We recently got a particle counter to use onsite. We took a sample from the hydraulic system on the secondary arm of our No. 3 paper machine. The filter on this system is 3 microns, so we expected to find that the ISO cleanliness level to be at least 15/13/10.

We were shocked that this system was operating at an ISO 22/20/18 - incredibly dirty for system using a servo-valve. We started by changing the filter, checking that it wasn't in by-pass and looking for areas of ingression. Everything checked-out all right.

After further investigation, we noticed on the schematic of the system that almost all of the flow was circulating between the pump through the tank by the relief valve. The flow needed to feed the cylinder was so low that only a small amount of oil was circulating through the filter.

We installed the filter where all of the flow had to circulate through the filter and instantly the particle count went down to 14/13/11. Having a particle counter onsite was instrumental in discovering this problem.

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From the book "Machinery Oil Analysis":

Most industrial machines utilize filtration or are periodically serviced with filter carts. Changing internal filters almost always causes a significant loss of oil that must be made up. Dilution by new oil artificially lowers test results. This effect is proportional to the amount of oil added in relation to the capacity of the system. Small machines tend to lose a higher proportion of total volume during filter changes than large machines.

In some cases, a developing problem such as abnormal wear can be completely masked by a filter change and top-up. In addition, the new filter may exhibit different characteristics, skewing test results even further. When sampling, top-up and/or filter change occurs at the same point in the maintenance schedule, take the sample first.

More information about "Machinery Oil Analysis"

There is some disagreement among electric motor manufacturers as to the best bearing arrangement for horizontal-type, grease-lubricated, ball bearing motors. There is also disagreement on the best technique for replenishing the grease supply in the bearing cartridge.

If the user of these motors wishes to follow the recommendations of all these manufacturers for their respective motors, he must stock or have available ball bearings in a given size with no shield, single-shield and double-shield. He should also train personnel in the relubrication techniques for each make of motor. The confusion thus created in the minds of maintenance personnel may indeed bring about a less-than-satisfactory method of maintaining expensive, important equipment.

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"We would like to standardize on one brand of oil for all our gearboxes but the manufacturer of our worm gears tells us we shouldn't use the EP (extreme pressure) gear oil we use for our reduction gears for this application. Why can't you use EP oil for worm gears?"

Many EP gear oils contain sulfurous additives. These additives are designed to chemically bond to the metal surface of the gears and other components under boundary lubrication conditions to prevent welding of asperities on the two opposing surfaces. While vital in preventing metal-to-metal contact in boundary lubrication regimes, they can be corrosive under certain conditions, particularly to yellow metals such as copper, brass and bronze that are commonly used in industrial worm gears and other components.

The best approach to selecting the correct product for a given application is to gain a thorough understanding of the gear type, metallurgy and operating conditions of the component and to discuss these points with your lubricant supplier and equipment manufacturer. The correct lubricant can then be selected based on load, speed, operating temperature and additive requirements.

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