EXPANSION VALVE AND DRIER
1. Expansion Valve
The expansion valve is a pressure-reducing device that controls the flow of refrigerant from the high-pressure side (condenser) to the low-pressure side (evaporator).
Functions of Expansion Valve:
✔ Reduces the pressure and temperature of the refrigerant.
✔ Regulates refrigerant flow into the evaporator.
✔ Prevents liquid refrigerant from entering the compressor (avoiding damage).
Types of Expansion Valves Used in Refrigeration & Air Conditioning:
(A) Capillary Tube (Fixed Orifice Expansion Device)
- Commonly used in domestic refrigerators and small air conditioners.
- Simple, inexpensive, and maintenance-free.
- A long, thin tube that regulates refrigerant flow based on pressure difference.
- Drawback: Not adjustable; performance depends on refrigerant charge.
(B) Automatic Expansion Valve (AXV)
- Maintains constant pressure in the evaporator.
- Operates based on spring-loaded diaphragm.
- Used in small cooling systems (not widely used in modern units).
(C) Thermostatic Expansion Valve (TXV)
- Most common in air conditioning and commercial refrigeration.
- Uses a thermal bulb to sense refrigerant temperature and adjust flow accordingly.
- Advantage: Efficient under varying load conditions.
- Types:
- Internally equalized TXV
- Externally equalized TXV (better control for large evaporators)
2. Drier (Filter Drier)
A drier is a component used to remove moisture and impurities from the refrigerant.
Functions of a Drier:
✔ Absorbs moisture using desiccants (silica gel or molecular sieves).
✔ Prevents ice formation inside the capillary tube.
✔ Filters dirt, debris, and metal particles from the refrigerant.
✔ Increases efficiency and longevity of the refrigeration system.
Types of Driers:
(A) Solid Core Drier
- Contains solid desiccant material in a compact form.
- Used in small refrigeration units like domestic refrigerators.
(B) Liquid Line Drier
- Installed in the liquid line before the expansion valve.
- Common in air conditioning and commercial refrigeration systems.
(C) Suction Line Drier
- Installed in the suction line to protect the compressor from contaminants.
- Used after system flushing or compressor replacement.
Key Takeaways
✔ Expansion valves regulate refrigerant flow and reduce pressure.
✔ Capillary tubes are simple and widely used in refrigerators.
✔ TXVs provide better efficiency under varying loads.
✔ Driers remove moisture and impurities, protecting the system.
✔ Proper drier replacement prevents system blockages and improves performance.
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