Bidirectional vs Unidirectional Knife Gate Valve
Bidirectional knife gate valves are designed for shutoff with pressure approaching from either side, while unidirectional designs have a preferred pressure direction tied to the seat and body geometry.
Bidirectional capability can change seat construction, body depth, operating thrust and cost, so it should be required only when the process genuinely needs reverse-pressure isolation.
The purchase specification should state normal pressure direction, maximum reverse differential pressure, leakage acceptance and whether dead-end service is required.