1. n. [Production]

A gate valve comprising a separate gate and segment that move without touching the seats as the valve operates the gate and segment. It permits the valve to be opened and closed without wear. In the closed position, the gate and segment are forced against the seats. Continued downward movement of the gate causes the gate and segment to expand against the seats. When the valve reaches its full open position, the gate and segment seal off against the seats while the flow is isolated from the valve body.

See: gate valve,  seat