The Helix Knife Valve (also known as a gate valve or a slide valve) is
linear motion valve that has a flat closure element that slides into the
flow stream to provide shut-off. Knife valves are
designed to minimize pressure drop across the valve in the fully opened
position and stop the flow of fluid completely. The direction of the fluid flow does not change, and the diameter through
which the process fluid passes is essentially equal to that of the pipe.
Hence, they tend to have minimal pressure drop when opened fully.