Pocket filters working principle
The working principle of pocket filters differs from the role of a “sieve.” Due to the airborne dust particles, there will be inertial or irregular motion under the action of airflow.
And there is a force called the “van der Waals force” between objects (i.e., molecules and molecules, molecular groups and molecular groups between the adsorption force), which makes the dust particles entering the air filter pocket, the occurrence of adhesion in the air filter pocket fiber surface, to achieve the purification of air.
In addition, the smaller dust particles in the air, only when colliding with each other, will adsorb each other and form larger particles before they sink. Because of motion friction, the fiber filter material and micro-dust may take on an electric charge and produce an electrostatic effect.
Pocket filter material with static electricity after the resistance remains unchanged. It even improves the filtration effect, because static electricity will cause the micro-dust to change the trajectory of movement. When this dust hits the bag filter, the micro-dust in the filter media sticks more firmly to the incoming fine particles.
Pocket filters’ material composition and characteristics
The core filter media of the pocket filter is a new composite non-woven fabric, and every two filter pockets are fixed with metal strips to increase the strength of the filter pockets. So it is also called a rigid pocket filter.
The pocket filter is with a high dust capture rate, low resistance, good air permeability, large dust capacity, good sealing, reliable power, no leakage or not easy to rupture, and other product characteristics.
The filtration efficiency is between 60% and 95% (@1~5um colorimetric method), the applicable temperature is about 80℃, and the relative use humidity is about 80%.
A pocket filter is commonly used in the middle filtration of the air filtration system, and the filtration efficiency is mostly medium-efficiency.
The main products of medium-efficiency air filters are electrostatic cotton bag filters, synthetic material bag filters, deep pleat filters, V-type filters, box filters, pocket glass fiber air filters, and other categories.
Among them, the bag filter is divided into five levels of F5, F6, F7, F8, F9, etc., according to the colorimetric filtration efficiency from low to high between 60% to 95% @ 1 to 5um.
Application of pocket filters
The pocket air filter has a lot of applications in the HVAC system of commercial buildings as a dust collector, it is widely used in airports, office buildings, hotels, cinemas, etc.
In the industrial field, it is mainly used in the engineered filtration systems for the electronic industry, semiconductor, precision manufacturing, photoelectric industry, medical and pharmaceutical, food, and other industries.
For the industrial clean room of medicine, LED/LCD with high clean requirements, the pocket air filter is mainly used for mid-range filtration, as the front-end filtration of high-efficiency filtration, to reduce the load of high-efficiency filtration and extend the service life of HEPA filter or final filters.
Factors affecting the service life of pocket filters
There are two factors affecting the resistance of the filter.
The first is wind speed. The bigger the wind speed, the bigger the resistance of the filter;
The second is the dust concentration—the more serious the pollution, the greater the resistance. In the case of air speed remains unchanged, and the resistance size can reflect the filter’s dust capacity.
When the dust capacity of the filter pocket reaches its rated value, the resistance no longer increases, then its service life is up, and this time it needs to be replaced with a new pocket air filter.
In some special scenarios, such as a paint spraying workshop, because there is a lot of paint mist, the pocket air filter will soon be pasted by the paint mist, thus losing the filtration capacity, and generally need to be replaced in about 7 days.
