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Know-how
Recommended Oil Cleanliness Codes for Components
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The selection of the filtration grade is focused to the given oil cleanliness code in the corresponding hydraulic or lubricating oil system.
By the presetting of this oil cleanliness the machine's component clearance, the dirt sensitivity and the operating method play a major role.
Thus, gear pumps having very small clearances, due to their design form this kind of pump is not very dirt sensitive.
For this reason gear pumps do not demand the use of a 3 micron filter.
The operating method of a system is a further deciding factor by the determination of the filtration grade of the full flow filter. In systems with a high capital expenditure, for example a paper machine which has to reach an maximum availability,
considerably finer filters are used from the outset than in for example, smaller, single, hydraulic presses which may be shut down for the purpose of maintenance or filter change.
The following table shows typical clearances for some important fluid power components.
Hydraulic components and clearances
Gear Pumps
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| Gear-side plate | 0,5...5µm | | Gear-housing | 0,5...5µm |
Vane Pumps
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| Vane tip | 0,5...5µm | | Vane side | 5...13µm |
Piston Pump
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| Piston bore | 5...40µm | | Valve plate -cylinder | 1,5...10µm |
Proportional valve
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| Control piston | 2,5...23µm | | Needle valve | 13...40µm |
Servo valve
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| Control piston | 18...63µm | | Needle valve | 2,5...8µm |
Directional valve
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| Control injector | 130...10.000µm | | Piston-sleeve | 1...23µm |
Pressure valve
Bearings
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| Hydrostatic bearing | 1...35µm | | Roller bearing | 0,5µm | | Friction bearing | 0,5...100µm |
Recommended oil cleanliness codes for fluid power components and applications
Under consideration of the above mentioned criteria and due to experience values following oil cleanliness codes are recommended.
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| Very dirt sensitive systems with high availability. Flushing of very dirt sensitive fluid power systems | better than 13/12/8 | | Dirt sensitive fluid power systems Servo valve technology > 160 bar | better than 15/13/10 | | Fluid power systems with proportional valves operating pressure > 160 bar | better than 17/15/11 | | General machine hydraulics | better than 19/17/13 | | Machine hydraulics and fluid power components with low dirt sensitivity | better than 21/18/14 |
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