Copper readings can be particularly alarming when increases are in the hundreds of parts per million. However, huge increases are typically insignificant in terms of component wear. Ironically, small subtle increases in copper are of a higher concern and should be examined closely. Copper alloy component wear is generally accompanied by lock-step increases in alloy metals such as lead, tin, aluminum and zinc. The amount of alloy metal present in brass/bronze components is only a small percentage of the total copper content. Changes in these alloys may be only a few parts per million, but should be taken seriously when present with copper increases. (Submitted by Alan Johnson, Caterpillar SOS Services Coordinator, The Halton Co. Thanks Alan!)

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From "The Practical Handbook of Machinery Lubrication"

Changes in flow rates. When hydraulic oil is subjected to high pressure, some compression of the oil occurs at the rate of about 1/2 percent per 1000 PSI. If the oil volume in the connecting line is 100 cubic inches and the pressure is 1000 PSI, the liquid compression can reach .005 X 100 or .5 cubic inch. When a directional control or other valve is opened downstream under these pressure circumstances, the sudden increased flow rate can be dramatic.

This shock flow can be several times pump output, when large bore and/or long stroke cylinders, operating at high pressure, decompress quickly. When pressure line filters are located some distance from the pump outlet or mounted in the return line, these shock flows can cause filter media bunching or total collapse, particularly in a poorly constructed filter.

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