Abstract: A gate valve having a pair of aligned flow passages with a common central axis, with a pair of seat mounts and respective seats facing each other, and forming the walls of a groove with a bottom, their sealing planes tapering toward one another. A riser rises above these seats, with a cap. An actuator rod slides through the cap and mounts and moves an unperforated gate to control flow through the seats. A releasable latch can join the cap and the gate to hold it in its most open position until overcome. A deformable nub is carried by the gate to act as a drag when the gate is moved.