The D680 Series Proportional Flow Control Valves are throttle valves for 2-, 3-, 4- and 5-way applications.

These valves are suitable for electrohydraulic position, velocity, pressure, or force control systems, including those with high dynamic response requirements.

With the new D633 Series directly driven pilot valve (DDV), a further important step has been made in the direction of robustness and energy saving. This linear force motor driven pilot valve is developed as a variant of the proven Moog DDV Series.

The integrated electronics of the D680 series is also a new development featuring SMD technology, and requires 24 V DC power supply.

• A direct drive pilot valve requires no pilot leakage flow. This results in considerable energy savings, especially for systems with multiple valves.
• The dynamics of the direct drive valve is nearly independent of the operating pressure.
• Reliable operation. The excellent pressure gain of the pilot valve with spool / bushing, provides high spool driving forces to the long stroke main spool. This ensures enhanced main spool position control even with high flow forces and contaminated fluids.
• Excellent dynamics based on a high natural frequency allows high main spool position loop gain, resulting in extremely good static and dynamic response of the main valve.

• Valve body for high rated flow, optional with external pilot supply using X and Y ports.
• Reduced spool drive area with D683 and D684 Series results in the following advantages:
• improved dynamic response
• reduction in pilot fluid flow for fast movements of the main spool.
• Fail safe versions available with defined safe spool position using a spring and a 4/2-way solenoid valve for control flow short circuit.
• The D680 series proportional control valves are of two-stage design. By combining a fast first stage, suitable main spool drive area and integrated electronics, an optimum proportional valve can be offered.

The D633 Series pilot valve consists of a permanent magnet linear force motor, a drive rod connecting motor armature and the spool guided in a bushing. The linear force motor contains a coil, permanent magnets, pole pieces, an armature and a centering spring arrangement.

The 4-way spool controls fluid flow from the pressure port to one of the load ports, and also from the other load port to return. Deflection of the centering spring due to spool displacement, provides a return force for the armature.

An electric current applied to the coil of the linear force motor produces an electromagnetic flux depending on the current polarity. This electromagnetic flux is superimposed on the permanent magnetic flux in the air gaps between armature and pole pieces. This results in a polarity dependent displacement of the armature against the centering spring force.

The spool being connected to the armature by a rod shares the armature motion. Flow forces acting on the spool due to the fluid flow through the valve, and friction forces between spool and bushing due to contaminated fluid, are overcome by the force motor. The position of the spool is approximately proportional to the coil current.

The position control loop for the main stage spool, position transducer and pilot valve is closed by the integrated electronics.

An electric command signal (flow rate set point) is applied to the integrated position controller which drives the current in the pilot valve coil.

The position transducer (LVDT) which is excited via an oscillator, measures the position of the main spool (actual value, position voltage). This signal is then demodulated and fed back to the controller where it is compared with the command signal. The controller drives the pilot valve until the error between command signal and feedback signal is zero.

Thus, the position of the main spool is proportional to the electric command signal.