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Working Of Thermostatic Expansion Valve

Refrigeration is the process of eliminating heat or source of heat from the substance under controlled conditions. The main aim of refrigeration system is to reduce the temperature of the environment by absorbing heat from its surroundings. Thermostatic Expansion valve is a component of refrigeration system which helps in the refrigeration of air conditioning systems. The primary purpose of Thermostatic Expansion Valve is to control the flow of Refrigerant into the condenser which in turn controls the super heating at the outlet at the evaporator.

Thermostatic Expansion valves are also known as metering devices as they are used to measure and control the refrigeration effect in the refrigerating system. These are used primarily for the prevention of flooding of the refrigerant to the compressor to make sure that the machine runs smooth without any fluctuations.

Expansion valve consists of three main parts to regulate the position of the needle that helps in maintaining temperature. A sensor bulb is also provided which monitors and sends the information to be displayed on an output device. A spring helps the thermostatic valve to come in exercise with the refrigeration. The pressure spring can also be set to increase or decrease the desired temperature.

There are two types of TEV (Thermal Expansion Valves)- Internally equalized valves and Externally equalized valves. The only difference between the Internally and Externally equalized valves is the effect of evaporator pressure for the change of position of the needle. Externally equalized valves maintain any difference in pressure through the evaporator unlike Internally equalized thermostatic expansion valves.

Internally equalized thermostatic valves work only on the single circuit evaporators which have very low pressure drops. These cannot handle any high pressure drops or else the system shut downs immediately. The feeder bulb is equipped with liquid refrigerant known as Power Fluid.

Advantages of Thermo-Static Expansion Valves

1. The Thermostatic Expansion Valves controls the flow of refrigerant to the evaporator which helps the plant to               run without any breakdown. So the air conditioning plant can work with optimum efficiency.

  1. It keeps the evaporator completely active which helps in getting the entire work efficiency of the Refrigeration system.
  2. Usually in refrigeration, the entire refrigerant in the evaporator is vaporized which helps prevents the liquid refrigerant from entering the compressor. This helps the Refrigeration system to run freely without any temporary or permanent break down.
  3. The Thermostatic Expansion Valves function according to the given input or desired output. If the load on the refrigerating system is less, low amount of power is consumed and if the load on the refrigerating system is more, high amount of power is consumed. It is a major positive point for the users using Thermostatic Expansion Valve.


It is a control device normally used for controlling the flow of liquid refrigerant. These are used in almost all the commercial and industrial refrigeration systems. Systems with low temperature applications are also capable of using Thermostatic Expansion Valves. The performance characteristics of this Thermostatic Expansion Valves are mostly applicable to any type of refrigeration system which makes it universal to use. The efficiency is very high when compared to other related equipment and is the most widely used valve which shows the adaptive capability of this valve.

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