restrictors in these systems are nothing special, so with double the pressure their flow rate does not double; whereas the membrane has a large surface area, so its ratio of flow rate to pressure is more linear.

 

[Hazelwood Brewery]

I stand corrected but I'm still not sure how

The water will take the path of least resistance. At low pressure that’s the restricted flow path, at high pressure it’s the membrane.

An analogy - two exits from a building, a revolving door (the membrane) and a open door next to it. People will tend to use the open door while it’s free flowing but as more people try to leave the building the open door starts to get a bit congested and people will instead start to use the revolving door. You may still get 200 people through but the faster those 200 leave, more will opt to use the revolving door.

 

[chrisb8]

You mean why the ratio has changed just by using the pump?
I think that's just because the flow restrictors in these systems are nothing special, so with double the pressure their flow rate does not double; whereas the membrane has a large surface area, so its ratio of flow rate to pressure is more linear.

The water will take the path of least resistance. At low pressure that’s the restricted flow path, at high pressure it’s the membrane.

An analogy - two exits from a building, a revolving door (the membrane) and a open door next to it. People will tend to use the open door while it’s free flowing but as more people try to leave the building the open door starts to get a bit congested and people will instead start to use the revolving door. You may still get 200 people through but the faster those 200 leave, more will opt to use the revolving door.

So I suppose the important question is whether the two samples are the same in terms of the tds....?

 

[Hazelwood Brewery]

So I suppose the important question is whether the two samples are the same in terms of the tds....?

I did check that

The RO water from both was 0. The waste (unpumped) was 388, waste (pumped) was 412.

 

[The-Engineer-That-Brews]

The waste (unpumped) was 388, waste (pumped) was 412.

Yep that sounds about what you'd expect isn't it. So to get the same life out of your membrane you'd have to increase the waste flow rate until the TDS was back down to 388... Anyhow, the water isn't really 'waste' - it's just got a bit higher mineral content so it's fine to use on the garden, for washing up etc :-)

 

[The-Engineer-That-Brews]

Actually I wonder if a good use for 'waste' water would be to pump it through your counterflow to aid cooling

 

[Hazelwood Brewery]

Actually I wonder if a good use for 'waste' water would be to pump it through your counterflow to aid cooling

You could do that to heat it before you use it to wash up, then use it to water the garden.