Seven steps to hydraulic cleanliness

01 December, 2015

1. Establish component sensitivity

The ISO code of a hydraulic system should always be based on the most sensitive component – that is, the one with the smallest clearance levels. Often a central reservoir will supply a number of systems and in this case either the whole system must be maintained at the cleanliness required of the most sensitive component, or an internal filter must be put in place to protect that component by cleaning fluid before it is reached. Piston pumps are among the most sensitive, while gear pumps and manual valves can be considered the least sensitive.

2. Gauge operating pressure and duty cycles

Normal operating pressure should be taken into account alongside its severity of change. A light duty cycle would see a system operating at its rated pressure or lower for continuous periods with minimal fluctuation – typically at 150 bar or below. Other systems operate with medium pressure changes up to the rated pressure, while heavy or severe duty cycles would experience frequent changes from zero to full pressure and would operate at 300+ bar with frequent, high-magnitude changes in pressure. The pressure rating will determine the material and strength of filter used, which in turn contributes to oil cleanliness.

3. Look at the life expectancy of the equipment

For equipment which is expected to last for more than 20,000 hours of operation, it is prudent to select a greater level of cleanliness than is perhaps required to derive the true value from the machinery. If equipment is only predicted to last around 1000 hours or less (around 125 days of operation at 8 hours a day), component failure is less costly and the minimum level of cleanliness is more acceptable.

4. Evaluate the cost of component replacement

Similar to the above, the most expensive assets should benefit from higher levels of protection. Large piston pumps or high-speed low-torque motors are among the more costly components to replace meaning failure due to oil contamination cannot be countenanced. However, as line mounted valves or gear pumps come at a much lower cost, again the minimum cleanliness level can be set.

5. Calculate the cost of downtime

Realistically, the operational economic liability of downtime must come into play too for similar reasons to the above. Where production is 24/7 any downtime of equipment can be catastrophic, and equally some non-production equipment may be critical especially in temperature-controlled environments. Conversely, equipment which would not heavily impact on production if taken out of action would have a much lower liability due to downtime being less costly. Seasonal production schedules, particularly in the FMCG sector, may also need to be accounted for as downtime is likely to be more costly in peak periods.

6. Assess safety aspects

Components critical to safety must use a more strict cleanliness rating than standard