A Guide to Thermostatic Expansion Valves


Reaping the most enjoyment from your air conditioning system is easy when you know a bit about how it works. One of the four main components of an air conditioning system is the thermostatic expansion valve, or TXV for short. The other three are the compressor, condenser, and evaporator. Together, they cool your home.

Where the Thermostatic Expansion Valve Is Located

The TXV has a sensing bulb that is located near the output side of the evaporator. The valve itself is located along the line that carries refrigerant. It does not need to be next to the sensing bulb.

What a Thermostatic Expansion Valve Does

The TXV releases the right amount of refrigerant into the evaporator at the right time. When refrigerant is no longer needed, the TXV closes to prevent refrigerant flow.

The Parts of a Thermostatic Expansion Valve

The first important part to mention when talking about the TXV is the sensing bulb. Although it isn’t housed within the valve itself, it’s necessary for the TXV’s function. The sensing bulb is full of refrigerant that responds to pressure changes.

The next part is the capillary tube. This tube is a thin metal pipe that carries refrigerant from the sensing bulb to the TXV. It’s a straight pipe when it emerges from the sensing bulb. As it approaches the TXV, it coils.

The external valve itself consists of a powerhead or cap and two pipes that perpendicularly intersect one another. The inside of the valve contains a diaphragm and a pressure spring.

How Does a Thermostatic Expansion Valve Work?

The sensing bulb gets hot when the evaporator does. As the temperature rises, the pressure of the refrigerant rises as well. When this pressure climbs enough, some refrigerant begins to move down the capillary tube into the valve.

As the cap of the valve fills with refrigerant, it pushes a small piece of sheet metal down. This formal name for this small metallic piece is the diaphragm. As the diaphragm moves down, it opens the valve.

Once the valve opens, the refrigerant begins to flow into the evaporator. Since refrigerant removes heat, the evaporator begins to cool down. Once your air conditioning system reaches the temperature you have selected on your thermostat, the pressure in the sensing bulb decreases, and the refrigerant holding the diaphragm down begins to move back up to its starting position.

There is a pressure spring on the other side of the valve. This pressure spring is adjustable and must be accurately set according to manufacturer specifications. The pressure from this spring and the evaporator combine to counteract the pressure from the diaphragm. This counterpressure is what closes the valve. As the evaporator warms again, the pressure inside of the sensing bulb increases and triggers the start of another cooling cycle.

Why Is a Thermostatic Expansion Valve Important for Your Air Conditioning System?

Since the TXV only allows the proper amount of refrigerant to be released, your air conditioning system only cools at your command. As a result, your system doesn’t have wear and tear from excessive cooling. A TXV also helps prevent excess backflow of refrigerant through the condenser. This prolongs the life of your system.

Getting the most years possible from your system isn’t just great for your wallet. It’s good for the environment. When you can use a system longer, you delay its disposal. If you make excellent air conditioning system maintenance a long-term habit, you will dispose of fewer systems during your lifetime.

Another benefit to the environment is reduced energy use. When your system cools to your desired setting, it doesn’t use any more energy than you decide, and your energy bills are more manageable. As a result, you can make energy consumption decisions that are good for your conscience and wallet.

How You Can Learn More About Your Thermostatic Expansion Valve

Understanding your TXV and other air conditioning system components is crucial to getting the most from your system. You can quickly troubleshoot your system when you know what is expected and what might require a repair call. Another way to enjoy an optimal comfort level within your home is to bring in a trusted team.

We specialize in heating and cooling repair, installation, and maintenance services. We can also improve your home’s indoor air quality. Contact Texas Air Authorities in Arlington, TX, for more information about our comprehensive services.

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