What type of valve should be located at a low point between the drain valve and the header in the pipeline?

The correct choice is a ball drip, which is specifically designed to facilitate the drainage of any accumulated water or condensate that may collect in the low point of the pipeline. In fire protection systems, maintaining proper drainage is crucial to prevent water stagnation, which can lead to corrosion or other operational issues. A ball drip allows for easy purging of water from the system, ensuring that the piping remains clear and functional.

In contrast, while a ball valve can control the flow of water, it is not optimized for drainage purposes. A relief valve serves a specific function related to pressure regulation and is not suitable for managing condensation or liquid drainage. A reducing valve is intended to lower the pressure of the water in the system, rather than ensuring proper drainage, which makes it ineffective in this particular application. Therefore, for creating a reliable drainage point in the pipeline, a ball drip is the appropriate choice.