Friction loss in valves depends onCasing materialPipe FlowNominal diameter of the pipeNone of the above

The friction loss in valves depends on several factors. Here's a step-by-step breakdown:

1. Pipe Flow: The rate of flow or the velocity of the fluid in the pipe can affect the friction loss. Higher flow rates can lead to increased friction loss.

2. Nominal Diameter of the Pipe: The size of the pipe also plays a role. A larger pipe diameter can reduce friction loss because it provides a larger area for the fluid to flow through, reducing the fluid's velocity.

3. Casing Material: The material of the pipe can also affect friction loss. Some materials create more friction than others. For example, a rough material like concrete can cause more friction loss than a smooth material like PVC.

So, the answer is not "None of the above". Instead, friction loss in valves depends on the pipe flow, the nominal diameter of the pipe, and the casing material.