What is the disadvantage of a direct acting relief valve compared to a pilot operated relief valve?

A direct acting relief valve is designed to open and relieve pressure based on the direct action of the system pressure acting on a spring-loaded mechanism. While this design is straightforward, one significant disadvantage is that the cracking pressure—this is the pressure at which the valve begins to open—can be affected by various factors such as fluctuations in temperature, vibration, and changes in fluid characteristics. This can lead to variability in performance, making the cracking pressure less reliable compared to a pilot-operated relief valve.

In contrast, a pilot-operated relief valve utilizes a pilot system to control when the main valve opens, providing more precise and consistent regulation of pressure. This design helps mitigate some of the variations seen in direct acting valves because the pilot can be tuned to open at a very specific cracking pressure regardless of fluctuations in the system.

The aspects of higher cost, size and weight, and installation complexity do not relate directly to the functionality of the cracking pressure. For example, pilot-operated valves may indeed be more complex and potentially higher in cost and size compared to direct acting valves, but this does not impact the reliability of cracking pressure itself.