What is Latching type Solenoid Valve?

Latching type Solenoid Valve is also named Bi-Stable Valve or Pulse Valve.
It includes a set of permanent magnets that allow the solenoid to offer hold force even after the power is off.
The term Latching type  is given to this type of solenoid because it has two stable positions.
The first when the solenoid de-energized and plunger is fully extended and second when the solenoid is de-energized and the plunger is held in position by the permanent magnets.
The electromechanical force moves the solenoids from one stable position to the other depending of the polarity of power applied.
A spring can be used to move the plunger out to the extended position as the charge applied only neutralises the permanent magnet force.
Solenoids can only induced electromechanical force in one direction (pulling the plunger towards the endstop).
When the polarity is reversed, it has no effect on the plunger except to neutralise the magnets.
So it's energy saving type .