OIL FILTER
- An absolutely clean fluid essential for reliable operation of hydraulic system.
- Now sophisticated machines like CNC/VMC machines use high pressure oil which demands very very clean oil .
- To clean the oil is a main function of oil filtets. Filters are cleaning stations used to arrest the unwanted materials/particles.
- The hydraulic oil is having following general contaminations:
- Particles ( micron size - metallic/fibrous/dirt)
- Water
- Chemical reaction products such as sludge
- Rubber chips or particles of seats/hoses carried by following oil.
- Other fluids.
- Effect of contaminants: hydraulic system are advancely affected by contamination. If we do not use filter then all these contaminants will flow everywhere with oil, and will block or jam the moving parts. This jamming may result in damaging the entire system. Every dirt particles of 20 micron size can arrest or stop the entire hydraulic system.
- Filters can be classified as:
- Full flow filters
- Proportional flow filters
(A) Full flow filters: as shown in figure oil comes into port A passes through filter element and goes out through port B in this filter all flow passes through filter hence is called full flow filter.
(B) Proportiona flow filters:
In this type mean oil flow passes through Venturi, which creates localized low pressure area inside the filter element. We can see that on outside of filter element this is high pressure oil.
due to pressure difference created across filter element proportionate quantity of oil passes through filter element. In this filter the pressure drop across the filter is very low. Hence, is having wide application.
- Filtration materials: Filter material is wire mesh/screen or paper, cotton, celulocel. Following is the list of fabrication materials for filter media used in Hydraulic oil filter.
- Felt
- Paper
- Fabric
- Wire mesh
- Wire cloth
- Glass fibre
- Paper disc
- Phenolic rasin
- Sintered woven wire
- Sintered PTFE
- Membrane filter
- Magnetic filter cloth
- Symbol of filter : The symbol of inter is as shown figure.
- Location of filter: Filter can be located at three suitable locations in Hydraulic circuit.
- Return line filter
- Suction line filter
- Pressure line filter
(A) return line filter:
- This is common location of filter.
- as you can see that oil is supplying to motor through port A motor is rotating. The oil is returning through port B via DC valve through filter F1 . The oil is collected in oil tank.
- B major disadvantage of this location is that, contaminants are removed only after leaving the system.
(B) suction line filter
- Now, in this location we have fixed the filter on suction line of pump. Hence oil will be filtered before entering into the pump. This prevents random entry of large and other contaminants.
(C) Pressure line filter:
- In this arrangement the filter is located after pump or on delivery side of pump. Full pressure is created by pump and this oil is entering into the filter. This arrangement prevents entry of contaminants generated in the pump into components like valves, actuators etc. Since filter is subjected to high pressure oil, its construction must be robust.





