What mechanism is used to enable the discharge of compressed air into the air receiver?

The discharge of compressed air into the air receiver is facilitated by a spring-loaded valve, which serves as a critical component in managing the flow of air. This type of valve employs a spring to maintain a closed position and only opens when the pressure reaches a predetermined level, allowing the compressed air to flow into the air receiver as needed.

The spring-loaded mechanism ensures that the valve responds to changes in pressure dynamically, providing an operational aspect that allows it to close again once the desired pressure is achieved, preventing over-pressurization. This functionality is essential for the safe and efficient operation of systems that rely on compressed air, ensuring that air is introduced into the receiver reliably and systematically.

In contrast, while an electric motor might be involved in powering compressors that create the air pressure, it does not directly manage the air discharge into the receiver. The intake valve regulates airflow into the compressor, rather than the discharge into the receiver itself. Similarly, a piston mechanism is typically used in compressors to compress air, rather than to release it into a receiver. Therefore, the spring-loaded valve is the correct answer due to its specific role in controlling the discharge of compressed air into the air receiver.