Anatomy of a Grease Gun

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29356/grease-gun-anatomy

While anatomy is commonly associated with biology and medicine, this article does not include the study of the human body. However, the typical illustrative methods used for detailed examination and analysis of bodily features have always been an effective learning tool in the classroom. The anatomy lessons within Machinery Lubrication will apply these same methods for various topics within our industry.

In this issue, the grease gun will be dissected to uncover all of its component characteristics. In addition, several other related topics will be discussed, such as common grease gun disorders, symptoms of incorrect greasing volume or frequency and best practices for using a grease gun.

Types of Grease Guns

Grease guns have three ways in which they can be powered: by hand, air or electricity. Aside from these variations, the hand-powered (or manual) grease guns can either be manufactured with a lever or a pistol grip. The benefits to each of these depend primarily on the intended application and the lubrication technician’s personal preference. One other major variation to the grease gun is how the grease is to be loaded: by suction fill, cartridge or bulk.

Manual (Lever) – This is the most common type of grease gun and can supply around 1.28 grams of grease per pump, which is forced through an aperture from hand pumps.

Manual (Pistol Grip) – This variation of the lever-type grease gun allows for the one-handed pumping method, which is very common. It provides approximately 0.86 grams per pump.

Pneumatic (Pistol Grip) – This grease gun uses compressed air directed into the gun by a hose activating a positive displacement with each trigger.

Battery (Pistol Grip) – This is a low-voltage, battery-powered grease gun that works comparably to the pneumatic grease gun. It offers the advantage of being cordless.

It’s fundamental that grease is used as a lubricant because it clings to a machine’s moving surfaces without easily leaking away like oil. For this reason, the filling and refilling of grease in grease-lubricated machines must be treated differently than that of oil-lubricated machines. Therefore, it is essential that the proper grease gun operation is understood and managed by lubrication technicians for bearing and machine reliability. Simply knowing the signs of overgreasing and undergreasing and how often to reapply can go a long way in extending machinery life.

Connectors, Adapters and Couplers

A grease gun may come with the standard connection adapter such as a hydraulic coupler, but there are several variations depending on the application. The standard hydraulic coupler is the most commonly used and most applicable. A 90-degree adapter is ideal for fittings in confined areas that require a 90-degree bend. A needle-end adapter provides a thin, precise amount of grease for tight places, while a three-jaw swivel coupler offers a variety of locking positions for different applications.

Flexible Hose vs. Fixed Tube

The decision to use a flexible hose or a fixed tube depends on the machine’s grease-fitting type and ease of location, as well as the type of grease gun used. For example, a hard-to-reach location would benefit from a flexible tube. On the other hand, lever-style grease guns require both hands to pump the grease and would favor the fixed-tube alternative.

Accessories

Grease gun meters can be retrofitted onto a grease gun to help optimize lubricant consumption. Plastic caps provide benefits such as preventing corrosion and debris. They also can be color-coded so that cross-contamination does not occur. Other accessories such as sonic/ultrasonic devices are also available.

Grease Fittings

Grease fittings have several names such as a Zerk fitting, grease nipple or Alemite fitting. This is the lubrication point where the grease connector is attached. The standard hydraulic grease fitting is most commonly used for standard applications. It can be either upright or angled. The button-head fitting is ideal for good coupler engagement when large volumes of grease are being added. A flush-type grease fitting is preferred when space is limited for standard protruding fittings, while the pressure-relief vent fitting helps prevent higher pressures that could lead to damaged seals.

Machine Health Risks Associated with Grease Guns

High Grease Gun Pressure

A high-pressure manual grease gun is designed to deliver from 2,000 to 15,000 psi. Applying too much pressure while greasing will damage the bearing seals, which rarely handle more than 500 psi. Symptoms of high grease gun pressure include collapsed bearing shields, damaged bearing seals, grease driven into electric motor windings, and safety and environmental issues.

Regreasing Frequency

Managing regreasing frequencies to optimal conditions is necessary to avoid long-term machine health problems. If the frequency is too long, symptoms may include lubricant starvation, which promotes wear, friction and grease contamination. If the frequency is too short, excessive grease consumption and safety and environmental issues may occur.
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Overgreasing and Undergreasing

It is important to know the exact amount of grease necessary for your greasing application to avoid overgreasing or undergreasing. Symptoms of overgreasing include damaged seals and motor windings, environmental issues, and fluid friction, which leads to increased heat generation, higher grease oxidation rates and higher energy consumption. Symptoms of undergreasing include bearing starvation, which results in friction wear and increased contamination.

How Output is Measured

It is common for maintenance departments to have a wide variety of grease gun types, makes and models. This can cause grease-related disorders due to cross-contamination and inaccurate knowledge of each grease gun’s output per stroke. Grease guns are known to vary in the amount of grease that is output from 0.5 grams to more than 3 grams. This inconsistency depends on factors such as the type, model and age of the grease gun.



To overcome this problem, it is necessary to calculate the amount of grease that is released from a grease gun per stroke. To do this, use a calibrated scale and consistently pull 10 strokes of grease onto the scale. Once this value is known, divide by 10.

Grease Gun Best Practices

• Calculate the proper amount of grease needed for the relubrication of bearings based upon the calibrated delivery volume of the selected grease gun.
• Use a vent plug on the relief port of the bearing to help flush old grease and reduce the risk of too much pressure on the bearing.
• Use extreme caution when loading grease into the grease gun to ensure that contaminants are not introduced. If using a cartridge, be careful when removing the metal lid so that no metal slivers are introduced into the grease.
• Make sure the grease gun is clearly marked to identify the grease with which it should be charged. Do not use any type of grease other than that which is identified.
• Always make sure the dispensing nozzle of the grease gun is clean before using. Pump a small amount of grease out of the dispensing nozzle and then wipe the nozzle off with a clean rag or lint-free cloth before attaching it to the grease fitting.
• Clean the grease fitting of all dirt before attaching the grease gun. Inspect and replace damaged fittings. It is helpful to use grease-fitting caps to keep them clean, but still wipe fittings clean before applying grease.
• Ensure that the proper grease is used at every grease point. Applying the wrong grease can cause an incompatibility problem, which can quickly cause bearing failure. Lubrication points should be clearly identified as to which grease is to be used. This can be done with colored labels, adhesive dots or paint markers.
• Grease guns should be stored unpressurized in a clean, cool and dry area and in a horizontal position to help keep the oil from bleeding out of the grease. Grease gun clamps make storage easy and organized. Also, cover the coupler to keep it free from dirt and contaminants.
• Calibrate grease guns regularly to ensure the proper delivery volume.

Anatomy of a Grease Gun

The lever is used in manual configurations of the grease gun for hand-pumping the grease from the barrel to the hose or tube.

The trigger and handle are used in manual configurations of the grease gun for hand-pumping the grease from the barrel to the hose or tube in a similar way as the lever.

The barrel is the exoskeleton of the grease gun that houses either the grease tube or the grease supplied from bulk storage.

The grease tube (or cartridge) is an inserted housing of grease that is replaceable when grease is depleted.

The hydraulic coupler (or connector) is the connection point that holds the hose or fixed tube attached to the head of the grease gun.

The head of the grease gun contains grease pathways and valves that allow the pumping of grease to travel from the barrel into the flexible hose or fixed tube.

The filler nipple is the injection point for grease from a filler pump.

The air-release nipple allows air to escape after new grease has been added to the grease gun and pumped into the head.

The spring provides the pressure onto the plunger.

The follower rod (piston rod, barrel rod, plunger rod) helps the plunger follow a uniform path as it keeps pressure on the bottom end of the grease tube. It also acts in pulling back the spring prior to inserting a new grease tube.

The follower handle offers a grip when pulling the follower rod prior to inserting a new grease tube.

The plunger provides uniform pressure to the back end of the grease tube as grease is depleted.

The flexible hose is used interchangeably with a fixed tube for flexible positioning of the connector or coupler.

The fixed tube is a rigid form of a flexible hose.

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Machinery Lubrication (4/2013)

About the Author

Bennett Fitch

  Bennett Fitch is a technical consultant with Noria Corporation. He is a mechanical engineer who holds a Machine Lubricant Analyst (MLA) Level III certification and a Machine Lubrication ... Read More

Grease Analysis: Early Warning System for Failures and Proactive Maintenance Tool

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29284/grease-analysis-system

Taking oil samples on a regular basis as part of a maintenance strategy has become state of the art. Oils are tested with regards to their condition, possible contamination and wear. Laboratory results and evaluations by experienced engineers can support the identification of upcoming component failures, prove whether maintenance actions like filtration or dehydration work properly and help establish condition-based oil drain intervals.

It’s a different story when it comes to grease. In the past, continuous trend-based grease monitoring was not a common practice even though the majority of installed bearings are grease lubricated and have a substantial impact on the reliability of the equipment. However, a change in philosophy seems to be occurring with a trend toward more routine grease analysis. This has been driven by technical issues and supported by positive experiences with oil analysis programs.

In addition, there have been many examples from the field where grease analysis has proven to provide important information about grease, including the amount of wear, contamination, consistency, bleeding behavior and condition of the base oil and additives.

Since grease properties often change significantly during operation and that the contamination and wear information is concentrated within a relatively small volume that’s not affected by filtration or diluted by a huge oil reservoir, grease analysis can be a very effective condition-monitoring tool. In many cases, grease analysis was initially performed only after damage or an accident, but trend analyses of grease samples have shown that trouble with grease or bearings can be recognized in advance with a good grease analysis program.

The Proper Sampling Technique

For a valid grease sample, the proper sampling technique is required. It obviously is much more difficult to take a representative grease sample from a bearing than to take an oil sample.

To take a grease sample, use a 
syringe to pull used grease
into the sampling tube.

To take a grease sample, remove the inspection screw on a slew bearing or take off the grease nipple from a rolling-element bearing. Cut the sampling tube in a length that is appropriate to enter the bearing and reach an area for taking a meaningful sample. Mount the clean tube on a syringe and press the opening of the tube onto the corresponding greased area. Use the syringe to pull the used grease into the sampling tube (at least 1 centimeter).

For some applications, it may be necessary to repeat the procedure on different sampling points of the same bearing. Approximately 1 gram of grease is enough for analysis. Be sure to watch for any color changes to avoid taking fresh grease too close to the regreasing point.

For trend analysis, samples should always be taken at the same points. A sample of the fresh grease should also be sent as a reference sample for all future analysis.

Elemental Analysis

Grease samples can be analyzed by optical emission spectroscopy (OES) according to the rotrode principle. Up to 21 elements can be evaluated to obtain information regarding wear, contamination and additives. These include:

• Wear metals (iron, chromium, tin, copper, lead, nickel, aluminum, molybdenum and zinc)
• Contamination elements (silicon, calcium, sodium, potassium and aluminum)
• Additives or thickeners (magnesium, calcium, phosphorous, zinc, barium, silicon, aluminum, molybdenum and boron)

Of special interest for diagnosing a bearing or grease condition is the amount of iron and chromium, which are present as wear particles from the bearing material. Non-ferrous materials like copper, lead and tin indicate corrosive or abrasive wear from the bearing cage. If dust (silicon or calcium) or sea water (sodium, potassium or magnesium) is present, this information can help determine the reason for the presence of wear metals. The amount of metallic soap elements or a comparison of the additive content in fresh and used grease can also reveal whether the recommended grease is in use.

Particle Quantifier

The particle quantifier (PQ) index is specialized for the determination of all magnetic iron particles. An index value between O and 9,999 characterizes iron particles present in the sample independent of the particle size. Because rust particles are non-magnetic, they are not measured.

The PQ index test is based on the principle that iron (and iron wear) is magnetic and can be detected by a magnet. If a grease sample contains magnetic iron wear particles, a magnetic field is disturbed. This change in the magnetic field can be measured.

Remember, the PQ index gives the total content of magnetic wear particles. Contrary to the iron wear information determined by OES, the PQ index provides information about all iron wear particles. Also, when using OES for used grease samples, only particles up to 5 microns can be detected because larger particles are not excited.

Grease Condition by FTIR

Fourier transform infrared (FTIR) spectroscopy identifies the type of base oil and thickener of the used grease. By comparing the unused fresh grease reference to the used grease sample, additive depletion or contamination by another grease type can be determined.

In comparison to FTIR spectroscopy of oil, the measurement and interpretation of a grease spectrum are more complex. The thickener compounds especially can be very dominant within important areas of the spectrum that are normally used for the calculation of the water content or oxidation.

FTIR spectroscopy is based on the principle that the molecules present in a lubricant can absorb infrared light at corresponding wavelengths depending on its typical structure. Changes in the used grease in comparison to the fresh grease reference spectrum are calculated on the typical peaks at predefined wave numbers and interpreted as oxidation, water, etc.

An FTIR spectrum can provide information regarding contamination
and any changes in a grease sample.

A very small grease sample (less than O.1 gram) is applied to an attenuated total reflectance (ATR) cell. In the contact zone, the grease sample will be exposed to infrared light. An infrared spectrum showing the absorbance of the infrared light on the corresponding wave number will be recorded and interpreted.

The infrared spectrum of a sample provides information regarding contamination and any changes in comparison to the reference spectrum. By a spectra subtraction of used grease with reference grease, the FTIR method indicates what kind of unknown grease is in use. In addition, a mixture of different greases in many cases is revealed. The identification of the original grease and the base oil type can be found by searching a library of reference spectra and can support the cause of a failure.

The FTIR method can also show whether synthetic or mineral base oils are used. If a mineral oil is used as the base oil, FTIR can indicate whether the base oil was oxidized because too much time passed without regreasing or because the temperature was too high. If the grease contains extreme pressure (EP) additives with zinc and phosphorus, the degradation of the additives can be seen. The water content in the grease may also be provided.

Water in Used Grease by Karl Fischer Titration

Besides solid contaminants, which can be identified by the OES elements silicon, calcium or aluminum, water is a type of contamination that is often the cause of corrosion. Typically, short regreasing intervals are the result of too much water. Unfortunately, determining the amount of water in grease is not as easy as in an oil sample.

For water determination according to the Karl Fischer method, a small grease quantity (approximately 0.3 grams) is placed into a glass vial and sealed with a septic cap. In a small oven, the sample is heated to approximately 120 degrees C. The steamed-out water is transferred by nitrogen into a titration vessel in which an electrochemical reaction between the water and a Karl Fischer reagent takes place. A titration curve is recorded, and the water content is defined precisely.

Depending on the grease type and application, the water content in the grease should not exceed the recommended values. Too much water in a grease can produce a variety of adverse effects, including corrosion on bearing metals, increased oxidation of the base oil, softening of the grease, and water washout of the grease.

If the result for water content according to the Karl Fischer method is compared to the elemental analysis by OES, it can be determined whether the water in the sample is “hard” or sea water, which contains minerals like sodium or potassium, or if it is soft water like condensate or rain water. If sodium, potassium, calcium and magnesium are found in the used grease but are not in the fresh grease, the presence of “hard” water is the likely reason. Comparing these two methods, Karl Fischer titration and OES, can also indicate whether the water was already present in the fresh grease as part of the production process.

Additional Tests

Besides the previously described methods, which should be the minimum requirement for grease analysis, there are a few other tests that can be performed. The table on the left lists most of these additional tests. Keep in mind that a failure investigation after damage has occurred often requires a more complex analysis, and not every test method is designed to be a routine analysis.

In summary, grease analysis has proven to be a useful tool to evaluate grease and bearing condition. Different situations and influencing factors for wear, contamination and grease condition have shown complex coherences between the grease analysis results and their practical meaning. This leads to the conclusion that observing and interpreting these factors with expert knowledge can enable proactive maintenance strategies to be applied in a reasonable way for grease-lubricated components.

Machinery Lubrication (2/2013)

Consider Consistency When Selecting Grease

Article extract from ReliabilityPlant newsletter:
http://www.machinerylubrication.com/Read/29223/selecting-grease-consistency

When instructing Noria’s Fundamentals of Machinery Lubrication course, I usually ask my students to tell me the type of grease that they currently use at their facility and not to give me a color. Most technicians understand that color doesn’t reveal much about a grease’s properties, but they don’t always answer correctly with the base oil viscosity, thickener and consistency.

Of course, greases are formulated with oil, thickener and additives. While you may be familiar with the formulation of grease, do you know what grease consistency means and how it should influence your grease selection?

Base Oil

Grease is formulated with up to 95 percent base oil. Most greases today use mineral oil as their fluid components. These mineral oil-based greases typically provide satisfactory performance in most industrial applications. In temperature extremes (low or high), a grease that utilizes a synthetic base oil will offer better stability.

Thickener

The thickener is a material that will produce the solid to semifluid structure in combination with the selected lubricant. The primary types of thickeners used in grease are metallic soaps. These soaps include lithium, aluminum, clay, sodium and calcium. Lately, complex thickener-type greases are gaining popularity. They are being selected because of their high dropping points and excellent load-carrying abilities.

Complex greases are made by combining the conventional metallic soap with a complexing agent. The most widely used complex grease is lithium-based. These greases are made with a combination of conventional lithium soap and a low-molecular-weight organic acid as the complexing agent.

Nonsoap thickeners are also gaining in popularity for special applications, including high-temperature environments. Bentonite and silica aerogel are two examples of thickeners that do not melt at high temperatures. However, there is a misconception that even though the thickener may be able to withstand the high temperatures, the base oil will oxidize quickly at elevated temperatures, thus requiring a frequent relube interval.

Notice in the table below how much the thickener percentage affects grease consistency. Keep in mind that there is a substantial amount of oil in the grease and that field conditions can also influence grease consistency.

Cone Penetrometer

Consistency

Grease consistency depends on the type and amount of thickener used along with the viscosity of its base oil. A grease’s consistency is its ability to resist deformation by an applied force. The measure of consistency is called penetration, which is contingent on whether the consistency has been altered by handling or working.

ASTM D217 and D1403 methods are used to determine the penetration of unworked and worked greases. To measure penetration, a cone of a specific weight is allowed to sink into a grease for five seconds at a standard temperature of 25 degrees C (77 degrees F). The depth, in tenths of a millimeter, to which the cone sinks into the grease is its penetration.

A penetration of 100 would represent a solid grease, while a penetration of 450 would be semifluid. The National Lubricating Grease Institute (NLGI) has established consistency numbers or grade numbers from 000 to 6 that correspond to specified ranges of penetration numbers.

Certain conditions will affect the consistency required for a grease. The table below can help you select the correct consistency for an application.

5 Categories of Penetration

Undisturbed - Grease that is in its original container.
Unworked - A sample that has received only minimal disturbance in being transferred from the sample can to the test cup.
Worked - A grease that has been subjected to 60 double strokes in a standard grease worker. NLGI classification is based on worked penetration.
Prolonged Worked - Grease that has been worked the specified number of strokes (more than 60), brought back to 77 degrees F and then subjected to an additional 60 double strokes in the grease worker.
Block - This is the penetration of a block grease, which is hard enough to hold its shape without a container.

Additives

Additives can play several roles in a lubricating grease. These primarily include enhancing the existing desirable properties, suppressing the existing undesirable properties and imparting new properties. The most common additives are oxidation and rust inhibitors, extreme pressure, anti-wear and friction-reducing agents.

In addition to these additives, boundary lubricants such as molybdenum disulfide (moly) or graphite may be suspended in grease to reduce friction and wear without adverse chemical reactions to the metal surfaces during heavy loading and slow speeds.

It’s important to note that speed and load help determine the proper viscosity required for an application. Remember, viscosity is the most important property of a lubricant. Whenever you are selecting grease, you must also take into consideration the application and match the required consistency to ensure that you provide the equipment with the best choice to improve equipment reliability.

Machinery Lubrication (12/2012)

Why You Should Inspect Bearing Grease Discharge

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29175/bearing-grease-discharge

There are three opportunities to inspect the state of in-service grease. One is by disassembly (such as by removing the bearing cap), the second is by sampling the grease using a probe (ASTM D7718), and the third is by examining the purge discharge. The purge discharge is the grease that’s extruded from exhaust ports, seals and other openings during relubrication or machine operation.


Not all grease-lubricated machines have a purge stream, but many do. Machines (mostly bearings) that purge grease provide a valuable opportunity for inspection. The opportunity is significant because of the frequency and simplicity of the inspection. Machines that purge are generally “total loss” systems, meaning the grease is not recovered for reuse but instead is discharged to a catch-pan, trap, grease thief, exterior surface or straight to the floor (Figure 1).

Using a Grease Discharge Trap

A grease discharge trap (GDT) is a perfect inspection device. One version of the GDT uses a simple barb fitting that is installed in the purge port (also known as a drain port, vent port or exhaust port). A 1½-inch zip-lock plastic bag (of various lengths) is positioned on the barb side of the fitting using an O-ring (see photos on the right). Grease that purges out of the fitting goes straight into the bag for easy inspection, disposal and sampling.

Reasons for Using the GDT

• Cleanliness - Purged grease is contained in the bag and not dispensed to the ground, floor or side of the machine.


• Disposal - Once the bag is full, it can be removed, sealed (using the zip-lock) and discarded. It is replaced with a new bag.


• Contamination Control - The machine is protected from contamination ingestion through the purge port during normal thermal air exchange and wash-down sprays.


• Unobstructed Purge Path - During machine operation, grease can freely purge to the trap to avoid excessive grease volume buildup in the bearing (heat generation and premature bearing failure).


• Inspection of Grease Discharge Volume- The trap enables easy inspection of the amount of grease discharge (too much or too little) from auto-lubers and manual lubrication practices.


• Inspection of Grease Condition - Look at the color of the grease including mixed colors (cross-contamination). Touch the grease through the bag to inspect for solids, grit and grease consistency. Slide a strong magnet on the outside of the bag to attract large wear particles.


• Grease Sample - Remove the bag with the grease discharge sample. Zip it tight, place in a sample bottle and send to a lab for analysis.

Following are examples of machines that commonly have a purge stream:

• Electric motor bearings
• Pillow-block bearings (conveyors, etc.)
• Some blower/fan bearings
• Some grease-lubricated gearbox bearings
• Mechanical couplings
• Some process pump bearings
• Some compressor bearings
• Hinge pins and some journal bearings
• Agitator bearings
• Some extruder bearings
• Some calender roll bearings

In many cases, purging grease through a bearing is not recommended, although it is commonly practiced. The decision to purge or not to purge should not be trivialized. To understand this better, see the sidebar below about purge versus volume control methods for lubricating bearings.

Figure 1. In total loss systems, grease is discharged to a catch-pan (left), exterior surface (right) or straight to the floor. Source: OilDoc

Too often the opportunity to inspect grease discharge is dismissed largely due to ignorance. In fact, there is a story to tell from the condition and state of grease discharge. This relates both to the state of lubrication and the health of the machine. There is also information to be learned about the application of the grease, the relube frequency and the relube volume that can be assessed by inspecting grease discharge.

What can be Learned from Purge Discharge

The discharge from bearings and other machine components is basically a sample of the grease condition as it exits (its terminal state). It carries out a historical account of the bearings. This includes debris from the bearing, contaminants the bearing was exposed to and degradation byproducts from the grease. The state of the discharge correlates to the quality and state of lubrication and ultimately the reliability of the bearing.

So what questions might the purge stream be able to answer? Take a look at the following list for examples:

Figure 2. This is an example of excessive lubrication.

Wrong or Mixed Grease - A wrong or mixed grease color can be observed in the discharge. An incorrect grease consistency might also be detected.
Degraded Grease - Evidence of oxidation (tar-like), thermal distress and/or dry, caky grease (oil loss) may be visible.
Contaminated Grease - Signs of water, corrosion, dirt or other impurities can be seen.
Inadequate Grease Volume or Frequency - This is shown from prematurely degraded and/or contaminated grease.
Excessive Grease Volume or Frequency - Large piles of grease discharge reveal problems (Figure 2).

When to Stop Pumping Grease into a Bearing

Bearings are often lubricated using a grease gun until a fresh grease purge is observed. While there are many cases when this is best practice, there are an equal number of cases when it is not.
Anyone who lubricates bearings with a grease gun should understand the alternative methods and when each should be applied. Of course, the machine or component manufacturer should always be consulted.
Noria refers to the two options as the Fresh Grease Purge method and the Grease Purge and Volume method. These methods and target applications are described below:

Fresh Grease Purge (FGP) Method

The bearing is lubricated until fresh grease emerges from the purge port (vent) or shaft/seal interface, or back-pressure is encountered. When to use the FGP method:

• Low speed-factor bearings (DNs less than 50,000) with a suitable purge path (purge port or shaft/seal interface)
• Bearings specifically designed for purge lubrication such as hinge pins, bushings, open bearings and some bearings with labyrinth seals
• Bearings exposed to high environmental contamination with a purge path (purge port or shaft/seal interface)

Grease Purge and Volume (GPV) Method

The bearing is lubricated until a pre-established maximum volume of grease has been introduced, fresh grease emerges from the purge port (vent) or shaft/seal interface, or back-pressure is encountered. When to use the GPV method:

• Electric motor bearings (i.e., electric motors that are intended to be periodically relubricated)
• Bearings with speed factors greater than 50,000 (DN)
• Bearings with no purge path
• Bearings with a possibly restricted purge path
• Bearings with an alternate purge path that could send grease to an unwanted internal compartment such as a lube oil sump

Cake-lock Conditions - The telltale sign of this condition is when the catch-pan only has oil. This means the thickener is binding up in the bearing.

Abnormal Wear Conditions - Visible evidence of wear debris is seen. Use a magnet to extract larger wear particles. Solvents can also be used to separate particles from the grease.

Figure 3. A grease thief (left) and a bellows-type grease discharge trap (right) can be connected
to a purge port.

Obstructed or Diverted Purge Path - The normal amount of grease discharge is not observed, meaning that grease is being diverted to another purge path.

Auto-Lube Malfunction or Neglected Grease Gun Relubrication - The normal amount of grease discharge is not seen, resulting in a potential starvation condition.

How to Inspect the Discharge

A quick, daily visual inspection is sometimes adequate. Look for abnormal grease discharge, color, consistency and location. Clean away the discharge so the amount of new discharge (since the last inspection) is easily recognized for inspection. Alternatively, use a simple grease discharge trap (see sidebar above). A discharge trap is a plastic bag, grease thief or bellows device connected to the purge port (Figure 3). Grease exhaust is held by the trap for later inspection, sampling and/or disposal.

Figure 4. A magnet placed under a gold pan or glass bowl can enable you to observe ferrous debris in a grease sample.

If the conditions of the discharge merit further inspection, consider the following:

• Lab Analysis - Many oil analysis labs can also analyze grease. Common tests include ferrous density, elemental spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Karl Fischer, oil content, analytical ferrography and others.


• Artist Spatula/Light Table Inspection - Use a common artist’s spatula to spread grease across a smooth glass surface. Is the grease soft, buttery, gummy, tar-like, crusty, cake-like, stringy or inconsistent in color? Shining a strong light from below the glass can help you identify clumps, wear debris, contaminants, etc.


• Particle Inspection - This can be done using solvents (e.g., toluene, mineral spirits, petroleum ether, etc.) to break down the grease. Separate the particles for visual or microscopic inspection by employing a gold pan, patch test or ferrogram method.


• Ferrous Density - Put some of the grease in a sample bottle along with solvents. Tape a strong magnet to the outside of the bottle and then shake. Observe the ferrous debris collection against the magnet. You can also place a magnet underneath a gold pan or glass bowl (Figure 4) and swirl.


• Oil Content - Load some of the grease sample in a small bushing the size of a thick wedding ring. Place this on blotter paper and examine the amount of oil that wicks out into the paper over a couple of hours. The damp zone relates to oil content. Try this with new grease first.

35%	of lubrication professionals never inspect the grease discharge from bearings and other machine components at their plant, based on a recent survey at machinerylubrication.com

The routine inspection and analysis of grease discharge should be a part of the skill set of operators and technicians responsible for lubrication, maintenance and machine reliability. The discharge carries bits and pieces of potentially valuable information. This could range from a clean bill of health to the remnants of a building internal machine graveyard.

Machinery Lubrication (10/2012)

About the Author

Jim Fitch

Jim Fitch, a founder and CEO of Noria Corporation, has a wealth of experience in lubrication, oil analysis, and machinery failure investigations. He has advised hundreds of companies on developing ... Read More