RO/DI needs check valve before auto shutoff?

[wwu123]

Just a question on plumbing my auto-shutoff for my RO/DI. I've had the ASO pre-installed on my BRS unit for over a year, but never really used it since I made water in batches. Now I've moved my RO/DI to the basement and have a float switch on a Brute trash can.

The float switch and ASO seem to slow the RO/DI production to a halt, as well as any water running through the waste line. However, I came back a few days later to find that the trash can had overflowed and the float valve was completely submerged.

I noticed on some Spectrapure diagrams posted here that they suggest a check valve before the ASO (but after the RO membrane). I think the comment was that this would ensure sufficient pressure on the ASO to force the shutoff. BRS does not pre-install a check valve here, nor do their instructions suggest one.

1. Is the lack of a check valve here causing incomplete shutoff, leading to a slow overflow?

2. Is my drinking water RO splitoff perhaps contributing to the problem? Probably 10 times a day we dispense a few cups of water from the kitchen sink. Each time it causes some modest product of RO through the membrane, is it forcing flow through the DI each time? BTW there is a check valve on this line, but it is after the split tee for the DI.

3. Or is my float switch perhaps faulty? How should I test it here? The switch slows down the flow, but without the ASO it cannot shut off 62 psi by itself, so it is not a watertight switch.

 

[pweissma]

You need the check valve for the auto shut off to work.

 

[bertoni]

I can't help with this one. I can move this thread to the equipment forum, if you'd like.

 

[pweissma]

The check valve is absolutely necessary. Without it you will get the behavior you describe. This happens because the water flows back through RO membrane which prevents pressurization of the line between the RO membrane and the float valve. Without pressure in this line the ASO won't activate and shut off flow into the the RO membrane.
You should have a constant trickle of brine to your drain. I would think that the float valve should prevent RO water from overfilling your reservoir. There may be a problem with you float valve but get a check valve first.

 

[kgross]

Yes the check valve is required. but I think you also have a failure in your float valve. The check valve will allow the ASO to turn back on, and allow water to go to waste, but the float valve should not allow anything to make it into the tank.

 

[wwu123]

Thanks, I'm checking with BRS on what they advise as well. Basically the BRS layout has a check valve, it is after the RO membrane, after the ASO, after the tee for the RO vs DI. The Spectrapure diagram has it after the RO membrane, before the ASO, before the tee.

So should I just move it?

 

[kgross]

Like I said, the check valve is needed for the aso to work correectly, but your problem is your float valve is leaking. Doesn't matter if the aso works correctly or not, if the float valve is leaking. On moving the check valve, it will depend on the aso valve. It sounds like BRS has an aso valve that does not matter where the check valve is, I don't think BRS would sell it setup so the aso would not stay shut off.

You said the water going to the drain stopped, which is what the ASO is for, it is the float that stops the water going into the trash can. Your float is defective or has something in it, allowing a slight leak.

 

[pweissma]

Thanks, I'm checking with BRS on what they advise as well. Basically the BRS layout has a check valve, it is after the RO membrane, after the ASO, after the tee for the RO vs DI. The Spectrapure diagram has it after the RO membrane, before the ASO, before the tee.

So should I just move it?

An ASO is a simple device. It requires pressure in the permeate line (the good clean RO water) to close and thereby turn off the flow into the RO membrane. This pressure is created between the closed float switch and check valve (assuming the check valve is where it should be per the Spectrapure diagram).

Without the check valve a pulsing will happen. The pressure will build between the RO membrane and the float switch. The ASO will close and the pressure is relieved from the input side of the RO membrane as it should. But then the lack of pressure going into the RO membrane will translate to a lack of pressure in the permeate line. This will allow RO water to flow back into the RO membrane. When this happens the ASO opens again and the cycle repeats.

 

[wwu123]

Like I said, the check valve is needed for the aso to work correectly, but your problem is your float valve is leaking. Doesn't matter if the aso works correctly or not, if the float valve is leaking. On moving the check valve, it will depend on the aso valve. It sounds like BRS has an aso valve that does not matter where the check valve is, I don't think BRS would sell it setup so the aso would not stay shut off.

You said the water going to the drain stopped, which is what the ASO is for, it is the float that stops the water going into the trash can. Your float is defective or has something in it, allowing a slight leak.

Thanks, I believe you are exactly right here.

First, to correct any misconceptions about the BRS setup, their customer service let me know there is actually a check valve before the ASO - it's in an elbow coming out of the RO membrane, so it wasn't immediately obvious. So wasn't any need to relocate the other check valve.

With the check valve in place, BRS also honed in on the float valve being the problem. I had suspected it could be faulty, but it's hard to see because the leak seems nearly imperceptible. But both you and BRS have pointed out that a properly working float valve should have been able to prevent the water level from further rising, which it failed to do.

 

[bertoni]

Without the check valve a pulsing will happen. The pressure will build between the RO membrane and the float switch.

Interesting. Thanks for posting that!