Piston type energy recovery device (ERD) commonly depends upon the concerted actions of magnetic sensors and PLC controller to realize the energy recovery function. For ensuring operational stability and flexibility of the device, signal control mode is basically adopted in the standard PLC controller. However, as a typical emergency condition of the signal control mode, failure of the magnetic sensor may bring on function loss of the mode, which imperils the operational safety of the ERD and even the RO system. So in this paper, an optimized PLC control strategy with fault tolerance module is developed to resolve the possible control problem of piston-type ERD. The experimental results indicate that the optimized PLC control strategy can maintain reliable under simulated emergency condition of magnetic sensor failure. (C) 2014 Elsevier B.V. All rights reserved.