The digital valve system is an on/off valve based directional flow control valve capable of accurate control of hydraulic actuators. The presented system has good features concerning fault tolerance since it can detect, diagnose and compensate faults on-line. This paper concentrates on fault compensation when a valve has jammed in the open – position and the system has internal leakage. The system can adapt to the fault and continue operation with only a small degradation in performance. This feature is unique in the area of hydraulics since the system has no extra components added. The cost for this compensation is increased calculation in the controller and increased energy consumption if a fault occurs. If these downsides can be accepted the system can be considered fault-tolerant and it could be used even in critical applications where failing is not an option. Fault tolerance can also be introduced as standard in every modern hydraulic application where good performance and fault tolerance are needed.

Keywords:digital hydraulics, valve faults, compensation