Practical contamination management for hydraulic systems

10 September, 2015

Seven steps

The correct cleanliness level can be established by looking at each of the following seven steps in turn:

• Duty/intended usage.

• Component sensitivity.

• Life expectancy.

• Cost of component replacement.

• Cost of downtime.

• Safety.

• Environmental considerations.

Once each of these is weighted and the required cleanliness level established, an appropriate filtration system can be implemented.

Two main types of filtration system can be specified depending on the needs of the application. A dedicated off-line filtration system operates at a constant flow, maximising filter life and performance, while trolleys can offer a secondary filtration system if connected to the power unit. The likelihood of contaminant introduction can also be reduced by using flat face couplings in conjunction with offline filter trolleys.

Any filtration system is only as good as its filters, which have either a nominal or absolute pore size rating. A nominal rating describes the ability to retain the majority of particulate at the rated pore size, while the absolute rating refers to the filtering media’s capability to retain all particulate of that size. Beta ratios can also be used to determine if a filter is designed for highly efficient removal.

Once installed, the filler breather life indicator must be clearly visible, enabling easy checking for when the unit should be changed. If the unit isn’t changed when indicated, contamination can result – particularly water ingress. Off-line filtration systems should be kept clean, with QRC couplings wiped with a clean, lint-free cloth before connection to minimise the risk of contamination between QRC faces.

To assist in contamination prevention, oil drums should be stored in clean conditions and clearly labelled stating whether they contain clean or dirty oil and what type of oil is contained. Drum tops should always be kept clean. Taps should be fitted correctly, with the tap at the bottom of the drum pointing downwards. The bung should be slightly unscrewed when filling from the drum and immediately tightened to prevent contaminants entering.

When topping up hydraulic power units, the suction pipe should be wiped with a clean, lint-free cloth before lowering into the drum. Spare parts should always be stored in a clean, dry, dust-free environment, with packaging checked to ensure it is intact to prevent contaminant ingress.

Each filter trolley should be clearly marked stating which fluid or oil type it is suitable for, while dust caps should be fitted in all ports of hydraulic cylinders and valves. Any filters which appear damaged should be replaced.

Regular sampling

Once the management system is established, regular sampling should be undertaken to establish any changes in the fluid’s physical or chemical properties and excessive water or particulate contamination. The latter will indicate that the filters are not keeping the system clean, either because they are not suitable for the task, not maintained properly, or the system is subject to excessive ongoing corrosion and wear. Samples should be taken at least monthly.

Contamination management is just one aspect of best practice in hydraulic system maintenance and should be combined with other functions including hydraulic hose inspection and power unit temperature testing as part of a complete maintenance regime.

A specialist maintenance, repair and overhaul (MRO) service provider can advise on implementing complete hydraulic systems maintenance regimes and provide all necessary consumables.

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