Reverse osmosis - tank pressure?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by jpb116, Jun 11, 2009.

  1. jpb116

    jpb116 New Member

    Messages:
    37
    Location:
    Massachusetts
    Hi all. what is the best pressure to charge a RO holding tank too?
  2. 99k

    99k Radon Contractor and Water Treatment

    Messages:
    460
    Location:
    Fairfield Co.,Connecticut
    Typically 6-8 psi
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,311
    Location:
    Cave Creek, Arizona
    psi

    The lower it is the more water it will hold. The system itself will establish the operating pressure.
  4. Gary Slusser

    Gary Slusser That's all folks!

    And the lower it is the faster the draw down gals are used up and the membrane starts making water, and flow goes to next to nothing; dribbles actually.

    The air pressure should be set at what the manufacturer suggests; which is usually 7-10 psi with no water in the tank.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,311
    Location:
    Cave Creek, Arizona
    pressure

    Not really. The air charge will be at system design pressure when the membrane shuts off. The water will then discharge at exactly the same rate regardless of the initial charge. BUT when the water usage drains the tank down to the manufacturer's recommendation the tank will be empty and water will cease flowing. If the charge was actually less than that the water will continue to flow at a slower rate until the tank is empty.
  6. Gary Slusser

    Gary Slusser That's all folks!

    Yes really.

    The water flow reduces as the tank empties because the pressure reduces to 0 psi, the same as a well pump pressure tank does.

    When the tank empties the output of the membrane trickles out the faucet instead of going into the tank. It only goes into the tank when the faucet is shut off.
  7. kagtha

    kagtha New Member

    Messages:
    1
    Location:
    Virginia
    Tank Pressure problem?

    Yeah I had a similar issue. What Gary said may be simple but it was my first installation so I was not thinking straight. I didnt have very good water pressure, i finally figured out that the tank needed back pressure to work (the faucet in the off position) Duh
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,311
    Location:
    Cave Creek, Arizona
    IF the pressure is TOO above the system pressure, the RO unit cannot push any water into the tank, so you get ZERO volume from it and the only flow is from the membrane. If the pressure is ZERO, the tank will be full of water but there is no air to push it out, so you only get the water flowing from the membrane. Under ANY other situation the system will compress the air to its working pressure and it will deliver water until the air pushes all the water out of the tank, at which time the flow will diminish. The higher the pressure the LESS water the tank will hold, and vice versa, but it will be at the precharged pressure at the time it stops flowing.
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