A pressure switch is a form of switch that gives an electrical signal when a certain set pressure has been reached at its input. This is used to provide on/off switching from the pneumatic supply.
The switch may be designed to give a signal either on pressure rise or on pressure fall. This ensures that a component gets either enough pressure or not too much pressure supplied to it, which otherwise could damage the component or stop the component from operating and cause the system to fail.
A regulating screw, which can be adjusted using a small screwdriver, allows the switch to be set to the required pressure.