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Thread: RO Membrane Replacement and Low Storage Capacity?

  1. #1

    Default RO Membrane Replacement and Low Storage Capacity?

    Recently my kitchen sink RO system was not producing very much product water (about 4 cups overnight) before the RO water is depleated from the tank. I decided to take a look at things. I replaced the two pre-filters in the canisters, emptied the storage tank and set the empty pressure to 8 psi (with valve closed). This was my mormal maintainance routine every 6 months.

    When I turned on the water and let it fill up overnight, it only produced about 4 cups of water. The storage tank feels really light. I removed the drain line from the sink and put it in a bucket. When I turned the system on again, I saw a lot of water coming out of the drain tube (low pressure, but constant flow). I did nto see any procuct water being produced. I thought maybe the ASOV might be bad so I bypassed it and just ran the RO membrane output to the permeate pump directly. Same thing, lots of drain water, no product water. Also, the permeate pump (ERP-1000) is not making lots of clunking noises like it normally does (maybe once every 5-10 minutes now). If I remove the line to the Permeate pump permeate input, no water flows out from the RO membrane housing. If I remove the check valve from the RO membrane housing, then water will slowly drip out. Does anyone have any ideas here?

    Here is how my RO system is set up.
    • Input water -> sediment filter (canister 1) -> carbon filter (canister 2) -> ASOV high pressure side -> RO membrane housing cap ->
    • RO membrane housing product water -> check valve -> flow reducer? -> permeate pump permeate in -> permeate pump permeate out -> storage tank t-fitting -> post filter -> faucet
    • RO membrane housing waste water -> 400 flow meter -> permeate pump brine in -> permeate pump brine out -> sink drain

    It looks exactly like Figure 5. Then I removed the ASOV and now it looks like Figure 6. RO schematic (Aquatec permeate pump installation)

    I noticed a metal check valve at the output of the RO membrane housing. Is this something that needs to be serviced/replaced. Is is even necessary?

    I also took the membrane out to see what kind it was so I could order another one if I needed. It said TW2012-60AP. I searched the internet and could not find a listing for it. Are there any recommendations for good quality replacement membranes? What other items should I replace while I'm ordering parts?

    Last edited by Flat Panel; 03-01-2013 at 02:13 PM. Reason: fix link

  2. #2


    You do want a check valve in the RO membrane permeate port or if not in the port then in the tubing just downstream. Is the check valve stuck closed?

    When permeate (RO water) production drops the most common cause is that clogged prefilters (all the filters that touch the water before it reaches the RO membrane) are clogged and stealing pressure from the membrane.

    Are your prefilters clogged?
    Do you have a pressure gauge on your system? What does it read? Is the gauge installed to read pressure after the prefilters but before the membrane?

    Pressure tanks also go bad. If you open the faucet and get about a half galss at normal pressure and then just a drible, it may be that the bladder in the tank is bad. This is not uncommon. Solution is to replace the tank.

    We'd need to see a picture of your RO membrane housing to be sure, but chances are you could just replace your membrane with an industry standard TW1812-50. Your 400 ml/min flow restrictor is ok to use with a 60 gpd or a 50 gpd membrane.

    Buckeye Field Supply

  3. #3
    DIY Senior Member mialynette2003's Avatar
    Join Date
    Nov 2010
    Ocala, Florida


    The membrane has to have back pressure to produce water. The devise to achieve the back pressure is a capllary tube. If it gets clogged, it will not allow the flow. You may want to replace it. The membrane could be at fault as well. How old is it? They normally last 3-5 years even though I have seen them last longer. The permeate pump works on hydraulics. One chamber is for the drain water and the other is for the product water. Once the drain side fills up, it forces the product water into the tank and then the product water can fill the chamber again. BTW, when filling the air pressure in the RO tank, the valve should be open.

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