How Does an Expansion Valve Work & What Is Its Structure?
Whether you are an HVAC&R professional, business owner, or wholesaler.
As long as you work with expansion valves, the first thing you should know is how they work and the types of expansion valves.
This guide will help you get an understanding of the Thermostatic/Electronic/Capillary Tube expansion valve Principles, Structure, and Types.
How Does a Thermostatic Expansion Valve(TXV/TEV) Work?
Let’s talk about the structure and components of a thermostatic expansion valve before explaining its working principle and “what is thermostatic expansion valve”.
There is a sensor, sensor filling, a membrane, a valve seat, and a housing in an expansion valve body.
The membrane, valve seat, and housing will be connected. You already know it is located in the middle of a condenser and evaporator where there is high pressure and low pressure on the two different sides.
When the high-pressure warm liquid refrigerant gets into the expansion valve from the condenser, it detects this by the sensor. It creates a pressure drop restricting the flow of refrigerant.
This drop in pressure changes the refrigerant from a high-pressure liquid to a low-pressure liquid-gas mixture, which results in a significant temperature drop in the refrigerant.
This low-pressure, low-temperature liquid-gas mixture then enters the evaporator coil. It absorbs heat from the surrounding air, causes it to evaporate, and becomes cold low-pressure gas.
This cold low-pressure gas then gets back to the compressor to complete the cooling cycle.
How Does an Electronic Expansion Valve (EEV or EXV) Work?
Compared with the thermostatic expansion valve, the electronic expansion valve has no damaged accessories and is completely controlled by electromagnetism.
The air conditioner mainboard gives an electrical signal to the electronic expansion valve, and it will perform naming.
It has no temperature transmission from mechanical parts, and all induction comes from sensors.
Therefore, its control has no delay, which is why the control of the electronic expansion valve is more precise.
But the electronic expansion valve has a higher price.
You can better understand how the Electronic expansion valve works in the video.
How Does a Capillary Tube Expansion Valve Work?
You might wonder how the capillary tube expansion valve in HVAC&R works as it doesn’t have any moving parts and is very simple and small in size.
Surprisingly, it is the simplest and most cost-effective expansion valve out there, consisting of a small-diameter capillary tube.
This wound-up copper tube is designed to receive hot, high-pressure liquid refrigerant from the condenser.
But how does it maintain high pressure on one side and low pressure on the other side of the tube? The answer is the friction with the tube’s walls.
This friction plays an important role in rapidly reducing the pressure of the flowing refrigerant.
In a capillary tube, the refrigerant flow is restricted by the tube’s size.
If you compare a capillary tube expansion valve with a thermostatic expansion valve, it is the most durable and cost-effective option because of its small size, simple design, and lack of moving parts.
It became a preferred choice for units produced in large quantities, such as small domestic refrigeration systems and room or window air conditioners.