How to Working ? The principle of expansion valve and system debugging operation -Professional Freezer Room,Cold Rooms factory

Thermal expansion valve is mainly composed of sensing mechanism, executing mechanism, adjusting mechanism and valve body. When the temperature of the bulb decreases, P1 < P2+F, the valve opening decreases and the refrigerant flow decreases proportionally. When the temperature of the bulb rises, P1 > P2+F, the valve opening increases and the refrigerant flow increases proportionally.Thermal expansion valve is an important automatic control component of refrigeration system, which is divided into external balance type and internal balance type according to different balance modes. It is generally installed between the liquid storage tank and the evaporator. It uses the temperature change of the temperature sensing bulb as a signal to adjust the opening of the valve and change the refrigerant flow, so that the medium-temperature and high-pressure refrigerant can be throttled into low-temperature and low-pressure wet steam, and then the refrigerant absorbs heat in the evaporator to achieve refrigeration effect.

1, The role of thermal expansion valve

Throttling and depressurizing

Throttling and depressurizing the high-temperature and high-pressure refrigerant condensed by the condenser to become a low-temperature and low-pressure vapor-liquid mixture which is easy to evaporate, and enters the evaporator for evaporation to absorb external heat;

Regulated discharge

According to the temperature signal obtained by the temperature sensor, the thermal expansion valve can automatically adjust the refrigerant flow into the evaporator to meet the needs of the changing refrigeration load;

Maintain a certain degree of overheating, prevent liquid hammer and abnormal overheating.

The thermal expansion valve makes the evaporator have a certain degree of superheat by adjusting the flow rate, which ensures the effective utilization of the total volume of the evaporator and avoids the liquid hammer caused by the liquid refrigerant entering the compressor; At the same time, the superheat can be controlled within a certain range to prevent abnormal overheating.

2. Composition and working principle of thermal expansion valve

F: The spring force acts under the diaphragm.

P2: Evaporation pressure acts below the membrane.

P1: The pressure generated by the filling medium in the temperature sensing package acts on the top of the diaphragm.

3, Thermal expansion valve superheat

Usually, thermal expansion has been matched and debugged after leaving the factory, that is, thermal expansion can run stably and produce the maximum energy at the same time. In order to ensure that the thermal expansion valve works at the best matching debugging point, it is necessary to ensure the proper superheat of the thermal expansion valve. The sum of static assembly superheat and effective superheat of thermal expansion valve is called working superheat, which is usually called superheat, and the superheat is 5~8℃.

Therefore, only when the superheat is within this value can the expansion valve reach the maximum cooling capacity without causing wet stroke. Generally, the superheat is required to be between 5℃ and 8℃. If it is found that the superheat is not within this range, it should be adjusted.

For the refrigeration equipment that has just been put into operation, the thermal expansion valve does not need to be adjusted, but after several years of continuous use, the opening of the expansion valve is affected due to the wear of the valve needle, impurities in the system, blockage of the valve hole and weakening of the spring elasticity, which makes the expansion valve deviate from its working point, showing that the opening of the expansion valve is too small or too large.

If the valve opening is too small, there will not be enough refrigerant to evaporate in the evaporator, resulting in insufficient refrigeration capacity and reduced refrigeration effect. [Source: Refrigeration Encyclopedia], if the expansion valve is too open, that is, the amount of liquid supplied by the expansion valve to the evaporator is greater than the evaporator load, some refrigerant will not be able to evaporate in the evaporator and enter the compressor together with gaseous refrigerant, causing wet stroke and possibly damaging the compressor.

4. Commissioning of thermal expansion valve

The adjustment of the thermal expansion valve must be carried out under the normal operation of the refrigeration device. If the flow rate is too large, the adjusting screw can be turned clockwise to reduce the flow rate. On the other hand, if you feel that the liquid supply is insufficient, you can turn the adjusting screw counterclockwise to increase the flow.

Due to the thermal inertia of the thermal expansion valve temperature sensing system in practical work, the signal transmission lags behind, so the whole adjustment process must be patient and meticulous, and the number of turns of the adjusting screw should not be too many at a time, and the number of adjustable turns of the pressure bar type is relatively small. Try to adjust it by 1/4 or 1/2 turns each time, and the interval must be more than 15 minutes every time the expansion valve is adjusted. Patiently adjusted for many times until the requirements are met.

5, expansion valve inspection adjustment cycle

It is not troublesome to check the thermal expansion valve regularly, but it is of great significance to the refrigeration effect, service life, energy saving and the safety of refrigeration units.

The inspection and adjustment of thermal expansion valve focuses on the middle and late life of refrigeration equipment. The following is the inspection cycle reference of thermal expansion valve.

The first four years of use	Five to eight years	Nine years later
1 time per year	2 times per year	3 times per year

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How to Working ? The principle of expansion valve and system debugging operation