THE SPECTRA CLARK PUMP
The "Clark Pump" is an energy recovery and pressure amplification innovation developed manufactured by Spectra. It is powered by a flow of relatively low-pressure water from a separate pump (well or feed-water pump). The Clark Pump boosts the pressure of the feed-water to the reverse osmosis membrane (800 PSI).
The Clark Pump is used in all of the desalination units.
For a more technical explanation please refer to the AWA Journal Article
This is the Clark Pump function diagram.