Unlike spool valves, the functionality of seat valves is based on cones, spheres, or plates that move inside the valve housing and directly seal the inner section. Among their advantages are the quick activation behaviour due to the short distances travelled by the moving parts and limited pressure drop. Seat valves are also hermetically sealed. On the other hand, the control signal must be present throughout the entire process, but a return is only possible by means of a spring. Because the pressure is applied directly to the plate, strong springs are used, necessitating high operating pressure. Seat valve are used primarily in the areas of hydraulics and pneumatics.