Most automatic systems employ electric solenoid valves. A solenoid valve has two main parts&colon; the solenoid and the valve. Modern service valves incorporate an electric shut-off solenoid. A rotary voice coil is a rotational version of a solenoid. The core or plunger is the magnetic component that moves when the solenoid is energized. Repeated actuation of the rotary solenoid advances the snap-switch forward one position. A reed relay is a reed switch enclosed in a solenoid. In 1910, ASCO Numatics became the first company to develop and manufacture the solenoid valve. German cars had a solenoid operated variable pressure windscreen wiper. EGR Solenoid, Purge Control Solenoid, etc. The solenoid tends to attract the piston or projectile towards the middle of the solenoid. The same trend is true for solenoid coils. Alternatively, an electro-mechanical oscillator driven by an AC-energized solenoid may be used. In Figure 2, a flyback diode was added in antiparallel with the solenoid. The maximum pull is increased when a magnetic stop is inserted into the solenoid.