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THIS paper outlines the advantages and disadvantages of present-day hydraulic systems. Included in the discussion are: the blocked return line system for single-acting cylinders, the blocked pump inlet, and the basic open-center-valve system. More advanced designs mentioned are: open-center-valve systems with cylinders in series and with parallel cylinders, close-centered valve systems with pressure regulator, and the central hydraulic and accumulator systems. The author points out that the advantages and disadvantages of each system depend to a great extent upon the design in which it is used.

Multigrade motor oils formulated to meet both Ordnance Supplement 1 and API service “MS” requirements were subjected to over three million miles of heavy-duty field tests. Engine wear and oil consumption were equal to, or lower than, results obtained with single-grade oils in similar service. Trucks, buses, and tractors favor multigrade oils over single-grade oils in engine starting at low temperatures and in fuel economy. Well-formulated multigrade oils also extend the period between engine overhauls and decrease inventory requirements. The savings realized in fuel economy and ease of starting far outweigh the additional cost of multigrade oils. Properly blended multigrade oils give an additional bonus in engine life. These results are dispelling the reservations held by some engine builders and fleet operators concerning multigrade oils.