The safety technique does not stop and the preserved steam locomotives needs to stay equal to the standards of today. In some occasions it is hard to catch up with these standard rules of safety and steam locomotives has to be adapted to these modern standards as well.
The Indusi device at the right with two buttons on top. A mouse operated switch for overruling and a switch for deblocking.
An air cylinder will force the regulator to cut off when the emergency brake kicks in, but will not close the regulator completely to keep some steam in the cylinder blocks.
Indusi / PZB Germany
Indusi is a point-to-point signalling transmission, This system was already present in the steam era and was build at every steam locomotive throughout Germany. A powered magnet with a single frequency or multi frequency was beamed up to a magnetic receiver that was installed at the engine or tender. The signal just knew three different frequencies:
500 Hz for distance or approach speed limiter
1000 Hz at distance and approach at main signals
2000 Hz for a overrunned signal causing an emergency stop