Why are 2-way Vs.3-way Valves Necessary?

In this blog post, you’ll read:If you're an HVAC technician or interested in HVAC controls, valves are important in many processes. But what do all these terms like 2-way vs 3-way valves, mixing, diverting, normally open, and normally closed mean? By the end of this article, you'll have a good grasp of these concepts.
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What do You need to Know about 2-Way vs 3-Way Valves? Give your valve-wielding hero a chance to shine. Get ready as we will reveal the secrets and techniques of 2-way valves vs. 3-way valves! Have you ever tried to decide which valve to pick from the sea of valves inside the hardware store? It’s no longer just you.

Now you don’t have to worry anymore, plumbing heroes! 2 way vs. 3-way valves are not at war with each other on a zero-sum basis. Both are vital in controlling the water flow in your home. To pick the proper valve for every plumbing quest, let’s examine the superpowers of each valve before you get swept away in the current!

If you’re an HVAC technician or interested in HVAC controls, valves are important in many processes. But what do all these terms like 2-way vs 3-way valves, mixing, diverting, normally open, and normally closed mean?

What is a 2-way valve?

2-way valves vs 3-way valves often have “A,” “B,” and “AB” markings on their intake and output ports. Different systems use these valves. You can use them for basic on/off tasks. You can also use them for more difficult tasks involving pumps and variable frequency drives (VFDs).

2 way ball valve
2-way ball valve

How Does a 2-way valve Work?

Imagine a valve with an adjustable stem. The valve opens when you raise the stem and closes when you lower it. The flow usually goes straight through, often to a coil in an air-handling unit.

Types of Control for 2-Way Valves

These valves can be just on/off, or they can help control the flow.

Normally Open or Normally Closed?

In the 2-way ball valve world, you’ll often hear “NO” for Normally Open and “NC” for Normally Closed. These terms tell you the valve’s default state when there’s no power.

For example, in heating systems, people often set valves to fail normally open to prevent coils from freezing. Want to know more about control signals?

open and closed valve
open and closed valve

Different control signals, from hauling off to modulating to pulse width modulation

Pulse Width Modulation (PWM)

Pulse width modulation (PWM) is a powerful digital technique that controls analog circuits through microprocessors’ digital outputs. It finds extensive measurement, communications, power control, and conversion applications.

Digital Control

Digital control of analog circuits offers cost and power savings. Microcontrollers and DSPs often include PWM controllers, reducing power consumption and costs. Digital control eliminates drift, making it ideal for precise

2 way electric valve
2-way electric valve

PWM Controllers

Many microcontrollers include PWM controllers that allow users to set the period, on-time, and direction of PWM output. Enabling the PWM controller initiates the modulation.

Benefits of PWM

  •  Digital vs. Analog:

PWM keeps the signal digital, minimizing noise effects and simplifying communication.

  • Noise Immunity: 

PWM enhances noise immunity, allowing more extended communication channels.

  • Applications: 

Various systems use PWM, including brake control, to offer precise pressure control for optimal performance.

Understanding Three-Way Valves

What is a Three-Way Valve?

A 3 three way ball valve has three ports: “A,” “B,” and “AB.” Port “AB” can connect to either port “A” or “B.” These valves usually appear in systems where the flow is constant and can be mixing or diverting valves.

Mixing vs. Diverting 3-way valve:

A mixing valve has two inputs from the supply side and one output to the return side. It blends the two inputs before sending it out. On the other hand, a diverting valve has one input and two outputs. It channels the flow to one of the two return pipes.

mixing vs. diverting in 3 way valves
mixing vs. diverting in 3-way valves

What is a Diverting Valve?

This is another type of three way diverter valve that redirects the fluid flow between multiple paths.

A diverting valve, often known as a “three-way valve,” is an essential component of any HVAC system. These valves allow fluid distribution from the same source to two separate exits.

Let’s Unpack How It Works.

Anyone may utilize a diverting valve; expertise or training are not prerequisites. The provided valve body has one intake and two different exits. The valve’s internal mechanism can change to discharge fluid through either port singly or together. This function allows you to control the airflow and temperature in a room.

Quick Tips

  • Usually, mixing valves cost less, and you can place them on the return side to save costs.
  • Globe valves and ball valves have different applications. For example, you might use a characterized ball valve for a fan coil unit.
Manual three way ball valve on pipe of industrial boiler heating system
manual three-way ball valve on the pipe of the industrial boiler heating system

The Valve-Powered Wonders of HVAC:

In many HVAC systems, the valve body of 3-way valves is designed to mix fluids, offering variable flow control. While 2-way valves are commonly used for basic operations, globe valves excel in mixing applications, and diverting valves work best when you need to route fluids in different directions.

Diverting valves serve several functions in HVAC systems, including:

Temperature Control:

Hydronic heating systems use diverting valves to mix hot and cold water to reach the desired supply temperature. It maintains a steady and comfortable temperature inside.


In multi-zone HVAC systems, valves control the flow of conditioned water or air to specific areas in a building. This zoning capability may help save energy and accommodate people’s unique preferences for indoor climates.

Chilled Beams:

A common way to control chilled water flow in a business HVAC system is diverting valves.

Energy Efficiency:

Using a diverting valve to control the flow of hot and cold water may increase efficiency and cut costs.

Zonal Comfort:

They enable precise temperature control in different zones, ensuring occupants are comfortable throughout the building.

System Flexibility: 

Diverting valves provide flexibility in system design, making it easier to adapt to changing requirements or expansions.


Suitable diverting valves last a long time and are reliable, which helps HVAC systems work well.

hvac systems work
HVAC systems work

Differentiating 2-way vs 3-way valves

  • 1.    Flow and Pressure Requirements
  • 2.    Pressure and Actuation Response
  • 3.    Integration with Hydraulic System Components
  • 4.    Ergonomic Valve Configurations
  • 5.    Maintenance and Replacement Requirements
  • 6.    Temperature Resistance


In conclusion, choosing between 2-way vs 3-way valves is essential for fluid control systems. 2-way valves are versatile, serving well in on/off and variable flow scenarios. On the other hand, 3-way valves offer advanced fluid control, whether it’s diverting flow or mixing.

For precise temperature regulation, mixing valves are invaluable, while diverting valves manage flow redirection. The choice between 3-way vs 2-way valves depends on the application’s specific needs. 3-way valves offer better control, especially in HVAC and industrial settings. Have you got more questions?

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