Dezincification: Brass is an alloy of copper and zinc, and when exposed to certain environments, such as acidic or high-chloride water, the zinc can be leached out of the brass. This process, known as dezincification, can weaken the brass and cause it to fail.

Corrosion: Although brass is corrosion-resistant, it can still corrode over time, especially when exposed to certain chemicals or environments. This can lead to leaks or failure.

Scaling: Scaling can occur in valves used with hard water, which can lead to blockages and reduced flow rates.

Erosion: High velocity fluids passing through valves can cause erosion, which can damage components and reduce their lifespan.

Mechanical wear: Over time, seals and other components can wear out due to repeated use, which can lead to leaks and reduced performance.

To mitigate these problems, it's important to select the right type of brass for the application, properly maintain and clean the valves, and periodically inspect them for signs of wear or corrosion.