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Thermostatic Expansion Valve or TEV

written by: Haresh Khemani • edited by: Lamar Stonecypher • updated: 2/16/2010

Thermostatic expansion valve is one of the most commonly used throttling devices in the refrigeration and air conditioning systems. Let us see the details of this valve that automatically maintains the flow of the refrigerant inside the evaporator.

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    What is Thermostatic Expansion Valve or TEV?

    Thermostatic expansion valve or TEV is one of the most commonly used throttling devices in the refrigerator and air conditioning systems. The thermostatic expansion valve is the automatic valve that maintains proper flow of the refrigerant in the evaporator as per the load inside the evaporator. If the load inside the evaporator is higher it allows the increase in flow of the refrigerant and when the load reduces it allows the reduction in the flow of the refrigerant. This leads to highly efficient working of the compressor and the whole refrigeration and the air conditioning plant.

    The thermostatic expansion valve also prevents the flooding of the refrigerant to the compressor ensuring that the plant would run safely without any risk of breakage of the compressor due to compression of the liquid. The thermostatic expansion valve does not controls the temperature inside the evaporator and it does not vary the temperature inside the evaporator as its name may suggest.

    Beside the capillary tube, the thermostatic expansion valve is used widely in the refrigeration and air conditioning systems. While the capillary tube is used in the small domestic systems, the thermostatic expansion valve is used in the systems of higher capacities. It is commonly used in the industrial refrigeration plants, high capacity split air conditioners, packaged air conditioners, central air conditioners and many other systems.

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    Thermostatic Expansion Valve or TEV

    Thermostatic Expansion ValveTEV with CapillaryConstructional details of TEVThermostatic Expansion Valve  Application
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    Functions of the Thermostatic Expansion Valve

    The thermostatic expansion valve performs following functions:

    1) Reduce the pressure of the refrigerant: The first and the foremost function of the thermostatic expansion valve is to reduce the pressure of the refrigerant from the condenser pressure to the evaporator pressure. In the condenser the refrigerant is at very high pressure. The thermostatic expansion valve has a constriction or orifice due to which the pressure of the refrigerant passing through it drops down suddenly to the level of the evaporator pressure. Due this the temperature of the refrigerant also drops down suddenly and it produces cooling effect inside the evaporator.

    2) Keep the evaporator active: The thermostatic expansion valve allows the flow of the refrigerant as per the cooling load inside it. At higher load the flow of the refrigerant is increased and at the lower loads the flow is reduced. It won’t happen that the load on the evaporator is high and the flow of the refrigerant is low thereby reducing the capacity of the evaporator. The thermostatic expansion valve allows the evaporator to run as per the requirements and there won’t be any wastage of the capacity of the evaporator. The TEV constantly modulates the flow to maintain the superheat for which it has been adjusted.

    3) Allow the flow of the refrigerant as per the requirements: This is another important function of the thermostatic expansion valve. It allows the flow of the refrigerant to the evaporator as per the load on it. This prevents the flooding of the liquid refrigerant to the compressor and efficient working of the evaporator and the compressor and the whole refrigeration plant.

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    Advantages of the Thermostatic Expansion Valve

    As it is obvious from the above discussion the advantages of the thermostatic expansion valve are:

    1) The TEV maintains the flow of the refrigerant to the evaporator as per the load inside. Thus the refrigeration or the air conditioning plant can run to the optimum capacity as per the requirements.

    2) The TEV keeps the evaporator fully active and helps getting the optimum cooling effect from it.

    3) Since the entire refrigerant in the evaporator gets vaporized the chances of the liquid refrigerant particles going to the compressor are reduced. This reduces the chances of the breakdown of the compressor due to compression of the liquid.

    4) The compressor can also work at the optimum capacity as per the refrigeration load on the system. If the load is lesser it has to compress refrigerant and work on lesser capacity thus absorbing lesser electric power. If the load is higher it can work at higher capacities.

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    Types of Thermostatic Expansion Valves

    There are two types of thermostatic expansion valves:

    1) Internally equalized thermostatic expansion valves

    2) Externally equalized thermostatic expansion valves

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    Reference

    1) Book: Basic Refrigeration and Air Conditioning by P. N. Ananthanarayanan, Second Edition, Tata Mc-Graw-Hill Publishing Company Limited

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Throttling Devices, Expansion Valves in Refrigeration & Air Conditioning Systems

This is the series of articles that describes what the throttling valves are for the refrigeration and air conditioning systems. It also describes the functions of the throttling valves and also its types like capillary tube, automatic expansion valve, thermostatic expansion valve etc.
  1. Throttling Devices or the Expansion Valves Used in the Refrigeration and Air Conditioning Systems
  2. Capillary Tube for Refrigeration and Air Conditioning Systems
  3. Constant Pressure Expansion Valve or Automatic Expansion Valve
  4. Thermostatic Expansion Valve or TEV
  5. Float Valve used as the Throttling Device in Refrigeration Systems