Basically both are the Mechanical separation Device which removes or retains the insoluble particles from fluid by employing the porous permeable media. For better understanding it can be classified as under:

Basically both are the Mechanical separation Device which removes or retains the insoluble particles from fluid by employing the porous permeable media. For better understanding it can be classified as under:

• Type of Filter
• Filter Size
• In / Out or End Connection
• Design Pressure (or Working)
• Minimum Design Temperature ( or Working )
• Flow Rate
• Fluid
• Fluid Viscosity
• Degree of Filtration
• Allowable Pressure Drop
• Material Of Construction

1. Filter size: is the pipe line size in which the filter or strainers are connected. Actually it is the inlet and outlet size of the filter.
2. In Out or End connection: is the connection type required to put filter or strainer in the pipe line. This includes inlet and outlet nozzle Flanged type and rating or Threading its Std. or Socket weld / Butt weld Type with its STD.
3. Design Pressure: is the pressure at which filters or the strainers are designed which is higher than the working pressure.
4. Minimum Design Temperature: is the temperature at which the filters or the strainers are designed. This is very important factor to decide the Filter housing, Filter element and the sealing material selection.
5. Flow Rate: is the flow rate of fluid for which the filter or the strainers are designed to give the satisfactory performance.
6. Fluid Viscosity: plays very important role in selecting the filter type and designing the filter element.  
7. Degree of Filtration: is the particle size or the contamination size intended to be removed from the fluid by the strainer or the filter. This may be measured in Micron, Mesh Size, or Millimeter or Thou (thousandth part of a Inch)
8. Max. Allowable Pressure Drop: is the maximum difference in inlet and outlet pressure process can allow. This is due to resistance to flow offered by filter element. This is very important factor in very low pressure filter. Nozzle pipe and Housing also offer resistance to flow which is also added to calculate the Maximum allowable pressure drop.
9. Material of Construction: Is the material which is used to make the filter parts like housing, Filter element, gasket etc.

Mesh size is the no. of opening in one linier Inch on a filter cloth or Mesh. This does not give the absolute size of filtration unless it is described along with the wire size used to make the wire mesh.

For very fine filtration cartridge type filters are more suitable due to their very high dirt holding capacity. Here the fluid is made to pass through the candle having differently arranged multi layers thick filter media.  At different level of depth contaminations ate blocked so it is called the depth filtration. Basket Filters and Bag filters or other type of filter where a single layer of filter media are used are not the depth filter. Wire mesh type basket and Bag filters are not the depth filter media.

All filters or the strainers need cleaning after certain interval of time. For this one has to stop the flow through the filters. When it is not possible to stop the flow through filter one should go for Duplex Filter.

In This Type of Filter the element is cleaned due to rotation of element by scraper blades or a brush the contamination shall be drained down manually or automatically after certain interval of time. This type of filters is available in manual, Semi automatic and fully automatic design.

Generally two Nos. of Three way Ball Valves are used for Duplex Basket Filter up to the available size of 12” NPS. For above size 4 Nos. of Butterfly Valves are used.

When it is required retain ferrous particle a magnetic inserts are installed in the filter housing. Sometimes it is used along with some other type of filter media. Such filters are also called magnetic filter.

The Corrosiveness of the process fluid, Process Temperature and the intended life of the filter are the important factor which governs the selection of material selection. Highly corrosive working condition demands for material with very high corrosion resistance and vice a versa. Also one has to take care for Low or High working Temperature to select the correct MOC. While selecting one has to keep the cost factor in mind to be at optimum level of price and the performance. The main factors the affect the selection are Minimum Design Temperature, Process fluid, and the price.

Papers, Spun Bonded Fibers, Needle Felt, Woven Polypropylene, Woven Cotton, Woven Wire Mesh, Micro Filtration Membrane, Porous Ceramic, Sintered Porous Metal, Five Layer Sintered Wire Mesh, Carbon Bed, Sand Bed, Wedge wire type element are the most commonly used media today.