my APEC reverse osmosis system is making a constant dripping or dribbling sound from the drain line. is that normal?

Diagnosis

The APEC ROES-50 utilizes a process where a significant amount of "brine" or wastewater is pushed through the membrane to flush out contaminants. If you hear a periodic, slow trickle or a rhythmic dripping sound while the system is actively producing water (i.e., when the storage tank is empty or being depleted), this is perfectly normal operation. The system is designed to continuously discharge waste water into the drain line during the filtration cycle to prevent the RO membrane from fouling. However, if the dripping or flowing sound is constant and never stops—even after the storage tank has been completely filled and the faucet is closed—you have a failure in the automatic shut-off mechanism. This usually occurs because the Automatic Shut-Off Valve (ASOV) is not receiving enough back-pressure from the storage tank to trigger the internal diaphragm to close the feed water. This results in the system "running away," where water flows continuously through the membrane and out the drain, wasting gallons of water and prematurely wearing out your pre-filters and membrane.

How to Fix It

To stop a continuous leak from the drain line, you must ensure the system can reach the required shut-off pressure. Follow these steps to diagnose and resolve the issue:

1. Verify Tank Pressure: Turn off the incoming water supply valve and close the tank valve. Open the RO faucet to bleed off all remaining pressure. Use a tire pressure gauge on the air valve (Schrader valve) located at the bottom or side of the storage tank. The pressure should be between 5 and 7 PSI when the tank is empty. If it is lower, use a bicycle pump to add air until it hits 7 PSI.
2. Check Incoming Water Pressure: Ensure your home's water pressure is at least 40 PSI. If you have a pressure regulator on your main line that is set too low, the ASOV will never trigger. If pressure is below 40 PSI, you will need to install a permeate pump or a booster pump to force water through the membrane.
3. Test the ASOV Valve: Locate the ASOV (the small square plastic valve where four tubes connect). While the system is running, slowly close the tank valve. If the flow to the drain stops immediately, the valve is working, and the issue is likely a faulty tank bladder. If the flow continues even with the tank valve closed and the faucet shut, the ASOV diaphragm is likely ruptured.
4. Replace the ASOV: If the valve is faulty, disconnect the four 1/4" polyethylene tubes. Install a new ASOV (Part #APEC-ASOV) ensuring the tubes are pushed firmly into the fittings to avoid leaks.

If That Didn't Work

• Check the Check Valve: There is a small one-way check valve located at the exit of the RO membrane housing. If this valve fails or gets stuck open, water will leak back from the tank through the membrane and out the drain line. Replace the check valve if you notice the system "cycling" (starting and stopping) every few minutes.
• Inspect the Flow Restrictor: If the dripping is excessive but not constant, the flow restrictor (the small plastic plug in the drain line) may be clogged or cracked. A faulty restrictor alters the pressure balance, preventing the ASOV from closing. Replace the 300cc or 400cc restrictor depending on your specific ROES-50 model variant.
• Examine the Membrane Seal: If the RO membrane is not seated correctly in the housing, water can bypass the membrane and flow directly into the drain line without creating the back-pressure needed to shut the system off. Open the membrane housing, remove the membrane, and re-seat it firmly, ensuring the O-rings are lubricated with food-grade silicone grease.

Heads Up

• Air Traps: After replacing filters or the ASOV, you may hear "gurgling" sounds. This is normal air trapped in the lines; run the system for 2-3 full tank cycles to clear it.
• Filter Change Schedule: Always replace the three pre-filters every 6 months. Clogged pre-filters drop the incoming pressure, which can mimic a faulty ASOV by preventing the system from reaching shut-off pressure.
• Leak Detection: Check the fittings around the ASOV and the drain saddle clamp every few months. The constant vibration of the waste line can occasionally loosen the saddle clamp on your waste pipe.