Pneumatic selector and limiter relays work on the principle of satisfying a preset ______.

Pneumatic selector and limiter relays are designed to operate based on a specific pressure setting. These relays manage operational conditions by responding to changes in air pressure within a pneumatic system. When the pressure reaches the designated preset level, the relay activates or deactivates, allowing it to control the operations of various components in the system effectively.

This is critical for maintaining appropriate system performance, ensuring that machinery or processes function within safe and efficient pressure ranges. Unlike the other choices, which may pertain to electrical or other types of control systems, pressure settings are the fundamental measurement that pneumatic relays monitor to maintain proper function and response.