Actuation of a fluid-based device by a solenoid with a stroke that is transferred directly to the device and triggers there an actuation (e.g. switching directional valve) (Figure E 24). In this way the solenoid becomes an important interface between the electrical (electronic) and the hydraulic part of a device or system.
Solenoids must be kept as small as possible for reasons of cost effectiveness. They are a very important cost factor in electro-hydraulic devices.
The force and distance of the stroke are, however, dependent on the size of the solenoid coil and the armature due to the basic laws of electro-magnetics. For this reason these days, for instance directional valves are generally only actuated directly by solenoids up to a nominal size 10 (Figure E 24 b). With DC solenoids it is possible to shorten the switching time by means of fast excitation or over-excitation.
Figure E 24: Solenoid actuation; a) layout, b) limits of direct actuation