Which device is used to help direct airflow in screw compressors?

A slide valve is a critical component in screw compressors, primarily used to control the airflow and adjust the compressor’s capacity. It works by altering the internal volume of the compressor, which effectively changes the amount of compressed air that is generated. When the slide valve is positioned to allow more airflow, it increases the compressor's output, while moving it to limit airflow reduces output. This flexibility is vital in applications where demand for compressed air can vary significantly, ensuring both efficiency and responsiveness to system needs.

The other devices mentioned do serve important functions in a compressed air system. A regulator is typically used to maintain a constant output pressure, but it does not directly manage airflow within the compressor itself. A pressure gauge measures the pressure of the system but does not have a role in directing airflow. Lastly, a blowdown valve is used for safety and maintenance by allowing the release of pressure from the system, but it also does not regulate or direct airflow within the compressor. Therefore, the slide valve is clearly the most relevant piece for the specific function of directing airflow in screw compressors.