By Robert Johnston
Valley Forge, Pa.
My laboratory is responsible for investigating the causes of all sorts of customer problems, among them , hydraulic system failures. In looking at records from the last ten years, I found twenty i nstances where sand had gotten into a system and caused damage to internal parts. Industries where this occurred included steel foundries, a food manufacturer, a steel rolling mill, a petroleum refinery, a truck engine manufacturer, a lift truck, a slag hauler, a tool manufacturer, and a wheel manufacturer.
When we analyze debris from a system filter and find sand, it is almost always mixed with other particles such as limestone, clay, slag dust, glass, paint chips, and wear metal from internal parts. Sand is harder than steel, and just a few grains can do massive damage to valves, bearings, and other hydraulic system components. Sometimes the debris can be found in a fluid sample, but most of the time the fluid looks perfectly fine, because the particles that caused the damage have already been removed by the filters. For this reason, when a customer reports piston or valve damage, we always try to get the filter that was on the system when the damage occurred, since that is where the evidence can be found.
When rapid filter clogging occurs, outside contamination is almost always the cause. In some cases, we are lucky enough to get damaged pump parts for examination, and this can be useful in tracking down the cause of the problem.
One particular customer produced rolled steel products. They used one of our phosphate ester based fluids in their mold oscillation system, and had experienced a recurring breakdown problem. The previous year, they’d had a similar problem, and their engineer saved a small brass part with black varnish on it. He thought that the present situation might be related, so he sent me the part for analysis. We identified the varnish as degraded (cooked) phosphate ester, mixed with significant amounts of silicon, calcium, and other extraneous elements. They didn’t have a system filter available. However, they had collected some dust from the surface of the machine, and we found elements similar to what was in the varnish. We warned them that our analysis showed that the dust could be related to the varnish on the brass part.
One month later, two damaged pistons arrived. Like the earlier brass part, they had black varnish on their surfaces. When we rinsed the parts with solvent to dissolve the varnish, we were surprised to see that what we had rinsed off looked like hundreds of white crystals. Microscopic examination revealed that they were actually grains of sand, stuck to the surface of the valve. We also found steel and bronze wear metal particles. The system was literally being ground up by the sand and other debris. We informed them that they were getting sand and probably other debris into their system, and that they should locate the source of the ingress. The cooked phosphate ester on the parts was the result, not the cause of the pump breakdown. They were able to track down where and how the sand was getting in, and this took care of the problem.
The unfortunate part of the story happened one month after the resolution. Two system filters were submitted to us just to be sure that the problem had gone away. We checked for sand and debris inside the filters and didn’t find any, so the problem had been solved. However, included with these filters was a report from a contract lab, dated one year earlier. At the bottom of the report, their analyst stated that they had found sand in the samples they tested. Apparently nobody at the steel mill had understood the implications of this statement. If they had, they probably could have avoided a repeat of the massive system damage that they had been dealing with.
Robert Johnston is group leader, Analytical Services for Houghton International, Valley Forge, Pa. Contact Johnston at (610) 666- 4114 or via email at [email protected]