FEATURE MAINTENANCE MANAGEMENT
PRACTICAL CONTAMINATION management for hydraulic systems
Contamination of fluid accounts for 70-80% of premature hydraulic system failure. Iain Hanson of Brammer looks at how this can be minimised through preventative action
I
ntegral to plant and equipment operation, hydraulic system failure can
be catastrophic with contamination of fluid accounting for 70-80%. Preventative action should therefore be a top priority for maintenance engineers to prevent premature component failure, extended downtime and the associate costs. As contamination can increase wear and shorten machinery and lubricant service life, any action to minimise contamination will have positive effects elsewhere in the system. Gaseous contamination can impair the hydraulic medium’s lubricating properties, increasing ‘metal to metal’ contact, creating wear and a likely increase in other contamination types. Air can cause cavitation and impact on
pump performance. Liquid contamination (water) can drastically reduce the lubricating properties of the hydraulic fluid and cause rust. Cross- contamination (for example, mineral oil- based hydraulic fluids are incompatible with water glycol hydraulic fluids and interfere with their anti-wear properties) can result in the ‘varnishing’ of system components. Similarly, mineral oil reacts with fatty acids contained in water glycol products, forming a ‘white soap’ effect which can block filters.
PARTICULATE CONTAMINATION Soft particles including fibres, abrasion particles, rubber and paint are likely to cause only minimal damage. However, hard particles: iron, steel, brass and aluminium and extremely hard particles such as corundum, rust and furnace dross are highly abrasive and can cause significant surface degradation. Particulate contamination can cause spontaneous outages including valve blockages, substantial pump damage and blown seals and gaskets. When contamination occurs there is a
chain reaction of wear. Gaps grow larger, oil leakages increase, component operating efficiency decreases, blockages occur and metering edges are worn away. Many ‘sudden’ failures are actually the result of cumulative damage over time: even soft particulate contamination must be constantly countered. The usual
8 SEPTEMBER 2015 | FACTORY EQUIPMENT
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. Once installed the filler breather life
causes of contamination are avoidable. Using incorrect fluids, inadequate oil drum and container marking, storing oil drums in contaminated environments or using unclean or contaminated containers to transfer oil or an incorrect filter trolley to transfer fluid can all be prevented with simple control measures. In order to determine ‘how clean is
clean?’ ISO 4406:99 has been developed to provide a standard for measuring and reporting particulate contamination in fluids. This is based around the number of particles of three different sizes per unit volume of fluid and helps engineers understand how equipment performs at different cleanliness levels through evaluating the level of contamination protection needed based on operating pressure. The correct level can be established by considering the following: ● 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. 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 be reduced
In order to determine ‘how clean is clean?’ ISO 4406:99 has been developed to provide a standard for measuring and reporting particulate contamination in fluids
indicator must be clearly visible; if it isn’t changed at the right time contamination, water ingress in particular can result. 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. 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 as to which fluid or oil type it is suitable for while dust caps should be fitted in all ports of hydraulic cylinders and valves. Once the management system is established, regular sampling (at least monthly) will 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 because they are not suitable, not maintained properly or the system is subject to excessive ongoing corrosion and wear. Contamination management is just one aspect of best practice in hydraulic system maintenance and should be combined with 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.
Brammer T: 01782 662100
www.brammeruk.com
/ FACTORYEQUIPMENT
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