What device is used to activate an inlet air unloader by responding to receiver pressure?

The device used to activate an inlet air unloader by responding to receiver pressure is indeed a spring-loaded pilot valve. This type of valve operates based on changes in pressure within the system, allowing for automatic control of the inlet air unloader.

When the pressure in the receiver reaches a predetermined level, the spring-loaded pilot valve senses this change and opens or closes accordingly. This action directly influences the unloader, which either allows or restricts airflow into the compressor. The design of a spring-loaded pilot valve ensures that it can respond effectively to pressure fluctuations, providing reliable operation for systems such as air compressors.

In contrast, a solenoid valve relies on electrical signals to open or close, making it less suited for direct mechanical response to pressure changes. Springs may be part of a valve mechanism but do not function independently to manage air unloading. A lever, while it can be used in various mechanical roles, does not inherently respond to pressure changes without being part of a more complex device. Thus, the spring-loaded pilot valve is specifically designed for this application, making it the correct choice.