Pressure Control for Reverse Osmosis Systems

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.

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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