What does a check valve in the discharge line prevent with a rotary compressor?

A check valve is installed in the discharge line of a rotary compressor primarily to prevent gas from leaking back into the compressor once it has been compressed and discharged into the system. This function is crucial because, without a check valve, the high-pressure discharge gas could flow backward, which could lead to inefficiencies in the system, potential damage to the compressor, and an inability to maintain the necessary operating pressures.

When the compressor operates, it compresses refrigerant gas and pushes it out through the discharge line. If this compressed gas were allowed to flow back into the compressor during its off cycle or low-pressure recovery period, it would interfere with the compressor's performance and reliability. Therefore, the check valve's design allows flow in one direction – from the compressor to the system – while blocking any reverse flow, ensuring that the system maintains its intended pressure and efficiency.

In contrast, other options address different issues not directly related to the primary function of a check valve in the discharge line. For instance, while preventing air from entering the compressor and managing liquid are important considerations in various contexts, they do not fall within the specific role of the check valve in this scenario.