RO continuously flowing to drain

[sm30]

My RO system just started continuously flowing to the drain. I have been reading it could be the automatic shutoff valve or the check valve. I shutoff the tank valve and waited 5 minutes however the water did not stop flowing to the drain. The second test I did was shut off the main water valve to the RO and the water did stop flowing to the drain (tank valve was open for this test).

I am assuming the automatic shutoff valve needs replacing, but I have a couple of questions.

1) Do you recommend I also replace the check valve?
2) The system is only 3 years old, is it normal for this part to fail this early?

 

[Bannerman]

The ASV (aka: ASO) is a fairly simple device that will shut off RO water production once the storage tank pressure has risen to 60% of the supply pressure.

Depending on which model ASV your system is equipped with, you maybe able to restore operation by disassembling the ASV, rinse off the internal components with fresh water and then reassemble.

 

[Sponsor]

 

[sm30]

If the pressure in the storage tank is low, would this also cause water to continuously flow to the drain?

 

[Bannerman]

By the pressure in the storage tank being low, do you mean the pre-charge air pressure as measured when the tank contains no water?

When the air pre-charge pressure is insufficient, the storage tank will store a greater volume of water, but with a low volume of air to push that water out from the tank, the pressure to the faucet will rapidly fall, even when a relatively small quantity of RO is drawn.

To optimize storage capacity while providing sufficient pressure to push water out from the tank to the RO faucet at a reasonable rate even while there is little water remaining in the tank, the storage tank pre-charge pressure is normally adjusted to 7 psi.

Regardless of whether the air pre-charge is 3, 7 or 10 psi, while RO water is being produced and is filling the tank, the pre-charge air will further compress which will cause the storage/system pressure to rise.

When using a standard ASV, once the system pressure has risen to 60% of the incoming supply pressure, the ASV will then stop production by shutting off all incoming flow to the RO membrane which will also stop drain flow. For example, if your incoming municipal supply pressure is 60 psi, then the ASV will continue to allow production and drain flow until the system pressure has risen to 36 psi.

Until the system pressure has risen to 60% of the supply pressure, production will continue and water will continue to flow constantly to drain.

 

[sm30]

Yes, I meant the air pressure in the tank when it's empty. When my tank was empty I was not getting a reading on my pressure gauge. So I added air until the gauge showed 7 psi.

So in other words regardless of the tank pressure being low, normal or high, the ASV will reach 60% at some point, correct?

I am just trying to rule out if my tank being low in pressure would also cause water to continue to flow constantly to the drain. Now that my tank has 7 psi I am letting the RO system run for 1-2 hours to see if it will shut off.

I am assuming if at this point it does not stop drain flow, then the ASV needs replacing?

 

[sm30]

Update to my last post:

I let the RO system run until the tank was filled and monitored the water usage over night. Over 9 hours there was a slow trickle to the drain that amounted to 20 litres.

By adding more pressure to the tank it reduced the amount of water that is flowing constantly to the drain. So does this mean just the ASV needs replacing? Or something else as well?

 

[sm30]

Anyone have any thoughts?