DDV proportional valves deliver consistent performance

These DDV units feature a proportional valve, at the heart which is a bi-directional, permanent-magnet linear force motor. Moog says that, 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 DDV units are said to offer significantly higher performance than other proprietary valves. This has resulted in their 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 flows at high pressures. In contrast, conventional proportional valves where high-flow and high-pressure performance are demanded face a conflict between stiffness and drive current that cannot always be resolved.

Flat performance curve

Moog has developed a family of DDVs that share this novel linear force motor arrangement. This range covers rated flows (at 5bar per land pressure drop) from 1.9-15.11 l/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 5um have been achieved, one market where the DDV enjoys particular success is in the test market. Mike Baker, Moog's Chief Engineer, 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."