RODI modification. Good or bad?

[Chompers]

I disagree. Sediment filters will offer little to no pressure drop, unless you pack them tightly. In other words, pressure will equal out on both sides of the sediment filter, because your biggest restriction is at the membrane. You can bottleneck anything, and pressure will equalize, but once you pass your largest restriction, pressure will drop. If your sediment filter is your largest restriction, something's wrong.

It took a while to sink in, but I see what you are saying. That's pretty interesting and it makes sense. I think I might add some pressure gauges during my next upgrade. Two of my canisters are not see through and one had a sediment filter that was pretty bad at a past change. Since then I have added a clear sediment filter ahead of everything and have been considering maybe a second in parallel with the first.

 

[Ron Reefman]

I disagree. Sediment filters will offer little to no pressure drop, unless you pack them tightly. In other words, pressure will equal out on both sides of the sediment filter, because your biggest restriction is at the membrane. You can bottleneck anything, and pressure will equalize, but once you pass your largest restriction, pressure will drop. If your sediment filter is your largest restriction, something's wrong.

You are absolutely right!

And what the OP has designed isn't all that different than the Spectrpure design that AZDessertRat posted. Spectrapure has 1 extra downstream RO membrane and the OP has 3 with a booster pump in front of them. I'm not sure, but I don't think, the first RO membrane can supply enough water to support the booster pump and 3 additional membranes.

I collect my reject water in a 240g cistern (I make a lot of water for 4 tanks) and use it for doing laundry. My wife doesn't mind because doing the laundry is one of the household jobs I assume responsibility for! BWT, my 3600gph pump on the cistern fills the washing machine faster than the washing machine can!

 

[AZDesertRat]

Sounds good in theory but that is not correct. Place two pressure gauges on the incoming water supply, one before the sediment filter and one after the carbon block or on the membrane housing as many systems come with. You will notice a slight pressure drop or headloss when the system is flowing if you are using high quality filters meaning they are doing their job or protecting the membrane down to near micron levels. A 75 GPD system flows about 1 quart a minute so even though the membrane is the biggest bottleneck there is still headloss in the rest of the array. Start stacking membranes on and the 10" filters soon have too much headloss for the membranes and you need to switch to 20" filters or parallel filters to keep up efficiently.

 

[Engloid]

Sounds good in theory but that is not correct. Place two pressure gauges on the incoming water supply, one before the sediment filter and one after the carbon block or on the membrane housing as many systems come with. You will notice a slight pressure drop or headloss when the system is flowing if you are using high quality filters meaning they are doing their job or protecting the membrane down to near micron levels. A 75 GPD system flows about 1 quart a minute so even though the membrane is the biggest bottleneck there is still headloss in the rest of the array. Start stacking membranes on and the 10" filters soon have too much headloss for the membranes and you need to switch to 20" filters or parallel filters to keep up efficiently.

To achieve pressure, you first have to have flow. If you are past your largest restriction, your pressure may reduce, but you will still have the same flow rate. Before that largest restriction, you will have higher pressure. Just think of a garden hose. Kink it a little...and it will slow flow and increase pressure before the kink. Now put your thumb over half of it like you would to spray it. You will have same flow rate, but you may now equalize pressure before and after the kink.

In theory, both your pressure gauges would show the same pressure, if put in the same place. In reality, these pressure gauges are not calibrated gauges. I've had many experiences with NIST traceable calibrated gauges that will not read the same right next to each other. There are factors such as accuracy percentage also. If a gauge says it's calibrated and accurate within 2% and is a 600psi gauge, that means it's accurate within 12psi. It isn't relative to the pressure read, it's relative to the max pressure of the gauge. I spoke to Ashcroft, one of the leading industrial gauge manufacturers just a week or so ago about this, in regards to testing of pressure vessels at work.

 

[joeyhatch11]

I do the same, right into the washer. No water loss, not wasting more water later doing laundry. I have low TDS and not so hard water so I run a 2:1 Spectrapure 90GPD set up, with booster pump. System has been up and running for about 8 months now. All filters are still looking amazing and DI hasn't changed color yet either. I have 1-2 TDS coming out of the membrane, sometimes 0. And always 0 coming out of DI of course.

 

[azjohnny]

If you are on a sewer you are not wasting water by putting it down the drain, the water makes its way back to the sewage plant where it will be processed into usable water. It will cost you about $5 a month on your water bill to make water for WCs and top off

 

[AZDesertRat]

There is a headloss across the sediment and carbon filters no matter what you think. Again place two traceable 100 psi pressure gauges on the incoming and after the carbon filters. With good low micron absolute or near absolute filters you will see a difference which will grow as the filters become seasoned and when they start fouling. You are quoting theory not a practical application.
If you are using coarse filters they may not be any headloss but then again you might as well have a piece of window screen as a filters for all the good they are doing at protecting the pores in the carbon block and the RO membrane.

 

[Ron Reefman]

There is a headloss across the sediment and carbon filters no matter what you think. Again place two traceable 100 psi pressure gauges on the incoming and after the carbon filters. With good low micron absolute or near absolute filters you will see a difference which will grow as the filters become seasoned and when they start fouling. You are quoting theory not a practical application.
If you are using coarse filters they may not be any headloss but then again you might as well have a piece of window screen as a filters for all the good they are doing at protecting the pores in the carbon block and the RO membrane.

So it sounds like you have already done this experiment? And what was the pressure before and after?

 

[AZDesertRat]

There is no "one" answer, there are so many variables including input pressure, micron rating, porosity or absorbency of the filters, size and efficiency of the RO membrane, water temperature which affects viscosity etc.
A 1-2 psi drop when the filters are new is not uncommon though.

 

[Ron Reefman]

So you are warning about a 2-5% pressure loss. OK. I'll move on.

 

[AZDesertRat]

It doesn't sound like much but that is with new filters. As little as a 2% drop in rejection rate or membrane removal efficiency cuts your DI resin life in half meaning you spend twice as much annually on replacement DI. A RO/DI is a complete system from the sediment filter to the permeate line and everything in between needs to be thought out correctly or it affects everything downstream of that point and ends up costing you more money.

You reduce the pressure available to th membrane you reduce its efficiency. You reduce its efficiency you raise your RO only TDS and shorten the DI life. It all makes a difference no matter how small or insignificant it seems on the surface.

 

[Aaron_B]

Hello, I'm also thinking of implementing a RO/DI System and already have a Water Softner

 

[Aaron_B]

Sorry, That's I already have a Water Softener and was wondering if I should place the RO/DI Unit downstream of the Softener or before it? And does it matter what type of salt that I'm using to "soften" the water with? (Am using potassium chloride - I believe.) Thanks, Aaron

 

[AZDesertRat]

Always use softened water for your RO or RO/DI system when possible. All membrane manufacturers recommend soft water and most will not hono a warranty claim if youdo not use soft water.
It does not matter if it is sodium or potassium, both are like pretreatment for the RO membrane so it does not have to work as hard, gives you lower TDS and lasts much longer.