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Lubrication Tips for Reliability Professionals

November 1, 2001 Subscribers: 11,549

Book Bits

From the book "Oil Analysis Basics":

How particles affect the oil - Particles, especially catalytic metal particles like copper, iron and lead increase the rate at which oxidation occurs. Particles also strip the oil of its polar additives, including anti-wear additives, extreme pressure additives, rust inhibitors and dispersants. Also, numerous very small particles in stable suspension can cause the oil’s viscosity to increase.

How particles affect the machine - Abrasive particles are responsible for much of the wear leading to premature failure of mechanical components. Under sliding conditions, clearance-sized particles enter the oil film between surfaces and cut away material much like a lathe cuts metal. Under rolling contact conditions, particles transfer concentrated load between two surfaces in relative motion, resulting in surface fatigue, pitting, and spalling. Particle-contaminated oil traveling at high velocity can also cause erosive wear.

Click here for more information about Oil Analysis Basics.

Today's Tip

• When improving fluid cleanliness, it is much easier (and cheaper) to exclude contaminants by ensuring seals, vents and breathers are in good shape rather than to filter out contaminants when they are already inside a component. Use a full flow spin oil filter (with an appropriate beta rating) as an air filter. Because the differential pressure across an air filter is lower than across a full flow oil filter, oil filters are typically more efficient at removing particles from the air than they are from oil.

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Q & A

"We frequently use filter carts as a part of our contamination control program. Do you have any information about how long we should filter the oil using this type of filtration?"

Off-line filtration is a powerful asset to the lube technician. Without interfering with the operation of the equipment, one can keep the oil clean with fulltime offline filtration, or periodically clean the oil with a portable rig, such as a filter cart.

When using a filter cart, the oil is taken from a dirty sump, filtered and returned to the dirty sump. So the cleanliness of the filtered oil is diluted, so to speak, by the dirty oil residing in the tank. To overcome the dilution effect, the tank volume must pass through the filter approximately seven times to achieve the equivalent of single-pass filtration (where the oil is pumped from one container to another through a filter). For example, if you have a 30-gallon tank and a filter cart that pumps at five gpm, you need to run the cart for 42 minutes to equal single-pass filtration (30 gallons X 7, divided by 5 gpm). If you want to achieve two-pass filtration, you must engage the off-line filter for 82 minutes, or about 1.5 hours.

Use this rule of thumb to manage scheduling activities where portable filtration is rotated from machine to machine within the plant.

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