pilot valves are used in compressed air systems to actuate another device using a pneumatic (air) signal. pilot valves always work in conjunction with another device. examples of usage include - actuating a throttle control to slow down or speed up and engine - opening and closing a discharge valve to vent air to the atmosphere - operating intake unloaders in the compressors head. Pilot valves operate in a set pressure range. The range has an unload setting and a load setting. As a compressor operates in this range, it is said to by cycling. At the unload setting, the pilot valve opens and actuates another device (throttle control, discharge valve). At the load setting, the pilot valve closes and returns the compressor to normal operation.