The biggest proportion of the cost of desalted water is the energy consumption, especially for small-scale SWRO desalination system. In order to decrease the cost of desalted water, the energy recovery device is preferred to be considered in small-scale SWRO desalination system. However, the investigation of energy recovery device for small-scale SWRO system is scarce. Until now the design of energy recovery device has not been based on the results of the mathematical simulation but almost on experimental and empirical knowledge, and there are few detailed reports about the optimal design of energy recovery device for small-scale SWRO desalination system in previous articles. In the current paper, a hydraulic energy recovery (HER) device with novel mechanics is introduced, the detailed simulation results of the HER device and specific energy consumption of small-scale SWRO system equipped with the HER device are presented. The simulated results are very useful for optimal design of the HER device and its coupling SWRO desalination system. (C) 2009 Elsevier B.V. All rights reserved.