Which of the following types of valves is not classified as manual?

A solenoid valve functions primarily as an automatic valve, controlled by an electric current. When an electrical signal is applied, it actuates the solenoid, which opens or closes the valve without manual intervention. This distinguishes it from the other types of valves listed, which are operated manually by a person through mechanisms like levers or handwheels.

In contrast, lever-operated valves, butterfly valves, and gate valves are all types of manual valves. These valves require a physical action from the operator to open or close, making them reliant on human control. This operational distinction underscores the functional difference between solenoid valves and manual valves, highlighting why the solenoid valve is correctly identified as not being classified as a manual valve.