After switch-on, the current rises relatively slowly until it reaches the constant holding current. The armature forces in DC solenoids are below tube of AC solenoids with the same coil size (number of windings and wire diameter), i.e. they are able to switch only lower media pressures than AC solenoids with the same nominal diameters. Nevertheless, DC solenoids are important as valve actuators, since a number of control devices (e.g. PLCs) emit DC signals which can be used directly for control. One other area of application relates to battery-operated valves, which can be used if there is no mains power supply or special power supply units, or if a such a supply would be very complex or costly.