The main difference between pilot operated and direct acting valves is:

The main difference between pilot operated and direct acting valves lies in the method of operation.

Pilot operated valves use a small pilot valve to control a larger flow of fluid, enabling the operation of larger valves with a smaller actuator. The pilot valve directs a small amount of the fluid from the system to control the motion of the larger valve, allowing it to remain more energy-efficient while managing high flow rates. This design allows for the use of smaller actuators and can be more sensitive to control inputs.

On the other hand, direct acting valves rely solely on the actuator's force to open and close the valve. This means that the actuator must be strong enough to directly move the valve mechanism without any assistance from a pilot system. While this can make direct acting valves simpler in operation for smaller applications, they often become impractical for larger valves where increased force is needed.

Thus, the distinction in how the two types of valves operate fundamentally defines their respective functionalities and applications in various systems.