An expansion valve reduces pressure in HVAC systems. The two main types are thermostatic expansion valves and capillary tubes. The valve is part of the evaporator and is necessary for the cooling process to work efficiently.
An expansion valve is a piece of equipment that reduces pressure in a system. The most common form of these valves is a thermal expansion valve (TMV), used in heating, ventilation and air conditioning (HVAC) systems. The two main types of expansion valves for air conditioners are thermostatic expansion valves and capillary tubes.
A thermostatic expansion valve controls the flow of refrigerant and can operate at various temperatures or pressures. The capillary tube is responsible for transmitting pressure levels in the system to the sensing tube connected to the TMV and basically acts like a butterfly valve. An air conditioning unit has three main parts: the compressor, the condenser and the evaporator. This valve is part of the evaporator.
To cool a building, refrigerated gas, such as Freon®, passes through the compressor where it becomes hot and pressurized. The gas then flows through coils which dissipate the heat, which condenses it back into a liquid. The condensed liquid then flows through an expansion valve where it evaporates and becomes a cold gas, which extracts heat from the surrounding air. The gas flows through another set of coils and a fan blows cold air into the building and the heat generated in the process is vented outside. A refrigerator or freezer works the same way.
The whole process is done under pressure, which requires the use of a thermostatic expansion valve. When the pressure within the compressor reaches a pre-set level, the TMV opens, allowing the pressure to drop. The Freon® then moves through the valve to the evaporator. This maintains both flow and pressure within the air conditioning system.
The capillary tube contains a filter on one end made of a fine mesh, which prevents debris from entering the tube. It works in much the same way as a thermostatic expansion valve, but it cannot handle significant changes in temperature or pressure. The capillary tube is designed for constant temperature and pressure and works like a butterfly valve between the condenser and the evaporator.
The tubing is typically long and narrow to allow for the Freon® to evaporate as it passes through the tubing. This is necessary to make the Freon® entering the evaporator similar in temperature to that already present in the evaporator. Similar temperatures make the system more efficient and speed up the cooling process.
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