What is the operating differential pressure of a relief valve calculated from?

The operating differential pressure of a relief valve is primarily calculated from the cracking pressure. This term refers to the minimum pressure at which the valve begins to open and allow fluid to escape. Understanding the cracking pressure is crucial because it determines the moment the valve will respond to overpressure conditions in the system.

The operation of the relief valve is designed around ensuring safety; once the pressure exceeds this threshold, the valve will vent excess pressure to prevent potential damage or failure in the system. Hence, when focusing on the calculation of operating differential pressure, this pressure point is vital as it initiates the function of the relief mechanism.

Although other pressures, such as maximum pressure, set pressure, or system pressure, play roles in system design and safety considerations, they do not directly relate to the initial opening of the valve - which is crucial for determining the differential pressure effectively. Cracking pressure is the direct measure that indicates when the relief valve starts to perform its primary function, making it the most relevant choice in this context.