Active vs Passive Microvalves and Check Valve

Feature	Active Microvalve	Passive Microvalve
Actuation	Requires external energy/control	Operates mainly due to pressure/flow conditions
Control	Can be actively opened/closed	Opening/closing depends on fluid conditions and geometry
Examples	Piezoelectric, pneumatic, thermal valves	Check, flap, ball valves
Complexity	Generally higher	Generally simpler

Check valve working

A check valve permits fluid flow primarily in one direction and prevents reverse flow.

Simplified diagram:
Inlet → [Valve seat / movable flap] → Outlet

When inlet pressure exceeds the valve opening pressure, the movable element lifts away from the seat and fluid flows forward. When pressure reverses or falls, the element returns to the seat and blocks reverse flow.

Advantages

• Prevents backflow.
• Simple construction.
• Useful for directional fluid control in micropumps and microfluidic circuits.