Strainers in a hydraulic system can fail and have catastrophic effects on a machine. But why do they fail? A strainer located in the suction port of a pipe is common as is a return to tank side of a circuit. The pressures throughout the circuit will vary and so will the conditions applied to the strainer and its housing. Contamination This is the number one cause of failure irrespective of the location. Whilst a thorough examination of the system may be difficult after such a failure it will pin-point the source of the contamination and lead to a plan to avoid further hydraulic failures throughout the hydraulic system components. Contamination is of course any particle that is not part of the intended hydraulic fluid and its additives. Contaminants throughout the hydraulic equipment must be identified, but these would normally be categorized as :- Solids – Oxidation, Metallic and polymer wear particles Liquids – Water, Fuel, detergents etc Gas – Air Understanding the effect each of these contaminates has on the system components and materials will be essential before a system can be re-commissioned. For example water in a hydraulic fluid can freeze, causing filters to clog with ice and collapse with pressure applied by the hydraulic pumps. Sources of contamination are many and varied, it can be a simple as un-clean oil being used to “top-up” or air bourn dirt drawn in through breather vents. Contamination must be removed before a system is brought back in to service and the best way to do this is to select appropriate filtration. Circulation of the oil with an off-line system will quickly clean the oil within the hydraulic reservoir. Once an oil analysis confirms the oil has been cleaned to a good level, the filters can be serviced. Regular monitoring of the cleanliness will indicate the need for filter changes. If the filters are of the correct design and location they will need changing less regularly. This will then lead to a more efficient and longer lasting hydraulic machine.