RO REJECT VALVE

Published on by in Technology

Hi! Can anyone help me understand how to size RO reject valve properly? Is their any sizing calculations applied  if we know the flow rate of reject?

Thanks 

Taxonomy

5 Answers

  1. Keeping "safety in design" principals foremost, it is better to avoid a control valve and use a multi-stage orifice. This avoids the hazards that can arise if the the valve is operated incorrectly. Typically, there is low pressure pipework after this point so there is a serious "loss of containment" hazard if the discharge flow/pressure is too high. 

    Given the fluid specification, connection details, flow rate and required pressure drop, a reputable supplier (e.g. https://www.rototherm.co.uk/pdfs/104.pdf ) will be able to size a multistage orifice for you.

    I trust this is of assistance. 

    H

  2. Control valves are normally rated by a function referred to as Cv.

    Cv is calculated (in imperial units) as:

     

    Cv= Flow * sort( SG / DP)

    where : flow (gallons per minute), SG = Specific Gravity, DP = Differential Pressure (pounds per square inch). 

    I am certain you can find equivalent formulas using metric units.

    So if you need 300 psi on the concentrate side of the membrane and have a concentrate specific gravity of 1.02, you can easily determine the Cv required for the valve to handle this flow.

    I typically calculate both a wide open (very low DP) value and a normal operation condition (relatively high DP) and then start looking  for a valve that will provide a full open Cv to handle the low DP condition and an 70-80% closed position that will handle the high DP situation. In some cases you will not be able to get a valve that will open enough to allow the low DP condition and you will need to consider adding a bypass valve for low DP conditions such as membrane rinses and cleaning cycles.

    1 Comment

    1. Hi, thanks for replying to my question on RO reject valve. Your reply is useful. I have many books pertaining to Membrane systems but none of them explains the mechanical design engineering aspect of key components including valve sizing and selection for valves reverse osmosis systems. If somebody can write a e ok on this it will help engineers working on desalination projects. I am looking at process control or effectively and remotely controlling the RO recovery automatically  using automatic valves for reject and reject recycle.

      thanks and regards 

      Raman

      Ionic Engineeing technology Pvt. Ltd.

  3. Dear Prof KV Raman.

    This is an important factor ie sizing and design of RO Reject water parametrs.

    If you desire RO water to be of least TDS ppm then the flow would be maximum, and this needs to be done by selecting the right operating pressure on the RO Membaranes.

    If the process can have the maximum TDS ppm on Reject water released would be very minimum and hence the observance of higher salinity.

    Here too the appropriate operating pressures are applied.

    The above may be kept noted, for designing athe reject water-flows in a RO water-process.

    Well wishes.

    Prof. Ajit aSeshadri. INDIA .

    1 Comment

  5. Good Morning Mr. Iyer,

    The size of the valve depends on the system flow rate and the specified brine to product ratio required in accordance with source water analysis, temperature and pressure.   A problem arises when the operator attempts to produce more RO water by reducing the brine flow resulting in membrane scaling and ultimately membrane failure.

    Aquathin's Multi-Barrier RODI Systems (25 gpd -24,000 gpd) brine reject valves are built preset with intentionally preventing the operator to manipulate.

    Warmest regards,

    FOR THE BEST TASTE IN LIFE

    Celebrating 40  Years Pure Excellence

    ...into another Half Century re-inventing the water industry !

    Think Aquathin...AquathinK !

    ( visit the all new www.aquathin.com )

     

    ** AN ISO9001:2000, ISO9001:2008 , ISO9001:2015  QMS REGISTERED / CERTIFIED COMPANY - (IMS 0192, NQA 12635) **

    & 2008 PRESIDENT'S E STAR AWARD RECIPIENT ( visit www.aquathin.com/estar2008.pps  )

     

            Alfie

    Alfred J. Lipshultz

    President & CEO

    Aquathin Business Center  /  950 South Andrews Avenue / Pompano Beach, FL  33069

    T 954 781 7777 / F 954 781 7336 /E info@aquathin.com  / Skype aquathinhq.alfie

    1 Comment

    1. Hi, thanks for replying to my question on RO reject valve. I have many books pertaining to Membrane systems but none of them explains the mechanical design engineering aspect of key components including valve sizing and selection for revers osmosis systems. If somebody can write a e ok on this it will help engineers working on desalination projects.

      thanks and regards 

      Raman

      Ionic Engineeing technology Pvt. Ltd.