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.
Basics of 2-Way Valves
2-way and 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 intricate tasks involving pumps and variable frequency drives (VFDs).
How Does a Two-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 world of 2-way valves, 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?
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 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 applications.
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.
Various systems use PWM, including brake control, to offer precise pressure control for optimal performance.
Understanding Three-Way Valves
What Are 3-Way Valves?
A 3-way 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 either mixing or diverting valves.
Mixing vs. Diverting in 3-Way Valves
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.
What is Diverting Valves:
Diverting valves, another type of 3-way valve, redirect the fluid flow between multiple paths.
Diverting valves guide fluid down one path while blocking the other, unlike mixing valves that blend two streams.
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.
How Does it Work?
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.
- 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.
Applications in HVAC Systems
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:
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.
A common way to control chilled water flow in a business HVAC system is diverting valves.
Using a diverting valve to control the flow of hot and cold water may increase efficiency and cut costs.
They enable precise temperature control in different zones, ensuring occupants are comfortable throughout the building.
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.
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?