Filter driers play a vital role in the refrigerant line, primarily to remove harmful substances from the system, thereby protecting vital components such as expansion valves and compressors. In the refrigerant system, various harmful substances may enter the pipeline through different ways, such as the ingress of water vapor and dust during production or maintenance, the influence of solid impurities and moisture when filling refrigerant or refrigeration oil, the acid corrosion when the refrigerant contains water during the operation of the refrigeration system, and the paraffin precipitated by the refrigeration oil at low temperatures. The presence of these substances can seriously threaten or disrupt the performance of moving parts in the system and cylinders and refrigeration systems that require compressed gas, and therefore need to be removed in a timely manner.
The filtration function of the filter drier mainly relies on internal materials such as metal filter, polyester filter, glass wool, molecular sieve, activated alumina and activated carbon. These materials play different roles, such as metal filters and polyester filters mainly filter large and tiny particles, glass wool and molecular sieves absorb moisture and acids, activated alumina absorbs acids, and activated carbon is used to adsorb paraffin.
Depending on the application, filter driers can be divided into two types: filtration capacity and moisture absorption capacity.
In addition, according to the installation location and purpose of use, filter drier can be divided into filter drier for liquid pipe and filter drier for suction tube. The filter drier for liquid pipe is mainly used to protect valves such as shut-off valves and expansion valves to avoid clogging of throttling elements such as capillaries, while the filter drier for suction pipe is mainly used to protect compressors, especially for large systems installed on site, to avoid the problem of high compressor costs.
When installing a filter drier, you need to pay attention to its location. Liquid line filter driers are typically located behind the reservoir and in front of sight glasses, shut-off valves, and thermostatic expansion valves. There are two options for the location of the filter drier for the suction tube: between the gas-liquid separator and the compressor, or between the four-way valve and the gas-liquid separator. For better performance and protection, it is recommended to choose the location between the four-way valve and the gas-liquid separator.
For liquid tube filter driers in heat pump systems, there are some special situations that need to be paid attention to in the installation due to the need for bidirectional flow. In practice, there are several common installation designs, including only installation on the refrigeration cycle, the use of four check valves to set the reservoir, filter drier and expansion valve on the common line, the use of two check valves and two filter driers to work in the refrigeration and heating cycle, and the use of two-way filter driers. In addition, the filter drier functions as a cleaning system, especially after the compressor has burned out.
