The purpose of a steam trap is to:

The purpose of a steam trap is fundamentally to remove condensate from steam lines without allowing steam to escape. In a steam system, as steam travels through the pipes, it can condense back into water (known as condensate) as it loses heat. This condensate can accumulate and must be removed to maintain the efficiency and effectiveness of the steam system.

If condensate is not effectively removed, it can lead to water hammer, reduced thermal efficiency, and potential damage to the system. A steam trap functions by allowing the water (condensate) to exit while ensuring that the steam continues to move through the system unimpeded. This selective operation is crucial as it supports the system's functionality, stability, and efficiency.

Other options relate to aspects that do not fully capture the steam trap's primary role. For example, while removing steam from a steam line or reducing steam pressure might address certain concerns, they do not accurately define the steam trap's core purpose. Similarly, the collection of steam for storage does not reflect how steam traps are designed to operate in a steam system. Thus, capturing the essence of the steam trap's function is best represented by the need to remove condensate while retaining the steam.