Double isolation and bleed DIB-1 (both seats bi-directional) Double sealing established on each seat bi-directionally by initial plastic-to metal contact in addition to metal-to-metal contact, both upstream, downstream and body cavity. In the closed position, the gate forms a tight seal simultaneously on both seats bi-directionally. This allows the body cavity to be manually bled. An automatic cavity pressure relief device is provided to relieve the build-up of over pressure in the body cavity. Mechanically induced bubble tight seal When closing, the segment is positioned by a mechanical stop while the gate continues going downward, expanding the segment and gate against their opposite seats. This action forms a bubble tight seal on both the upstream and downstream seat to reach a double isolation sealing function. Wear and tear reduction When the valve is completely closed, the gate and segment are wedged tightly against each seat. During operation, the gate and segment retract from the seats prior to stroking; this retraction provides an operating clearance to reduce rubbing of the resilient seat material and protects the sealing surfaces. Additionally this reduces the operating torque and allows a smaller and more economical operator for smooth operation. Lever lock mechanism - Size 150NB (6”) and above The lever arm maintains the gate & segment surfaces parallel by guide plates, while the expanding gate assembly is moving through its stroke. Near the end of stroke, the guide plate allows the lever arm to tilt. The gate and segment slide against their angled faces under stem provided thrust force, creating the expanding seal action. In their final position, the gate and segment are mechanically secured in place. The guide plates forms a rail at both sides of the expanding gate assembly to guide its movements and align it with the seats. Australian Pipeline Valve - Installation, Operation and Maintenance Manual 26 API6D THROUGH CONDUIT EXPANDING GATE VALVE - AP400-405 SERIES In the fully closed position, the segment is positioned by the mechanical stop and the gate is wedged downward under stem thrust force, expanding the segment and gate to form a tight seal on each seat bi-directionally between upstream and downstream. During travel between fully open or close position, the gate and segment retract from the seats prior to travel; this retraction provides an operating clearance to reduce wear on the sealing surface and operating torque. When the bore of the segment is aligned with the body bore, the segment is positioned by the mechanical stop and the gate continues to move upwards, expanding the gate and the segment to form a through conduit bore and protect the sealing surface from flow erosion.