Pressure Control for Reverse Osmosis Systems -

Pressure Control for Reverse Osmosis Systems

Reverse Osmosis

  • Schematic of Equilibar controlling pressure in Reverse Osmosis
Reverse osmosis is a separation process that is used primarily in desalination and water purification processes. Osmosis is similar to diffusion, but where the molecules are water and are traveling across a semi-permeable membrane. The membrane allows small molecules to pass and blocks larger molecules, just as a filter does. The water molecules naturally travel from low to high concentration like in diffusion.

In reverse osmosis, the water travels from high concentration to low concentration, but because that does not happen naturally, pressure must be applied to the high concentration side of the membrane to force water molecules to the other side. This flow through a reverse osmosis membrane (RO membrane) is how desalination and water purification take place.

Schematic of Equilibar controlling pressure in Reverse Osmosis

In the schematic above, an Equilibar back pressure regulator (BPR) is used at the outlet of the retentate side of an RO membrane to apply pressure for the reverse osmosis process. There is a natural pressure across the RO membrane in the direction of low concentration to high concentration called the osmotic pressure. In order for reverse osmosis to take place, the applied pressure on the retentate side of the RO membrane must be greater than the osmotic pressure.

An Equilibar BPR, with its dome loaded multiple orifice technology, provides precise and consistent pressure for the reverse osmosis process even if the feed water experiences variable flow rates. The required pressure for reverse osmosis to proceed is set by the electro-pneumatic pilot regulator which delivers the exact setpoint in a 1:1 ratio to the dome of the Equilibar BPR.

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EQ EPR3000 mounted on EQ BPR web
An Equilibar GS Series back pressure regulator (BPR) is shown above with an electronic pilot regulator. Using an electronic pilot to control an Equilibar BPR makes it easy to automate pressure control. This is particularly beneficial when pressure setpoints in an RO system vary from time to time and computer control is designed into the system.


Equilibar back pressure regulator used in Reverse Osmosis System by Convergence Technologies B.V Convergence Industry B.V. uses an Equilibar BPR in their RO System.

Membrane Fouling

When microorganisms adhere to the membrane in an irreversible process, it is called RO Membrane Fouling. This prevents the water from flowing properly and the effectiveness of the reverse osmosis process declines. This is a battle that RO scientists face regularly.

At the Massachusetts Institute of Technology, doctoral candidate Emily Tow and other researchers were developing a model to predict membrane fouling in order to find solutions to the problem. Understanding the fouling of the membrane used in RO desalination will make it possible to reduce the overall cost of water treatment and expand access to clean drinking water for people throughout the world. As part of this effort, MIT researchers used an Equilibar back pressure regulator to control the differential pressure across RO membranes, allowing higher resolution in fouling measurement. Read the article here.

For more information about how Equilibar fluid control products can help with your research or manufacturing process, contact an Equilibar application engineer.

MIT case study on membrane fouling

Equilibar back pressure regulator used in MIT reverse osmosis membrane study on fouling


GSDH6 General Service Back Pressure Regulator

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