Filter overview and selection principles

What is a filter?

Filters are small devices that remove small amounts of solid particles from liquids and protect compressors, pumps, meters and other equipment from working properly .

After the fluid enters the filter cartridge with a certain size filter screen, its impurities are blocked, and the clean filtrate is discharged from the filter outlet. When cleaning is required, as long as the detachable filter cylinder is removed and reloaded after treatment. Therefore, it is extremely convenient to use and maintain. Garbage and debris in the pipeline often cause damage to the equipment, such as scale, rust, compound sealants, welding slag and other solid particles, etc. may enter the pipeline system, in order to prevent the fluid containing dust and particles from adversely affecting the equipment , often using filters in pipelines. To protect the pump from construction debris left in the pipeline, a filter device can be installed upstream of the pump. Filters can filter out solid particles in liquids or gases, protecting equipment from damage and preventing pipeline blockages.

There is a filter screen on the flow surface of the filter. When the liquid passes through, most of the impurities will be blocked by the filter screen.  

Scope of the filter

①The filters listed in the standard are suitable for liquid and gas materials in the production of chemical, petrochemical, light industry, etc., to filter their solid impurities, and are usually installed on the pipelines in front of the population of pumps, compressors or flow meters to protect such equipment or instruments.

②The standard includes two series of metric system and inch system: the metric series is divided into three pressure grades: PN10, PN25, and PN40; the inch series is divided into two pressure grades, Class150 (PN20) and Class300 (PN50). The pointed and flat-topped cone filters in the metric series are available in pressure ratings starting from PN6, i.e. PN6, PN10, PN25.

③The main structural materials of the standard filter are cast iron, carbon steel, low alloy steel and austenitic stainless steel. The working temperature range: cast iron is - 20 ~ 300 ° C, carbon steel - 20 ~ 400 ° C, low alloy steel Steel - 40~400°C, Stainless Steel - 196~400°C.

④ The standard filter uses a 30 mesh/in stainless steel wire mesh as the standard mesh, which can intercept solid particles with a particle size of not less than 614 μm. 

Selection principle

The selection of filters can be selected according to the needs of the technological process and pipeline installation, combined with the comprehensive performance of various types of filters. The selection principles and points of attention are as follows.

①In order to ensure the tightness of the pipe network system, the filter with socket welding and butt welding connection can be selected ; if the convenience of replacement is considered, the filter with threaded connection or flange connection can be selected.

②The body material of the filter should be the same as or equivalent to the connected pipe material.

③ For the working medium with a large amount of solid impurities, a filter with a larger filter area is selected.

④ Generally, the filter whose effective filtering area is more than 3 times of the cross-sectional area of the connected pipeline can be used as a permanent filter; the effective filtering area of the temporary filter is more than twice the cross-sectional area of the pipeline. However, when the solid impurity content in the conveying fluid is not much or there are other measures to make up for it, the requirements can also be appropriately reduced.

⑤ The selection of the mesh number of the filter should be considered to meet the needs of the process, or to protect the mechanical energy of fluid conveying such as pumps and compressors.