The thermostatic expansion valve (TEV), also known as a thermostatic expansion device (TED), is one of the four main components of an industrial or commercial refrigeration system. The other three components are the compressor, evaporator, and condenser. Industrial refrigeration systems usually have multiple evaporators, and each evaporator has a thermostatic expansion valve controlling the refrigerant flow into it.

Some of the major manufacturers of thermostatic expansion valves include Emerson, Danfoss, Parker, Sanhua, Sporlan, and others. Each manufacturer offers a wide range of models designed to work within specific parameters. Therefore, engineers or technicians choose a valve that matches the conditions of the refrigeration system they are designing, modifying, or repairing.

What is a thermostatic expansion valve?

A thermostatic expansion valve is a device that reduces the pressure of the refrigerant liquid it receives from the condenser and then injects and regulates the mass flow of refrigerant entering the evaporator. It performs this regulation based on the temperature of the refrigerant at the outlet of the evaporator. In other words, this device maintains a stable refrigerant temperature at the evaporator outlet by automatically adjusting the refrigerant flow passing through it.

What are the components of a thermostatic expansion valve?

The visible external parts of a thermostatic expansion valve are the body, bulb, and capillary tube. The body is made of brass or stainless steel and has three connections: refrigerant inlet, refrigerant outlet, and equalization port. Additionally, the body contains a regulating screw and a plate-shaped head. The capillary tube extends from the head and has a bulb at its end.

Internally, the TEV has a cylindrical assembly with a calibrated orifice that reduces the pressure of the refrigerant entering the valve. Inside the assembly, there is a screen to retain debris and other impurities.

Furthermore, inside the plate-shaped head, there is a hermetic diaphragm that separates the gas in the bulb and capillary from the system’s refrigerant. The diaphragm transmits its expansion or contraction to a needle, which opens or closes the valve seat. In this way, the thermostatic expansion valve increases or decreases the refrigerant flow exiting the valve.

Thermostatic expansion valves also include a spring, which counteracts the movement of the diaphragm. The force exerted by the spring is adjusted with a calibration screw.

How do thermostatic expansion valves work?

When the refrigeration system is turned on, and the cooling room is at a high temperature, the bulb is at ambient temperature. Therefore, the gas in the bulb is at maximum pressure, fully expanding the internal diaphragm of the valve. In this condition, the force of the diaphragm exceeds that of the spring and the refrigerant pressure. Consequently, the valve opens fully, allowing the maximum refrigerant flow through the evaporator.

As the room and bulb temperature cool down, the gas in the bulb loses pressure, reducing the force on the diaphragm. As a result, the force of the spring and the refrigerant pressure tend to close the TEV, decreasing the refrigerant flow to the evaporator. Eventually, the room temperature stabilizes, and the forces of the diaphragm, spring, and refrigerant reach an equilibrium.

Importance of the thermostatic expansion valve in a refrigeration system

In refrigeration systems, it is generally optimal to maintain a temperature differential of 5°C between the refrigerant inlet and outlet of the evaporators. This ensures high efficiency and guarantees that the refrigerant at the evaporator outlet remains completely in the gaseous state. For this reason, the thermostatic expansion valve is designed, installed, and calibrated to maintain these conditions.

When the temperature differential is below 5°C, there is a risk that a portion of the refrigerant flow remains in liquid form. This situation can cause damage to the compressor, as it is designed to work with gases. On the other hand, if the temperature differential is much higher than 5°C, the refrigerant at the evaporator outlet would be too hot. This can create severe overheating problems in the rest of the refrigeration system (compressor and condenser).

How to select and install a thermostatic expansion valve?

The selection of these valves depends on the manufacturer’s model catalog and the type of refrigerant used in the system. Additionally, factors such as evaporator capacity, refrigerant charge, evaporator temperature, condenser temperature, etc., must be taken into account. Generally, each manufacturer provides software that allows the selection of the most suitable valve for each system.

The valve should be installed as close as possible to the evaporator, using threaded or welded connections. The bulb should be properly positioned directly on the outlet tube of the evaporator and covered with thermal insulation to prevent external interference. If the TEV is installed using welding, it should be covered with a wet cloth to avoid damaging the internal diaphragm. Finally, a refrigerant tap should be installed at the evaporator outlet to measure the refrigerant pressure at the equalization port.

Intersam supplies the refrigeration system your business needs

If you encounter issues with your industrial refrigeration system, it is advisable to seek assistance from a specialized company. At Intersam, we specialize in designing and manufacturing industrial evaporators and condensers.

We design and develop custom refrigeration and air conditioning systems for industrial and commercial applications. Since 1995, we have been manufacturing heat exchangers, refrigeration units, and cooling structures in all their variations: air-to-water, water-to-air, and air-to-refrigerant. All our products feature state-of-the-art technology to ensure optimal performance and maximum energy efficiency.

If your business requires a refrigeration system, contact us. We serve projects in Spain and anywhere in the world.

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