Air gap faucet on RO making noise
 

My gf's RO system makes noise like an open car window on the highway.

I've checked tube routing, drain, and can't begin to make it stop. Other than taping over the hole, is there anything else that I can try?

Does it have a holding tank? Check the pressure on the holding tank. It should be 6psi.

It is a Schrader valve, if water comes out then the bladder is shot. A new tank can be purchased.

You are an also fix the pressure on the tank. See this VERY DRY and drawn out video.

https://youtu.be/J4MIWZXHeo0

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An RO water filter makes about 3 gallons of filtered water out of 8-10 gallons. The surplus is sent to the drain. I capture mine outside and water plants with the excess so I have a good read on this.

The noise is the water being sent to the drain. Not much you can do. I hear it even with the hose going through the outside wall into my storage tank.

The noise I'm talking about is air coming through the small hole in the air gap faucet. Not all RO systems use air gap. This thing is loud! I pulled the line out of the drain... the water was running fine, but the noise didn't change.

I put a piece of tape over the hole. Life is much better now. No change in the system operation. I guess if the drain stops up, there's a chance that dirty water could backflow up the drain line, but I think that's a chance we're going to have to take. I guess the better option would be to take the air gap faucet out of the equation and put in a backflow preventer valve. Right now, I'm just relieved that the noise has stopped.

I'll check the pressure on the tank to make sure it's good before considering this issue solved.

I knew what you meant. Sounds to me like make up air. Mine gurgles. Maybe open up the hole first with a felt pipe cleaner and then a drill bit if necessary.