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Air breather filter in the OIL TANK filler cap
It is a paper made filter cartridge combined with a wire mesh, whose function consists in reducing the risk of OIL CONTAMINATION, protecting the hydraulic system from dirt, sand, dust and metal – or any other type of – particles coming from external environments.
It’s a simple and not costly item, with no special tool requirements for removal or replacement, providing operators with the following advantages, as a medium-long term result:
The Air breather filter is a perfect starting point to introduce an important topic such as the role of AIR.
AIR is both an essential element for the correct functioning of the hydraulic oil in the circuit and a very dangerous factor at the same time, having negative effects on the fluid properties and, in certain cases, even damaging components and causing failures of the hydraulic system.
As a matter of fact, a certain quantity of AIR is always present in hydraulic oil tanks. Such quantity must be calculated and sized, time by time, according to the required oil volume and to the application of the hydraulic system/machine. This must be considered as a significant driver for the selection of the suitable oil tank for any new hydraulic system project.
For a better understanding, it is worth to consider the role of AIR especially in relation with effects generated by the following most common situations:
In hydraulic oil systems, mechanical energy generated by the vehicle engine is converted into hydraulic energy by the pump.
Operating the tipping valve, it is possible to release the converted energy to the (telescopic) cylinder, which- as a consequence - is activated: the hydraulic oil moves therefore from the tank gradually into the (telescopic) cylinder, accompanying its extension and converting again the hydraulic energy into mechanical energy.
THE FILLER CAP IS NOT COMPLETELY SEALED
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AIR CAN GO IN AND OUT THE SYSTEM
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AIR FILTER INSIDE THE FILLER CAP PREVENT FROM OIL CONTAMINATION, BLOCKING DUST AND FOREIGN PARTICLES FROM THE EXTERNAL ENVIRONMENT
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The free space left by the oil in the tank is then occupied by AIR coming from the external environment, entering the oil tank through the filler cap.
During cylinder lowering, the oil comes back to the tank and returns to its original position. At the same time, the AIR also goes back through the tank cap and it is released outside.
In fact, even if it is closed, the filler cap (or tank cap) is never completely sealed: it features small windows on top of side walls, designed on purpose for the passage of the AIR
These repeated movements of fluids (as described above) make the AIR playing a significant role in hydraulic systems: oil high temperatures, reached during daily operations, can be dangerous, damaging most seal compounds and accelerating degradation of the oil.
Thanks to its continuous circulation inside and outside the oil tank, AIR acts like an essential driver for cooling the system down or at least for dissipating heat outside, reducing negative effects on oil properties.
But on the other side, it represents also a serious threat to the quality of the oil, acting both as a direct and indirect contamination agent.
As a principle, we distinguish among SOLID, LIQUID and GASEOUS contamination.
It is well known that on working fields (quarry&construction sites, mining areas, ports,…) the environmental pollution could be very severe. AIR, as a matter of fact, represents a high-risk VEHICLE OF CONTAMINATION, carrying solid particulate inside the hydraulic system such as: dirt, dust, sand, metal or any other type of particles.
As a result of “solid” contamination, you can have scratches or scores on the inner parts of the system and serious bad effects on seals and fittings with cascading detrimental effects in the medium-long term.
Humid air can also increase the presence of water in the fluid. Such a combination of both water and particulate contamination can lead to the formation of insoluble precipitates and viscous sludges which could clog orifices and oil passages.
TIPS FOR OPERATORS
Special care and precautions must be taken, especially during oil filling/topping up operations, regular maintenance activities or when repairing or replacing any part of the system, to minimize the risk of contamination.
During regular daily operations of the hydraulic system, AIR BREATHER FILTER acts like a shield to protect the system from atmospheric particulate. Obviously, it is important to regularly check the conditions of the filter and replace it, once damaged or saturated.
Even if cleaned from other "solid" agents, AIR itself is in any case a DIRECT CONTAMINATION AGENT(gaseous contamination).
As a general rule we have to say that no oil is ideal: any fluid in fact contains a certain percentage of contaminant agents (including air).
In normal conditions a certain air quantity is always dissolved in fluids (approximately 7-9 % in synthetic oils and 8-10 % in mineral oils).
This percentage can increase as a consequence of:
All fluids react with the oxigen in the air or with compounds that contain oxygen, in a different way according to their specific features and physical characteristics.
This process is well-known as OXIDATION and it consists in a series of chemical chain reactions, with formation of acid residues and insoluble precipitates (lacquers, sludge, gums,…), generating a general degradation of the fluid.
As a first negative effect of oxidation, these products could affect the functioning of the system, increasing wear effect on components and reducing general performances of the machine.
In addition, and as a more severe consequence, fluid’s main properties are significantly altered, facilitating a general premature ageing of the hydraulic oil.
Loss of performances can affect almost all fluid’s characteristics:
- thermal stability,
- hydrolytic stability,
- low chemical corrosiveness,
- anti-wear lubricating capacity,
- low tendency to cavitate,
- water rejection,
- constant viscosity.
Last, but not least, an increased grade of oxidation of the fluid, when combined with temperature increase, can result in a further contamination effect, increasing the oxidation itself and the ageing process in a self-propagating, cascading effect.
In general this process can be accelerated when combined with presence of water, high temperatures and metal particles.
Lubricants should be clean and free from contamination.
But the ideal fluid doesn't exist and this theoretical requirement is not achievable in machines and systems neither from an economic nor a technical point of view.
Lubricants in operation are always contaminated, therefore it is important to use all possible measures and care to keep it under control and minimize negative effects.
MAINTENANCE RECOMMENDATION
Replace the filter element (air breather cartridge) twice a year.
Every six months clean the oil return filter cartridge and replace it at least once per year
Check the oil frequently. Smell and colour of the fluid can be very useful indicators of the oil condition.
Replace existing one, with new clean hydraulic oil at least once a year (or whenever it is necessary).
TIP FOR OPERATORS
It is recommended to remove the air breather cartridge during oil filling or topping up operations.
It must be recognised that this is mainly a paper made filter designed and produced for air filtering only. Any contact with hydraulic fluids can damage it.
Other important phenomena connected with air in relation with hydraulic oil, like turbulences and vortex or foaming are connected with oil viscosity and deserve a special dedicated section.
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