How are most hydraulic systems protected against overpressure if pressure control and relief units fail?

The protection of hydraulic systems against overpressure is fundamentally important to ensure safety and reliability. In this case, the most viable method of protection when pressure control and relief units fail involves utilizing a shear section on the main hydraulic pump drive shaft.

The shear section is specifically designed to break when excessive pressure is detected, effectively disconnecting the pump from the hydraulic system. This abrupt disconnection prevents further hydraulic fluid from entering the system and subsequently avoids catastrophic failures that could arise from overpressure, such as component ruptures or structural damages.

While other options may contribute to monitoring or managing hydraulic pressures, they do not provide the same direct mechanical protection against potential system failure due to overpressure. For instance, a pressure gauge allows for monitoring pressure levels but does not prevent overpressure from occurring. Emergency relief valves can help manage pressure but rely on functioning correctly — if they fail, they cannot protect against overpressure. Reducing the fluid supply rate does not directly address the problem of existing pressure but rather manages flow, which may not effectively prevent overpressure scenarios.

Thus, the shear section on the drive shaft serves as a crucial fail-safe mechanism that can avert severe breakdowns in the event of pressure control failures, making it the most effective protective measure in this scenario.