Use and installation of filter drier

The filter drier is a very common accessory in the refrigerant pipeline. It is mainly used to clean up harmful substances in the system, thereby protecting important components such as expansion valves and compressors.

In the refrigerant system, there will be many harmful substances entering the pipeline through various channels, the common ones are the following:

1. Production or maintenance process: At this time, the refrigerant system will be open to the outside world. No matter the length of time, moisture and dust will enter the system pipeline. If there is no nitrogen protection during the welding process, a copper oxygen film may be produced. Even welding slag;

2. Charge refrigerant or refrigerating oil: if these things have many solid impurities and moisture, they will be brought into the system and corrode the metal parts in the system;

3. In the operation of the refrigeration system: In operation, the water in the refrigerant will hydrolyze to form acidic substances, which will corrode the metal. The mixture of refrigerant and lubricating oil can dissolve copper and bring it to the compressor to form a copper film on its metal surface, thereby affecting the compressor's work.

4. Refrigerating oil: when the temperature is low to a certain level, the refrigerating oil will precipitate wormwood, and for the POE oil used as a refrigerant, it has strong hygroscopicity, so it is easier to hydrolyze acidic characteristics.

The existence of the above substances will seriously threaten or destroy the moving parts in the system and the performance of the cylinders and refrigeration systems that require compressed gas, so they must be removed in time.

The main materials in the filter drier are:

1. Metal filter: filter larger solid particles (mainly used in R22 and the use of mineral oil and other small and medium systems that are not sensitive to moisture).

2. Polyester filter: filter tiny particles.

3. Glass wool: filter tiny particles.

4. Molecular sieve: filter large solid impurities, mainly to absorb water, which is 3-4 times that of other substances, and can also absorb nearby acidic substances.

5. Activated alumina: absorbs water, mainly acidic substances.

6. Activated carbon: absorbs paraffin wax, but because the refrigerating oil only precipitates paraffin when the temperature is lower than -35 degrees, it is not necessary to use it in the system running at medium and high temperature.

The purpose of the filter drier is divided into:

Filtering capacity: filter harmful substances in the system, thereby protecting important components such as expansion valves and compressors.

Moisture absorption capacity: It is difficult to determine how much moisture absorption capacity the dryer needs to use for refrigeration products produced according to the standard process. Therefore, the production of general filter dryers is rated according to the requirements of the standard.

Ability to adsorb acid and ester substances: Experiments show that the ability of the filter drier to remove acids and ester substances is directly proportional to the quality of the adsorbed substances, and the external dimensions and outer surface shape have little effect on this ability, except for nothing else. Better industry-accepted methods measure this ability.

Ability to absorb paraffin: For refrigeration systems under low temperature conditions, because the lubricating oil will precipitate paraffin, which will damage the valve parts, it must be removed in time, and activated carbon is often used for adsorption.

Refrigerant flow: because the pressure drop will affect the system capacity too much, so the pressure drop through the filter drier is as small as possible.

Classification of filter driers:

The filter drier for the liquid pipe and the filter drier for the suction pipe can remove substances that may damage the system, but the focus is different.

Dry filter for liquid pipe: It mainly protects valve parts such as stop valve and expansion valve, and avoids clogging of throttling components such as capillary tubes. It is a standard configuration in refrigeration systems. After the liquid line filter drier is usually followed by a liquid indicator.

Suction pipe filter drier: mainly protects the compressor. There are generally two situations in which filter driers for suction pipes are used in the industry.

1. On-site installation system: because the on-site installation is different from the factory, the on-site environment is complicated and the cleanliness is poor, so it is very good to install a filter drier in the suction pipe.

2. Large-scale system: Because the cost of the compressor is relatively high, it is worthwhile to install a detachable filter dryer in the suction pipe to protect the compressor.

In order to ensure that the pressure drop of the suction pipe is as small as possible, the suction pipe filter drier is mainly used when the compressor is burned out, so it can absorb a large amount of water and acidic substances in a short time. Solid impurities, these things will reduce the flow capacity of the filter drier, thereby affecting the performance. If the measured inlet and outlet pressure difference exceeds the lower value, the filter drier must be replaced.

Installation of filter drier:

The filter drier is generally located behind the liquid reservoir in the liquid pipe, but in front of the sight glass, shut-off valve, and thermal expansion valve; there are two types of positions in the suction pipe:

1. Between the gas-liquid separator and the compressor;

2. Between the four-way valve and the gas-liquid separator.

But it should be between the four-way valve and the gas-liquid separator:

1. If impurities enter the suction pipe, it may block the oil return hole filter of the gas-liquid separator, which can be avoided if there is a filter in front;

2. The gas-liquid separator is required to be installed as close as possible to the compressor.

For the drying filter in the liquid pipe of the heat pump system, because of the two-way flow, there are some special installations. In practical applications, there are the following common designs:

1. Only installed on the refrigeration cycle;

2. Use four one-way valves to install the accumulator, filter drier, and expansion valve on the common pipeline, then all of them can be used for cooling and heating;

3. Use two one-way valves and two filter driers to work in the refrigeration and heating cycle respectively;

4. Use a two-way filter drier.

In addition to the drying and filtering work of the normal refrigeration system, the filter drier also has an important function to take on the role of cleaning the system after the compressor is burned out.