A single pressure control main operates at pressures between 13 and _____ psig.

The main operates at pressures between 13 and 25 psig due to the standard operational range for many pressure control systems. Specifically, a range that includes 25 psig allows for sufficient flexibility in pressure adjustments while also ensuring safety and efficiency in operations. In pressure control systems, maintaining proper pressure levels is crucial for the protection of equipment and the overall system integrity.

Operating within the specified range helps to prevent issues such as over-pressurization, which can lead to equipment failures or risks in the handling of fluids. The choice of 25 psig reflects a common maximum threshold that allows a reasonable margin above the lower limit while still being within acceptable operating parameters for various systems.

Other options represent pressure limits that are either too close together or too high, which would not typically be part of a single pressure control main's operational design.