Working Process And Applications of Bag-Type Air Filters

The working principle of bag-type air filters is mainly to filter fluids using filter bags, so as to achieve the purpose of fluid purification. Specifically, a bag-type filter consists of key components including a filter housing, filter bags, inlet and outlet pipelines, and support baskets.

Below is a detailed explanation of bag-type (fabric bag-type) air filters.

Installation of Filter Bags for Bag-Type Air Filters

Filter bags are usually made of porous and loose filter materials, such as polypropylene, nylon, polyester, and PTFE. The pore size determines the filtration precision. The filter bags are fixed inside metal or plastic support baskets (also known as mesh baskets) to form a stable filtration unit. The structural design of the support basket ensures that the filter bags maintain their shape under fluid pressure, preventing them from collapsing or rupturing due to pressure.

Fluid Inflow of Bag-Type Air Filters

The fluid to be filtered enters the bag-type filter through the liquid inlet. The liquid inlet is usually located on the side or top of the filter to ensure that the fluid is evenly distributed above the filter bags.

Filtration Process of Bag-Type Air Filters

Under pressure, the fluid passes through the filter bags either from top to bottom or from outside to inside. The microporous structure of the filter bags traps impurities in the fluid, such as solid particles, suspended solids, and microorganisms. Impurities larger than the pore size of the filter bags are retained on the surface and inside of the bags, forming a filter cake layer. Meanwhile, smaller particles may also be captured due to Brownian motion, electrostatic adsorption, van der Waals forces, and other effects. The purified fluid passes through the pores of the filter bags, collects along the designed path (e.g., the wall of the support basket), and flows out from the liquid outlet at the bottom or side of the filter.

Pressure Difference Monitoring of Bag-Type Air Filters

As the filtration process continues, impurities accumulating on the surface and inside of the filter bags gradually increase, leading to higher filtration resistance and a corresponding rise in the pressure difference between the inlet and outlet. When the pressure difference reaches the set threshold, it is usually a signal that the filter bags need to be replaced or cleaned.

Replacement or Cleaning of Filter Bags for Bag-Type Air Filters

When the filter bags become saturated or the pressure difference is too high, they need to be replaced or cleaned. For disposable filter bags or those that are difficult to clean, simply remove the old bags and install new ones. For reusable filter bags that can be cleaned, first close the inlet and outlet valves, release the pressure inside the filter, then open the top cover or quick-opening mechanism of the filter, take out the filter bags for cleaning, and reinstall them after drying. Generally speaking, this type of filter is composed of three parts: a filter cartridge, a filter basket, and filter bags, featuring a compact and simple structure. The fluid to be filtered enters through the filter inlet, flows into the filter bags, and after being filtered by the bags, flows out through the filter outlet. The inlet and outlet of fabric bag filters are generally designed in a side-in and bottom-out mode for easy cleaning.

Main Applications of Bag-Type Air Filters

They are widely used in the filtration of paints, beer, vegetable oil, pharmaceuticals, chemicals, petroleum products, textile chemicals, photosensitive chemicals, electroplating solutions, milk, mineral water, hot solvents, industrial water, syrup, resins, printing inks, industrial wastewater, fruit juice, edible oil, waxes, and other substances.