Moog Direct Drive Servo Valve uses Permanent Magnets to provide superior control

Until now, conventional proportional hydraulic valves used in applications where high flow and high pressure performance is demanded, have always faced a conflict between stiffness and drive current. To address this, Moog has introduced a family of high performance yet adaptable products called DDV.

At the heart of most modern hydraulic control systems is the proportional valve and at the heart of the best proportional valves is the bi-directional, permanent magnet linear force motor. With the wide pressure bands and high flow rates commonly used today, it is the performance and capabilities of this type of motor that sets the standard against other designs.

Thanks to the inclusion of a pair of high-energy rare earth magnets, the Direct Drive Valve (DDV) from Moog is able to offer significantly higher performance than other proprietary valves. This has resulted in its use in a huge range of demanding applications. Indeed, the advanced combination of permanent magnets and electromagnetic coils results in spool driving forces considerably larger than those that can be obtained by solenoid coils alone. Lower power consumption provides another potential advantage, with a maximum consumption of just 28.8W.
 
In operation, the electromagnetic coils act as ‘switches’ that divert the permanent magnetic flux paths; effectively acting as an amplifier, but without drawing additional current from the drive electronics.

The result is that the spool position control is ‘stiff’ and well able to counter the flow forces that are created on the spool when the valve is passing high flow rate at high pressure. In contrast, conventional proportional valves where high flow and high pressure performance is demanded face a conflict between ‘stiffness’ and drive current that cannot always be resolved.

Moog has developed a family of DDV’s that share this novel linear force motor arrangement. This family covers a range of rated flows (@5bar per land pressure drop) from 1.9l/min up to 15.1l/min and an interesting feature is that the dynamic performance of the valve is largely insensitive to system pressure, which can be up to 350bar.

As well as many demanding industrial applications, including metal forming machines where accuracies of 5micron have been achieved, one market where the DDV valve enjoys particular success is in the test market. As Moog's Chief Engineer, Mike Baker, explains: "Test is a challenging area where high dynamic response, high flows and high pressures are required. Fidelity of valve response under rapidly changing and severe duty cycles is paramount. The DDV valve provides test engineers with the performance they need to undertake product and system accreditation with confidence."

For further information please call 01684 278249