Relief valves are generally used to protect against high what?

Relief valves are primarily designed to protect against high discharge pressure within a system. Their main function is to prevent pressure buildup that can exceed the safe operating limits of equipment. When the fluid pressure reaches a predetermined level, the relief valve opens, allowing fluid to escape and thereby reducing the pressure in the system to a safe level.

High head pressure refers to the vertical pressure due to the weight of the fluid in a column, and while it can impact systems, relief valves specifically target instances where the discharge pressure, which is the pressure of the fluid leaving a system, becomes dangerously high. This is particularly important in systems like boilers, pipelines, and various industrial applications where excess pressure could lead to catastrophic failures or equipment damage.

The other options do not align with the primary function of relief valves. While they may relate to pressure in specific contexts, they do not reflect the core protection mechanism against high pressure that relief valves are designed for.