Bi-directional valves are all-rubber, dome shaped valves that open easier in one direction than the other. The slit on top of the dome opens easily when pressure is applied upon the inside of the dome. Opening in the reverse direction (pressure outside dome) requires buckling of the dome, which requires more pressure. Bi-directional valves can be engineered with two specific opening pressures based on shape/thickness of the dome.
Factors to consider…
- Flow is always more restricted than with duckbill and umbrella valves
- Valve is mounted by the flange the same way a duckbill is mounted
- Often used not as a valve but rather as a catheter seal, sealing around a probe or pipe