Digital Interface Valve with an Integrated Microprocessor and Fieldbus Communications

Moog Inc. has developed a new hydraulic valve platform, Digital Interface Valves, with microprocessor based electronics and a CANOpen fieldbus. These new valves can replace analog technology and offer configurable functions that enable customers to define the dynamic behavior of the valve and adapt its characteristics to particular application requirements, while providing high-precision digital flow and pressure control. These valves are central to implementing a distributed control concept in a machine because tasks can be assigned to local devices rather than the main control device, providing our customer’s machines with increased flexibility and functionality.

The Direct Drive Servo-Proportional Valve of the Digital Interface Valve (D638 Series) is operating in multiple applications around the world. Prototypes are being tested for other models including the Digital pQ Servo-Proportional Valves (D941 Series) for pressure control and pressure limiting applications. This new product development platform is part of Moog’s ongoing initiative to extend digital intelligence to its most advanced hydraulic and electric motion control products.

Key benefits of Digital Interface Valve products for customers are:

  • CANBus Communication: Diagnostic capabilities, integrated monitoring of key environmental and internal characteristics, and valve parameter modifications can be accessed on-site or remotely.
  • Flexibility: The ability to download parameters via the fieldbus connection or directly from the upper PLC program enables optimum tuning of valve parameters during the machine cycle, even while the machine is operating. The Windows®-based graphical user interface is easy to learn and convenient
  • Cost Savings: Since the pressure control loop is tunable via software, rather than passive electronic components, it is now possible to stock a single valve for multiple applications reducing the need to stock several valve models.
  • Lower Installation Costs: A serial wiring scheme reduces the amount of wiring and improves noise immunity.

Some special benefits of the design of the pQ Servo-Proportional Valve (D941 Series) include:

  • Superior Control: The improved frequency response of the design allow high spool position loop gain, providing excellent static and dynamic response and superior control system performance. The improved valve dynamic performance is due to the extremely high natural frequency of the ServoJet® pilot stage (500 Hz) and the implementation of advanced current control algorithms, which is only possible via digital electronics.
  • Energy Savings: Considerably improved flow recovery (more than 90% of the pilot stage internal leakage flow) contributes to energy savings, especially for machines with multiple valves.


  • Reliability: The high pressure recovery of the ServoJet pilot stage (more than 80% delta p at 100% command signal) provides higher spool driving forces and ensures enhanced spool position repeatability.
  • Safety: Fail-safe versions with defined safe spool position using a spring, a poppet valve or by external supply cut off ensure operator safety.