RODI Help

[xabo]

Installed a normally closed solenoid on my RODI unit to control the booster pump. With the solenoid and pump unplugged, feed water continuously flows thru the pump. Any thoughts?

[Origami]

Is this a solenoid valve on the output side of the pump or the output side of the RO/DI unit? Are you getting flow through your RO/DI waste water line?

[xabo]

Output side of the pump. Yes was getting flow through waste water line. 

[Origami]

Strange. It should be closed.

 

If you open the output side of the solenoid open, can you confirm that the water is flowing from the solenoid and not being siphoned from the RO/DI unit? Is the booster pump off, or running continuously?

 

 

[xabo]

Yes water is flowing from the solenoid and the pump only runs when solenoid is open. The pump is a Aquatec cap 8800. Removed the solenoid and installed the pressure switch from the kit. Pump shuts off when the ATO sensor (Avast) activates but water continues to flow from both the waste and output lines.

 

When I shut off the feed water, the water then drains from the first (Sediment) filter housing through the waste water line. Could a hole/break in one of the tubes or a bad check valve on the RO membrane housing be the cause?

[Origami]

Sorry for the delay. It sounds like the booster pump still passes water even when it's off. As long as there's enough pressure, then, going into the RO/DI stages, it can trigger the ASOV to open and you'll see water flow through the waste line and probably, in low pressure situations, a drizzle through the pure water output side.

 

I can't quite picture the relationship of the solenoid valve, water source, booster, RO/DI stages, etc.  It was a few years back, but I think that I had the same issue that you're seeing. The way I addressed it was kind of brute force: I put the solenoid valve right before the input side of my RO/DI membrane and after the two pre-filter stages. That guaranteed that, when the solenoid valve was off, no pressure was put on the membrane.