Auto shut off valve in inlet or waste of membrane?

rajdude · Jun 9, 2022

Hello everyone
About the Auto Shut off valve in a RO water filter system... I see two ways of installing it.
The most common way of installing it is so that the ASOV shuts off water flow coming into the membrane.
I have also seen another way, where the ASOV shuts off drain water (coming out from the membrane).

Some people say the second one is the correct one and others say that no, the first one is correct.

I have seen both connection diagrams work fine. Is there any advantage of using one over another?

Thanks
-Raj

Reference:

First way:

Installing an Auto Shut Off Valve

Auto shut off valves use a small amount of pressure created by your float valve to shut off the water supply to your RO membrane. Follow these instructions to install an auto shut off valve on your RO system. First note the top and bottom of the shut off valve, the bottom has screws and the

www.bulkreefsupply.com

105111-Auto shut off valve for Reverse osmosis Water System

www.maxwaterflow.com

Second way:

This is the alternative one, which some people on another reefing forums swear by.

Biglew11 · Jun 9, 2022

Both set ups will work. But putting the a.s.o. in the waste line keeps the filter canisters at house pressure. Putting the a.s.o. before everything removes the pressure from the system.

rajdude · Jun 9, 2022

Biglew11 said:
Both set ups will work. But putting the a.s.o. in the waste line keeps the filter canisters at house pressure. Putting the a.s.o. before everything removes the pressure from the system.

Ah! so what you are proposing is a THIRD way of connecting the ASO....in the inlet supply line, even before the carbon blocks.

May I ask why is keeping the canisters not under pressure advantageous? I guess it will help if a canister bursts or develops a leak?

Biglew11 · Jun 9, 2022

rajdude said:
Ah! so what you are proposing is a THIRD way of connecting the ASO....in the inlet supply line, even before the carbon blocks.

May I ask why is keeping the canisters not under pressure advantageous? I guess it will help if a canister bursts or develops a leak?

If you have better incoming pressure, say 80 psi my opinion is it's better to remove that pressure when you can. However they are designed so that they can handle it.

It will also allow you to change out the filters that are before the check valve.