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Throttling Devices or the Expansion Valves Used in the Refrigeration and Air Conditioning Systems

written by: Haresh Khemani • edited by: Lamar Stonecypher • updated: 12/4/2009

This article describes what the throttling valves are, the working of throttling valve, the functions of the throttling valve in the refrigeration and air conditioning systems and the types of throttling valve.

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    Throttling Devices as Important Components of the Refrigeration and Air Conditioning Systems

    Throttling devise is another vital part of all the refrigeration systems and air conditioning systems apart from the compressor, condenser and the evaporator. The refrigerant leaves the compressor at high pressure and temperature and enters the condenser. After leaving the condenser the refrigerant is at medium temperature and high pressure and then it enters the throttling valve. In the throttling valve the pressure and the temperature of the refrigerant is reduced drastically and suddenly. Thus us it is the throttling valve where the temperature of the refrigerant is reduced and it is then able to produce the cooling effect in the evaporator of the refrigerator or the cooling coil of the air conditioner. The throttling valve also controls the amount of the refrigerant that should enter into the evaporator depending on the refrigeration load.

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    What is the Throttling Device or Expansion Valve? How Throttling Devices Work?

    The throttling devise can be the valve or the copper tubing that allows the flow of the refrigerant through very small opening also called as the orifice. The throttling devices allow restricted flow of the refrigerant. The throttling devices are also called as the expansion valves because when the refrigerant passes through them the pressure of the refrigerant drops down or it expands..

    When the refrigerant passes through the orifice its pressure reduces due to friction and also the small opening of the orifice. The amount of the refrigerant flowing through the throttling valve depends on the amount of opening of the orifice. It also depends on the difference of pressure across two sides of the throttling devise that condenser and the evaporator.

    In case of the automatic throttling valve the amount of the opening of the orifice is controlled by the pressure or the temperature in the evaporator. In case of the large refrigeration systems the opening of the orifice is controlled by the level of liquid refrigerant in the condenser or the evaporator. If the throttling valve has fix opening like in capillary tube, the amount of refrigerant flowing through it depends on the pressure towards the inlet side of the throttling valve (condenser pressure) and the outlet side of the throttling valve (evaporator pressure).

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    Functions Performed by the Throttling Devices in Refrigeration Systems

    When the high pressure refrigerant from the condenser enters the throttling devise the pressure of the refrigerant drops down suddenly, due to this the temperature of the refrigerant also drops down suddenly and substantially. There are two important functions performed by the throttling devices or the expansion valves as mentioned below:

    1) Reduce the pressure of the refrigerant: The refrigerant leaving the condenser is at high pressure. The pressure of the refrigerant has to be reduced so that it can vaporize at the required temperature in the evaporator. The small opening or the orifice in the throttling valve reduces the pressure of the refrigerant to the level such that vaporization of the refrigerant occurs. The refrigerant leaving the throttling valve enters the evaporator at low pressure, low temperature and partially liquid and vapor state.

    2) Meet the refrigeration load: The throttling valve also controls the amount of the refrigerant flowing through it and to the evaporator. When there is more refrigeration load that means the quantity of the substance stored in the freezer is more and it is at higher temperature, more amount of heat is to be removed from it. In such cases the throttling devise allows increased flow of the refrigerant through it. When the refrigeration load is less that means the quantity of the substance is less and it is at lower temperature, less amount of heat is to be removed from it. In such cases the throttling valve allows lesser flow of the refrigerant through it.

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    Types of Throttling Devices

    Some of the most commonly used types of throttling valves are:

    1) Capillary tube

    2) Constant pressure or automatic throttling valve

    3) Thermostatic expansion valve

    4) Float valve

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    Throttling Devices for Refrigeration Systems

    Throttling Device in Refrigeration SystemCapillary TubeThermostatic Expansion Valve with CapillaryInternal Parts of Thermostatic Expansion Valve
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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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    Images Courtesy

    1) e-Refrigeration

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
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