The improved oil-cooling technology of recent years has resulted in many hydraulic reservoirs being designed to reduce initial cost and take up less space. Many of these reservoirs lack the capacity to properly maintain the condition of the hydraulic fluid. While heat transfer is being accomplished, many designers fail to plan for the difference the smaller reservoir can make in the effects of contamination from both particulate and moisture. Reducing reservoir capacity reduces oil dwell time, reducing time available for particulate settling, and also for water separation from emulsion to become free water, which may be removed through vacuum distillation.
Hydraulic system components, especially servo and other proportional valves, become easily clogged by particulate in diameters as small as 0.03 micron. Small particles also attack cylinder packing, causing external leakage or internal bypass. Also, the filter may clog and go into bypass well before the scheduled element replacement.
For existing undersized reservoirs, the answer in part is improved filtration, along with the revision of reservoir and filter monitoring and maintenance standards.
An off-line kidney loop filtration system may be the best solution, selecting a high-capacity pre-filter of 10 to 20 micron followed by a 0.03-micron coalescing filter. Both should be electronically monitored.