When using an audible or ultrasonic grease gun attachment for lubricating motors, be sure that the motor grease fitting tube and grease gun coupler do not touch the rear fan bell section of the motor or the coupling guard at the front of the motor. If there is any touching in these areas (even just the paint), the bearing noise is not likely to be the dominant sound heard or registered on the meter. To get a true reading you may have to snap the coupler to the zerk and pull it away from the contact zone while greasing. A pistol-grip grease gun will make this easier. (Jerry Baker, PdM - Lubrication, Tate & Lyle)

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From the book "Oil Analysis Basics":

The amount of water that a given fluid will absorb depends upon its base stock, viscosity, additive package and temperature. The amount of water that can dissolve in a fluid is termed its saturation level. The saturation level for a hydraulic fluid is 200 to 300 ppm while for a lubricating oil it is around 500 to 600 ppm. Oil is cloudy when it is above its saturation level. The saturation level for a synthetic fluid is generally much higher than for a mineral base fluid.

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Question: Large circulating systems are more suitable for condition-based or scheduled (interval-based) oil changes?

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"We have a series of several identical pumps and only the hot ones are foaming. Why?"

This question was asked during a recent course that I was instructing. Initially, I thought that this is contrary to all logic.

Higher temperatures will typically lower the viscosity of the oil. Normally, a thinner oil will have a lower tendency to foam because air bubbles will rise out of the oil more rapidly (actually less aeration), and foam bubbles will have a thinner oil wall which will break more easily.

Foaming is usually caused by:

• a contaminant in the oil (another oil or additive, water, air borne contaminant, cleaning solution (detergent)

• an oil level that is too high, causing frothing or churning

• an oil level that is too low, causing air to get pulled into the suction tube perhaps from a vortex forming in the reservoir, or the returning oil to the reservoir is splashing onto the surface of the reservoir oil.

• the oil temperature is slightly too low (oil is just at the right viscosity to create foam)

• air entering the oil piping on the suction side (upstream, low pressure side) of the pump

Someone in the group posed the possibility that the oil isn't foaming because it is hot, but perhaps the oil is hot because it is foaming.

Bingo! However, the route cause of foaming was yet to be determined. Consider that the foam is displacing the oil and the equipment (bearings, gear) is being starved of oil and creating the heat.

The root cause of the foam is likely an oil level or contamination issue. Adding more antifoam additive usually does not work, and may make matters worse.

Bob Scott, Noria Corporation

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APRIL 2007

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