Monostable and bistable valves are two types of solenoid valves with different operating principles and characteristics. The main difference between them lies in how they behave when the electrical power supply to the solenoid coil is applied or removed.

1. Monostable Valve:

   • A monostable valve, also known as a normally closed (NC) or normally open (NO) valve, is a type of solenoid valve that requires continuous electrical power to maintain its open or closed state.
   • When the solenoid coil is energized (powered), the valve changes its state (opens or closes) from its default position.
   • When the electrical power supply is removed, the valve returns to its default state due to a spring or other mechanism.
   • Monostable valves are commonly used in applications where the valve needs to be actively controlled, such as in fluid control systems or pneumatic applications.

2. Bistable Valve:

   • A bistable valve is a type of solenoid valve that maintains its open or closed state without continuous electrical power.
   • When the solenoid coil is energized, the valve changes its state and remains in that state even after the electrical power is removed.
   • To change the state of a bistable valve, electrical power must be applied in the opposite polarity to reverse the magnetic field and switch the valve's position.
   • Bistable valves are advantageous in applications where power consumption needs to be minimized or where the valve needs to maintain its position during power loss, such as in battery-operated devices or safety-critical systems.

In summary, the main difference between monostable and bistable valves is in their behavior with respect to electrical power supply. Monostable valves require continuous power to maintain their state, while bistable valves retain their state without continuous power. The choice between monostable and bistable valves depends on factors such as power consumption, application requirements, and system design considerations.