In the case ol the stroke-controlled solenoid (Fig 10). the position of the armature is controlled by a ciosed-loop control circuit and maintained irrespective of the counter-pressure. provided it is within the rated working range of the solenoid.
With the stroke-controlled solenoid, the spools of proportional directional, flow as well as pressure control valves can be directly operated, and be controlled in any stroke position The stroke ot the solenoid is between 3 and 5 mm depending on the size.
As already mentioned, the stroke-controlled solenoid is primarily used for directly operated 4-way proportional valves.
In conjunction with the electncal feedback, the hysteresis and the repetition error of the solenoid are maintained with very tight tolerances. In addition, any flow forces. which occur at the valve spool are compensated (or {relatively small solenoid force in relation to the interfering forces).
In the case of pilot operated valves, the controlled hydraulic pressure is applied to a relatively large control area. The available positioning forces are therefore considerably greater and the percentage effect of interfering forces is not so marked. For this reason, pilot operated proportional valves can be implemented without electrical feedback.
