The difference between two-way and three-way control valves lies in the number of ports or connections they have and how they are used to control fluid flow within a system. Here's a comparison:

1. Two-Way Control Valve:

   • A two-way control valve, also known as a 2/2-way valve, has two ports: an inlet and an outlet.
   • In a two-way valve, the flow path can be either fully open or fully closed, depending on the position of the valve plug or disc.
   • Two-way valves are typically used for on/off control applications, where the valve is either fully open to allow flow or fully closed to stop flow.
   • Examples of applications include simple shut-off, isolation, or regulation of fluid flow in HVAC systems, water distribution, and process control systems.

2. Three-Way Control Valve:

   • A three-way control valve, also known as a 3/2-way valve, has three ports: an inlet, an outlet, and a common port.
   • In a three-way valve, the common port connects to either the inlet or the outlet, depending on the position of the valve plug or disc.
   • Three-way valves are used for diverting or mixing fluid flow between two different paths or circuits within a system.
   • By adjusting the position of the valve plug or disc, a three-way valve can control the distribution of fluid flow between different process lines, bypass circuits, or heat exchangers.
   • Examples of applications include temperature control in heating and cooling systems, blending of process fluids, and bypass control in pneumatic and hydraulic systems.

In summary, the main difference between two-way and three-way control valves is the number of ports they have and how they are used to control fluid flow. Two-way valves have two ports and are primarily used for on/off control, while three-way valves have three ports and are used for diverting or mixing fluid flow between different paths or circuits within a system. The selection of the appropriate valve depends on the specific requirements of the application, including the desired control function, flow rate, pressure, and fluid characteristics.