A survey was made in which 144 hydraulic systems were sampled and checked for particulate contamination. The resulting data showed the condition of the hydraulic fluid and permited evaluation of various types of filters, maintenance practices, and system design features. The survey indicated that wirecloth filters fall short of the optimum, and that the older paper filters, when used within their design limitations, give better results. It was also found that the size and number of filters should be proportional to the maximum system flow as well as to the number of components in the system.
