In This Issue:

• Up Front: Grease Gun/Fitting Lesson

• Book Bits: The Risks of Water Contamination

• Today's Tip: Bearing Lubrication Caution

• Q & A: Using a Vacuum to Control Leakage?
  

Up Front

Grease Gun/Fitting Lesson

During my tour with an artillery unit of the Canadian armed forces, we were doing vehicle maintenance when I noticed one of our drivers trying to adjust the track tension on an M-109 self- propelled howitzer.

The tensioner itself was a simple grease fitting that pumped a cylinder and stretched the track. In order to do this, the transmission was required to be in neutral to allow the track-free movement.

This particular driver had not placed the transmission in neutral and was trying his hardest to pump grease into the cylinder with limited success. He had pumped the grease gun so hard that the flexible line had become rigid and he was having trouble removing the hose from the fitting.

In frustration, he flung the grease gun from side to side, causing the grease fitting to break off violently. The grease that was in the track-tensioner discharched with such force that it hit him square in the face and actually pushed the grease into and around the inside of his eye sockets.

He was lucky - doctors at the nearby field hospital were able to scrape and flush the grease out of his eyes without any permanent damage, but it sure scared the grease out of him! (Submitted by Andrew Hirstwood, Ontario Power Generation. Thanks Andrew!)

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Book Bits

The Risks of Water Contamination

From "Filtration Technology":

Combined with a high operating temperature (above 140°F), water reacts with and destroys zinc-type antiwear additives. For example, zinc dithiophosphate (ZDDP) is a boundary lubricant that reduces wear in high-pressure pumps, gears and bearings. When this additive is depleted, abrasive wear accelerates rapidly. This will show up as premature component failures, resulting from metal fatigue and other wear mechanisms.

An inspection of failed components can point to another type of water damage. Aluminum and zinc alloys may have a whitish oxide coating. Bearings and gear surfaces may show signs of pitting. These are signs of corrosion damage. When subjected to water, a bearing will often fail long before reaching its full life expectancy. Besides corrosion, water contributes to shorter component life by lowering viscosity, which reduces the thickness of the fluid's lubricating film. When the film drops below a critical thickness, wear increases rapidly.

More information about "Filtration Technology".

Today's Tip

• It is important that rolling element bearings lubricated by an oil circulation system do not rotate at any time in the dry condition. Especially after a long period when most of the oil will have drained away from the bearing. Rotation under this condition can cause severe damage to the rolling surfaces. This situation may be avoided by ensuring that the oil pump, which supplies the oil to the bearings, is started before the machine drive system is put into operation. (Submitted by Derek Peasley, Application Engineer, FAG Bearings)

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Q & A

Using a Vacuum to Control Leakage?

"We have a critical journal bearing housing with a leakage problem. Because a repair requires a plant shutdown, we have been experimenting with alternatives. Recently we replaced the housing breather with a plant-air Venturi tube, creating a vacuum in the housing that prevents oil leakage. The design has been successful. Can it be considered a permanent solution?"

Theoretically changing air velocity can be used to induce a few inches of vacuum on the housing, and therefore reduce external oil leakage. This should not be considered a viable long-term solution. The pathway by which oil once escaped is now the pathway for external contaminants to enter aided by the internal vacuum.

Best-practice design usually calls for a slight positive pressure on the housing (nitrogen, instrument air or oil mist), or atmospheric pressure with a filter breather - a desiccant- type breather if required. Positive pressure helps to prevent intrusion from contaminants such as particulates and moisture present in the external environment.

The source of the leak should be repaired at the earliest opportunity. If this is a recurring problem, perform root cause analysis to determine why the seals are failing so you can make fundamental corrections.

In the meantime, periodically decontaminate the lubricant with a portable filter cart and monitor particle and moisture levels frequently.

Adam Davis, Technical Consultant, Noria Corporation

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