A chamber valve, comprising: a frame extending around an elongate portal; a gate operably connected to the frame, wherein the gate is moveable between: a first position in which the gate is offset from the portal, and a second position in which the gate is aligned with the portal; a swing arm extending between the frame and the gate; a first joint at which the swing arm is rotatably connected to the frame; a second joint at which the swing arm is rotatably connected to the gate; and a drive mechanism operably connected to the gate, the drive mechanism configured to cause the gate to move along an arcuate path between the first and second positions, the arcuate path having a radius corresponding to a length of the swing arm between the first and second joints (136, 138); wherein: the gate comprises: a sealing plate having a first major surface facing toward the portal when the gate is in the second position, and an opposite second major surface, and characterised in that the gate further comprises a spring plate parallel to the sealing plate and further from the portal than the sealing plate when the gate is in the second position, and a plurality of rockers, wherein individual rockers of the plurality of rockers are spaced apart along a length of the gate; the drive mechanism is configured to exert force against the gate via the spring plate to move the gate along the arcuate path; the frame includes a stop that resists further movement of the sealing plate along the path while the gate is in the second position; and the plurality of rockers transfers further force exerted against the gate by the drive mechanism to the sealing plate via the spring plate while the gate is in the second position to move the sealing plate toward the portal and away from the spring plate. a frame extending around an elongate portal; a gate operably connected to the frame, wherein the gate is moveable between: a first position in which the gate is offset from the portal, and a second position in which the gate is aligned with the portal; a first position in which the gate is offset from the portal, and a second position in which the gate is aligned with the portal; a swing arm extending between the frame and the gate; a first joint at which the swing arm is rotatably connected to the frame; a second joint at which the swing arm is rotatably connected to the gate; and a drive mechanism operably connected to the gate, the drive mechanism configured to cause the gate to move along an arcuate path between the first and second positions, the arcuate path having a radius corresponding to a length of the swing arm between the first and second joints (136, 138); the gate comprises: a sealing plate having a first major surface facing toward the portal when the gate is in the second position, and an opposite second major surface, and characterised in that the gate further comprises a spring plate parallel to the sealing plate and further from the portal than the sealing plate when the gate is in the second position, and a plurality of rockers, wherein individual rockers of the plurality of rockers are spaced apart along a length of the gate; the drive mechanism is configured to exert force against the gate via the spring plate to move the gate along the arcuate path; the frame includes a stop that resists further movement of the sealing plate along the path while the gate is in the second position; and the plurality of rockers transfers further force exerted against the gate by the drive mechanism to the sealing plate via the spring plate while the gate is in the second position to move the sealing plate toward the portal and away from the spring plate.