Control valves are classified based on various factors such as their method of operation, function, construction, and application. Here are some common classifications of control valves:

1. Based on Method of Operation:

   • Manual Valves: These valves are operated manually by a person using a handwheel, lever, or similar mechanism.
   • Automatic Valves: These valves are operated automatically by an external signal or control system, such as pneumatic, hydraulic, or electric actuators.

2. Based on Function:

   • On/Off Valves: Also known as isolation valves, these valves are used to fully open or fully close the flow path.
   • Throttling Valves: These valves are used to regulate the flow rate or pressure within a system by partially opening or closing the valve.

3. Based on Construction:

   • Globe Valves: These valves have a globe-shaped body and linear motion mechanism for opening and closing the flow path.
   • Butterfly Valves: These valves have a disc-shaped closure element that rotates about a central axis to control flow.
   • Ball Valves: These valves have a spherical closure element (ball) that rotates to open or close the flow path.
   • Plug Valves: These valves have a cylindrical or tapered plug that moves linearly to control flow.
   • Diaphragm Valves: These valves use a flexible diaphragm as the closure element, which flexes to control flow.
   • Pinch Valves: These valves use a flexible tube (or sleeve) that is pinched to control flow.

4. Based on Actuation Type:

   • Pneumatic Valves: These valves are actuated using compressed air or gas.
   • Hydraulic Valves: These valves are actuated using hydraulic fluid.
   • Electric Valves: These valves are actuated using electrical power.
   • Manual Valves: These valves are operated manually by hand.

5. Based on Valve Characteristic:

   • Linear Valves: These valves have a linear relationship between the valve position and flow rate.
   • Equal Percentage Valves: These valves provide an equal percentage change in flow rate for a given change in valve position.
   • Quick Opening Valves: These valves provide a large change in flow rate for a small change in valve position at the beginning of the valve stroke.

6. Based on Application:

   • Control Valves: These valves are specifically designed for controlling flow, pressure, or temperature in a process system.
   • Safety Valves: These valves are used to protect equipment or systems from overpressure conditions.
   • Relief Valves: These valves are used to relieve excess pressure from a system to prevent damage or failure.

These classifications help in selecting the appropriate control valve for a given application based on its intended function, operating conditions, and control requirements.