RODI System Electrics - how does this work?

[jesteh]

Trying to build my own RODI system and really struggling to understand electric setup. I am enclosing diagram from one of the pre-built systems - I looked at the different ones and they are all wired the similar way.
Key aspect is that power supply is connected through the pressure switch.
As I understand it, the pressure switch detects pressure change (e.g. empty tank) and closes the circuit energising pump, solenoid valve, etc.
This starts pushing the water through the RO membrane until tank is full. Pressure switch detects tank full and opens circuit - everything turns off.
So the pressure switch controls the circuit through a pressure change detection.
But what I don't understand is the Auto Flush - this is meant to turn on periodically and flush the membrane. It is however only energised when pressure switch closes the circuit. So how can it fulfil its function - its never normally energised and therefore can't periodically flush the system?!?
What am I misunderstanding?

 

[gbroadbridge]

Trying to build my own RODI system and really struggling to understand electric setup. I am enclosing diagram from one of the pre-built systems - I looked at the different ones and they are all wired the similar way.
Key aspect is that power supply is connected through the pressure switch.
As I understand it, the pressure switch detects pressure change (e.g. empty tank) and closes the circuit energising pump, solenoid valve, etc.
This starts pushing the water through the RO membrane until tank is full. Pressure switch detects tank full and opens circuit - everything turns off.
So the pressure switch controls the circuit through a pressure change detection.
But what I don't understand is the Auto Flush - this is meant to turn on periodically and flush the membrane. It is however only energised when pressure switch closes the circuit. So how can it fulfil its function - its never normally energised and therefore can't periodically flush the system?!?
What am I misunderstanding?

I don't understand the diagram, however you normally flush the membrane at the point when you first start a RODI system.

The purpose is to flush out any high TDS water sitting on the inlet of the membrane until the presure builds up sufficiently for the membrane to work.

Without flushing, the membrane will pass high TDS water through, which will cause rapid exhaustion of the Doionisation resin. People call it TDS creep.

So the flush solenoid needs to operate (be energised) until pressure builds up enough to open up the pressure switch (which turns it off).

 

[Joe31415]

I can't speak specifically to your pump, but generally the auto-flush only happens when the system is actively running.

ETA, deleted what I wrote earlier. I'd rather see the directions for myself rather than speculate. However, it should be noted that the pressure switch, by itself, won't sense that the bucket is full. It only reacts to pressure building up in the system due to the RODI outlet be closed. Generally, due to a float switch.

 

[Biglew11]

The pressure switch is open when there it high pressure tank full. and closed when there is low pressure, tank empty.

The auto flush valve is energized when the pressure switch is closed, filling whatever you're putting rodi into when the bin is full the pressure switch detects the high pressure opening the circuit.

 

[jesteh]

I misunderstood what the auto flush actually does. I understood that it periodically runs the water through the membrane while NOT in use.
I understand now that it only operates while the membrane is in use by opening and closing the restriction - is that correct?

 

[gbroadbridge]

OK, I think I misunderstand what the auto flush actually does. Can anyone explain it to me?

I did in post #2

 

[gbroadbridge]

I misunderstood what the auto flush actually does. I understood that it periodically runs the water through the membrane while NOT in use.
I understand now that it only operates while the membrane is in use by opening and closing the restriction - is that correct?

Yes, it has nothing to do with detecting when a container is full.

If I understand the wiring diagram correctly ...

The pressure switch should be normally closed and on the input to the membrane (after the carbon filter).
It will energise the bypass solenoid until the pressure builds up from the pump. The bypass solenoid valve whould be connected from the output of the membrane to waste.

Hopefully I got that right. lol.

edit: Do a search on TDS creep

 

[Biglew11]

Yes, it has nothing to do with detecting when a container is full.

If I understand the wiring diagram correctly ...

The pressure switch should be normally closed and on the input to the membrane (after the carbon filter).
It will energise the bypass solenoid until the pressure builds up from the pump. The bypass solenoid valve whould be connected from the output of the membrane to waste.

Hopefully I got that right. lol.

edit: Do a search on TDS creep

Think you're confusing auto flush with bypass valve. 2 different things.

Here auto flush takes the place of the flow restrictor and removes build up from the high pressure side of the membrane.
The solenoid and auto flush is energized the entire time the system is runing and is located at the input of the whole system. It takes the place of an auto shut off valve. The high pressure switch is located between the ro and the di.and between the ro and the high pressure switch should also be a check valve that holds the high pressure on the switch when the solenoid closes and the ro looses pressure.

The auto flush when energized has an internal timer that bypasses the flow restrictor completely, for about 15 seconds about once an hour.

No reason to flush the product line at regular intervals like this.

 

[jesteh]

Ok, that makes sense completely now - thank you so much for such quick and comprehensive answers.
One further question , most of the systems appear to have auto flush solenoid on concentrate side. I noticed one of the diagrams has auto flush solenoid on both concentrate and permeate.
Can I check what would purpose of auto flush be on permeate side? Diagram I noticed this on is included below

 

[Biglew11]

Thats the first time I've seen a diagram with flush valve on the permeate line, but that should be straight through and only needs to activate at start up.

That valve would flush the high tds water at startup, tds creep. When the system shuts down when full, the tds on the permeate side creeps up to about the same level as the water coming into the system. This high tds water at start up wastes your di resin.
Its really more important to flush this than it is the waste side of the membrane.