New reverse osmosis system. Flow rate seems low. Please advise

Discussion in 'Water Softener Forum, problems, installation and r' started by ribs1, Sep 14, 2012.

  1. ribs1

    ribs1 New Member

    Messages:
    17
    Location:
    Ann Arbor, Michigan
    Hey guys,
    I just finished having a reverse osmosis system installed as part of my new kitchen project.
    I bought a black and white unit from pure water products in texas with a permeate pump.

    Everything is working now but I think the flow rate is too low. I have never had one of these system though so I guess I'm not sure what the flow is supposed to be.

    To test, I filled a 1 quart container in 35 seconds. is this normal? What can I do to increase flow rate from my RO faucet?
    Here's some more details
    1. Unit is mounted on a shelf in the basement just under the kitchen cabinet.
    2. All the tubing is 1/4 inch
    3. The tank is mounted just under the RO system.
    4. I think the membrane is a 24 gallon per day.

    Any other tips would be appreciated.
    Thanks
  2. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,048
    Location:
    Maine
    what is the pressure? And...how much water do you expect to get through 1/4" tube
  3. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,826
    Location:
    NW Ontario, Canada
    RO systems are often placed directly under the sink. You can lose about 4 PSI by having it in the basement. The long run of 1/4" tubing doesn't help. A different faucet might make a small difference.
  4. ribs1

    ribs1 New Member

    Messages:
    17
    Location:
    Ann Arbor, Michigan
    I don't know how much water should come through a 1/4 inch tube. I don't really know how to measure my pressure.
    I guess I could look at the pressure gauge by my well pressure tank?
    Should I change this whole thing to 3/8" tube and fittings?
  5. ribs1

    ribs1 New Member

    Messages:
    17
    Location:
    Ann Arbor, Michigan
    The unit is on a shelf high on the wall in my basement pretty close to the ceiling directly under the sink cabinet. I didn't really have much room in the sink cabinet because I have a large apron front sink. I could have gotten it in there though.
  6. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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  7. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,048
    Location:
    Maine
    Somewhere in the paperwork that came with the unit there should be a chart that shows the volume / pressure chart etc for the unit.
  8. Gary Slusser

    Gary Slusser That's all folks!

    Doesn't seem to be anything wrong except customer volume expectations are not met.

    The size of the tubing or the basement install is not a problem.

    There is no way you can lose 4 psi in the distance from the basement to the faucet on the kitchen sink counter, well a kink in the tubing would do it but not by the length or dia/size of the tubing.

    Most under sink ROs I am aware of use 3/8" tubing from teh tank to the faucet but..... You can not use larger dia tubing and get more water because the faucet is 1/4" and the captive air pressure in the RO storage tank provides the pressure to the faucet which should be about 7-10 psi.

    The RO has to work against that pressure so you don't go any higher without severely decreasing the output volume of RO water and the time it takes to produce it.

    To get more product water in a shorter period of time you'd need a larger than 24 gal/day membrane. Or to add a pump.

    In the manual there should be instructions on how to check that air pressure. You do it with a regular tire pressure gauge and with no water in the tank.

    The well pump pressure switch setting has nothing to do with the pressure coming out of the RO's storage tank.
  9. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,826
    Location:
    NW Ontario, Canada
    In case you forgot, the formula is .43 PSI per foot just for the static column alone and the OP did not say how high in the basement the system was installed. There is also losses per foot on a long 1/4" tubing run, also not mentioned in the OP.

    So, there is a way you can lose 4 PSI.
  10. Gary Slusser

    Gary Slusser That's all folks!

    Well the RO won't be sitting on the basement floor because that would not allow servicing it, and usually the tank is up on the wall above the RO. Main line water pressure moves the water into the storage tank.

    So how many feet of height do you think there is from the storage tank to the faucet? To lose 4 psi there would have to be over 8' of height to the faucet. A basement is usually 8' and kitchen counters are usually 33"-36" but...

    As I said, the captive air pressure in the RO's storage tank provides the water pressure to deliver the product water to the faucet.
  11. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,826
    Location:
    NW Ontario, Canada
    Looks like you answered your own question but you forgot to factor another foot for the floor joists. :p
  12. ribs1

    ribs1 New Member

    Messages:
    17
    Location:
    Ann Arbor, Michigan
    Hi Fellas,
    The RO unit is close to the basement ceiling. The tank is mounted just beneath the unit. Both are high up on the wall. It is not far to the sink cabinet and up to the faucet.
    It is likely that the problem is just that I am not used to these things. I have never owned one before.

    Also, after letting the system sit idle over night the performance is better today. I just filled that same quart container in 25 seconds.
    I guess I just didn't let the tank get full before testing.
    I do have a permeate pump

    Anyway, just curious, what is a typical flow rate out of these things? Am I worried about nothing?

    Thanks
  13. mialynette2003

    mialynette2003 Member

    Messages:
    720
    Location:
    Ocala, Florida
    I think you are worried for nothing. You are dealing with a 1/4" line that goes uphill and the more water that is drawn from the unit, the less flow rate you will have. A qt in 25 sec would be normal to me. Enjoy the great taste, less filling (pun intended) RO water. LOL
  14. ribs1

    ribs1 New Member

    Messages:
    17
    Location:
    Ann Arbor, Michigan
    We are definitely enjoying the water and I am getting used to the flow rate.
    Really I had no problem drinking our water out of the softener but my wife hated it.
    I am very happy to not have to buy bottled water anymore.
    Ice cubes look nice too. Really clear.

    Coffee was good this morning too.
  15. ditttohead

    ditttohead Water systems designer, R&D

    Messages:
    1,789
    Location:
    Ontario California
    Ro tank pressure shoud be set to 6 psi empty. The only way to test the tank pressure is when it is empty of water. If anyone tells you otherwise, they are wrong.

    Your RO systems pressure is directly affected by line pressure. Adding air to the tank will not increase pressure to the faucet. At least not for the first half gallon. It will only lessen the tanks volume. The permeate pump shoud be installed without an ASOV, or at minimum, a 90% ASOV.

    The tube length is always of great concern to flow rate avaiability. It has to do with frictional loss and capillary restriction calculations. I would recommend running any RO line between the tank and the faucet in 3/8" if it is more than 10', 1/2" if it is over 20'.

    Hope this helps.

    FYI, the flow rate should be approximately .5 GPM if the system is operating properly. Most faucets will flow at approximately 1 GPM. The loss of flow from the posy filter, tubing length, etc. can drop you to the 1/2 GPM range. This is fine since contact time is key for the post filter to provide the best tasting water.
  16. ribs1

    ribs1 New Member

    Messages:
    17
    Location:
    Ann Arbor, Michigan
    Thanks for this information Dittohead, and thanks for everyone elses help too.
    As you guys can probably tell, I am not a plumber or a water treatment pro as many here are. I am must a consumer trying to educate myself as much as possible.

    1. I am pretty sure that there is an ASOV on this system, however, I will go and make sure. I'll check out the manual and call the dealer if possible.
    2. I can measure the tube length from the tank to the faucet. I am pretty sure it is less than 10 feet though.

    Another question, Do these things have a break in period? I just measured flow rate again today and it seems even better. Filled the same quart container in 23 seconds. I guess that is a little better than .5 gpm which according to you guys is pretty good.
  17. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,245
    Location:
    Cave Creek, Arizona
    RO units have their own pressure and it has nothing to do with the regular house pressure, regardless of whether it is a pump or city system. The flow rate is ALWAYS "low". It is a combination of the low system pressure and the small tubing size.
  18. ditttohead

    ditttohead Water systems designer, R&D

    Messages:
    1,789
    Location:
    Ontario California
    I am not sure where you got this information. please allow me to correct it. This is a common misconception. FYI, I do training on this topic regularly and to many of the large OEM and distribution houses.

    A standard RO design with an ASOV will shut off the system when it reaches 60% of line pressure. So.. an incoming pressure of 60 PSI will = a maximum ro water tank pressure of 36 PSI.

    An RO with a Permeate pump will typically shut off at 96% of line pressure, so the same 60 PSI water will yeild 58 PSI of tank water pressure.

    An RO with a proper ASOV will shut off at 90% of line pressure. So the same 60 PSI will yield a tank pressure of 54 PSI.

    The air on the bladder will be equal to the water pressure, simple physics.

    As the water is used from the tank, the air pressure pushes out the water and as the air decompresses and loses pressure, so does the water pressure out of the tank. Simple physics, equal pressures...

    The only exception to this would be an RO system with a booster pump. The booster will typically pump the water to 60-80 PSI depending on the internal bypass setting, then, regardless of incoming pressure (assuming ou have adequate flow) the system will produce the same amount of water reagardless of incoming pressure. Booster pumps are not needed for most smaller resdiential style systems, and should be avoided if possible. They are necessary sometimes due to excessive tds, lower temperatures, low incoming pressures, or a combination of these problems, but in general, are not needed.
  19. ditttohead

    ditttohead Water systems designer, R&D

    Messages:
    1,789
    Location:
    Ontario California
    The systems should be allowed to fill and be fully drained 2-3 times for the first day. After that they are ready for use. Per the membrane manufacturers literature, the membrane does have a 72 hour start-up/wetting time. This is for critical applications where the 99.2% rejection rates are checked, regulate, and monitored, like for USP or WFI installations. For resideantial, 24 hours is fine.

    If the system has an ASOV, make sure it is a 90% ASOV, not the standard 60%. The company you purchased it from should know which one they use. The 60% makes no sense and takes away the primary function of the Permeaterpump, high available water pressure, and more water volume in the tank.

    The inventor of the permeate pump personally recommends no ASOV. The only time an ASOV should be used with a PP is when there is very low water usage. This can be countered by simply using more water, or purging the system weekly. Most residential applications use plenty of water for a PP.

    Hope this helps.
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