What is the difference between monostable and bistable valve

Explain how a monostable valve is different from a bistable valve

Difference between Monostable Valves and Bistables:

The Monestables are those who have a stable resting position, which is where the valve will remain indefinitely if the command device does not act on it. Return to the resting position is usually made with a dock; so in the case of a double-position monostable valve, the stable position will be that corresponding to the dock, which is usually placed right by agreement. In the case of three positions, the stable position is central. The bistable valve would have two coils and this valve can be opened or closed by sending a pulse to the corresponding coil