Hydraulic filters are the mediums in oil Hydraulic system used to arrest impurities and purify the oil to improve the operational efficiency of hydraulic components. 

Need of the Hydraulic filters 

  • The hydraulic oil may contain various contaminates like welding scales, metal chips, tapping compound, sand particles, sludge, rust, water and dirt etc which may result in wear, corrosion, poor performance and ultimately failure of the equipment. 
  • Hence it is necessary to use filters to remove contaminants and supply pure oil to the system. The function of the filter is to separate out contaminants from the oil and clean it. 

Principle of filter 

  • Oil filter is a hydraulic element which removes impurities from the oil and supply clean oil to the system. 
  • Most of the filters work on the principle of trapping the particles in small holes. The fluid may pass through filter element and particles above a certain size become trapped. 

Classification of filters 

Oil filters are classified on the basis of –

A) According to construction of filter medium 
1) Surface filter 
  • It is a thin screen of filter material. 
  • Surface filters are normally constricted from thin sheets of material folded in many sections and turned into multipointed star shape. 
  • There is a large surface area available in a small space. The filter is fitted inside a bowl. 
  • The thin sheets full of holes traps the solid particles as the oil passes through them. 
  • The material used for surface filters are cellulose, woven, steel fibers etc. 
Hydraulic filter


2) Depth filter 
  • It is a thick layer of material. 
  • Depth filters are constructed with a thick layer of material with small passages through which the fluid must pass. 
  • The passages may be formed from granules compacted into thick cylindrical layer compacted into a tube. 
  • The particles become trapped in the passages and oil is filtered out. 
  • The capacity of depth filter is more than the surface filter as well as it also arrest finer materials which can not separated by surface filters. 
  • The filter materials used in depth filter are cellulose, synthetic fiber, metal fibers, glass fiber etc. 


B) According to quantity of oil to be filtered 
1) Full flow filter
  • The entire oil flow is filtered. 
  • Full flow filter is used to filter out the entire flow of oil from inlet to the outlet of filter. 
  • Full flow filter consists of thick depth filter element formed into cylindrical shape and it is placed in a bowl. 
  • The filter has inlet for impure oil and outlet for clean oil. 




2) By pass filter
  • Only a portion of oil is filtered. 
  • When only a portion of the oil is passed through the filter element and main portion of oil is directly passed without filteration. It is called as by pass filter. 
  • In this filter, due to pressure difference between the inlet and restricted passage, a portion of oil is drawn towards the filter cartridge for removing contaminations. 
  • In this fig. the valve opens to bypass the large quantity of oil and only small portions is allowed for filtrations. 


By Aditya

Hi, I’m Aditya Sharma, a professional blogger from Gurgaon, India and I launched this blog called aadityacademy on July 2021. is a mechanical Project-oriented platform run by Aditya sharma and I got the motivation to start aadityacademy blog after seeing less technical education information available on google.

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