As known, positive displacement (PD) energy recovery device (ERD) transfers hydraulic energy from the ejected brine of the RO modules directly to the seawater feed and its energy recovery efficiency achieved can be as high as 95% or more. The PD type ERD has been concerned widely in the market place and globally adopted into seawater reverse osmosis (SWRO) desalination plant by designers and operators. Usually, to satisfy the needs of large to super-large SWRO plant capacity, parallel operations of ERD facilities are the most convenient and effective way that can be chosen. In this article, a PD type ERD, named FS-ERD was introduced and a parallel FS-ERD setup was designed and built. Operating schemes for stand-alone operation and parallel operation of the setup were developed and experimentally compared for different test capacity. (C) 2009 Elsevier B.V. All rights reserved.