What device protects the steering pump unit from over pressurization?

The device that protects the steering pump unit from over pressurization is the relief valve. This component is designed to open at a predetermined pressure level to allow excess fluid to escape and return to the reservoir, thereby preventing damage to the pump or other high-pressure components in the hydraulic system. By regulating the pressure within the system, the relief valve ensures that the steering system operates efficiently and safely, maintaining optimal performance without risking structural failure from excessive pressure.

While other devices play important roles in fluid systems, such as a check valve that prevents backflow, a rupture disc that acts as a one-time pressure relief mechanism, and a pressure switch that signals when certain pressure thresholds have been reached, they do not actively regulate pressure like the relief valve does. This is why the relief valve is specifically the correct answer for protecting against over pressurization in the steering pump unit.