Mastering the Grease Gun: Essential Practices for Effective Lubrication

Grease guns seem simple enough. But how well do you know yours? Do you know how to correctly cartridge and bulk load your gun? Do you know how to expel trapped air from it? Do you know its shot size in cc or cu in (e.g., in cubic centimeters or cubic inches)?

Do you know how much pressure your gun can develop? If you don’t, you’re not alone.

In reality, many grease-gun operators have never been adequately trained to correctly fill a grease gun or determine its output or pressure.

Since most of these devices are now being manufactured offshore, they rarely come with specification sheets or quality instructions. Let’s examine some best-practice user fundamentals associated with these lubrication workhorses.

Grease-Cartridge Loading

Most of the grease guns that are purchased these days use grease cartridges. To load a new cartridge correctly:

1. Wipe the grease gun clean with a lint-free rag.
2. Unscrew the grease gun head from the barrel and place it on a clean surface or paper towel.
3. Firmly hold the grease barrel in one hand and pull back the rod handle at the end of the barrel with the other hand until it can go no further and lock into position. NOTE: Depending on the rod style, it may have a friction-lever lock built into the end of the barrel that automatically holds the rod in place when extended. Or, the barrel end may have a slotted hole that requires the extended rod to be positioned across the slot into the locked position.
4. Carefully remove the spent cartridge from the open end of the barrel, taking care not to cut a finger with the sharp open edge of the spent cartridge.
5. Place the barrel next to the head on a clean surface.
6. Ensure the new grease cartridge is filled with the same grease as the old cartridge. If not, the grease gun must be thoroughly degreased and cleaned to ensure bearings are not cross-contaminated with two different greases.
7. Pull the plastic end cap off the grease cartridge and insert the cartridge into the grease-gun barrel open end first. Once fully inserted, remove the pull-tab foil end from the cartridge.
8. Fully screw the grease gun head back on the barrel and back off (loosen) one turn.
9. Release the rod handle by pushing the friction-lock lever or returning the lever rod back across the slot to its center position, then slowly push the rod back in place in the barrel as far as it will go.
10. Pull the trigger or pull/push the lever until grease begins to dispense, then securely tighten the gun head.
11. If no grease flows, an airlock is likely to blame. To release trapped air, pump the grease gun a couple of times, then, if fitted on the grease head, push the air-release valve and re-pump the grease gun. If grease still doesn’t appear, repeat the process. On smaller grease guns with no air-release valves, back off (loosen) the barrel a couple of turns, and pump until grease appears, then retighten the barrel,
12. Wipe the grease gun with a lint-free cloth, then place all spent materials in a contaminated waste container for removal.

Bulk-Loading Grease

Some grease guns have a dual-fill feature, whereby the barrel can accommodate a standard grease cartridge or be bulk-loaded. For such guns and those designed specifically for bulk loading:

1. Wipe the grease gun clean with a lint-free rag,
2. Unscrew the grease-gun head from the barrel and place it on a clean surface or paper towel.
3. Immerse the open end of the grease barrel into the bulk-grease container and slowly plunge it into the grease while drawing back the rod handle until it is fully extended and the grease barrel is full.
4. Alternatively, the barrel can be hand-packed from the open end with the rod extended and locked. NOTE: This fill type can be messy and prone to dirt and air inclusion.
5. Fully screw the grease-gun head back on the barrel and back off (loosen) one turn.
6. Release the rod handle by pushing the friction-lock lever or returning the lever rod back across the slot to its center position, then push the rod back in place in the barrel as far as it will go.
7. Pull the trigger or push/pull the lever until grease begins to dispense, then securely tighten the gun head.
8. If no grease flows, an airlock is likely to blame. To release trapped air, pump the grease gun a couple of times, then, if fitted on the grease head, push the air-release valve and re-pump the grease gun. If grease still doesn’t appear, repeat the process. On smaller grease guns with no air-release valves, back off (loosen) the barrel a couple of turns, pump until grease appears, and then securely retighten the barrel.
9. Wipe the grease gun with a lint-free cloth, then place all spent materials in a contaminated waste container for removal.

Output and Delivery Matters

A grease gun is a simple design based on basic hydraulic pump principles. Depending on your device’s internal design, a few strokes of the trigger or lever can produce an astounding delivery pressure (ranging from 2500 to 15,000 psi).

With that type of output pressure and lack of grease-delivery knowledge and discipline, it can be easy for an untrained grease gun operator to destroy bearing seals and over-lubricate bearings, which, in turn, can result in premature bearing failure and downtime.

Sadly, grease-gun output pressure is rarely stamped on these devices. A simple pressure-test rig can be constructed using a fixed 20,000-psi hydraulic gauge connected to a grease fitting. Connect the grease pump to the fitting and perform a “dead head” pump to see and record the generated pressure.

To measure the grease-pump-delivery output, purchase a test tube marked in cubic centimeters or cubic inches and pump in 10 shots of grease (One complete lever or trigger cycle equals one shot). Divide the total amount shown in the test tube by 10 to arrive at the actual shot size.

For example, if the test tube showed 27 centimeters of grease, the actual shot size would be 27/10 = 2.7 cc. (Pneumatic- and battery-operated grease-gun shot size can be calibrated the same way or by hooking these types of devices up to a flow-metering device.)

Note: Grease guns aren’t all built to the same design specifications. Therefore, their displacement-output volumes, or “shot” sizes, will likely differ. This poses enormous problems for a plant when a PM task calls for two shots of grease and the guns used at the site haven’t been standardized.

Remember that two shots of a 3-cc-displacement gun will deliver six times more lubricant than two shots of a 1/2- cc-displacement gun.

Some grease-gun manufacturers confuse the delivery-output issue by marketing grease-gun-reservoir capacities and “shot” displacement by weight (in grams and/or ounces).

On the other hand, grease manufacturers use different ingredients and formulations for each grease type, resulting in different specific gravity ratings and weights. This means that similar volumes of grease can have different weights.

For example, greases can be marketed in a standard grease-gun cartridge with the same volume, but one cartridge might weigh 300 grams while another weighs 400 grams. Bearing-fill cavities are measured in volume, not weight. Therefore, always use volume displacement as your grease unit of measure.

Finally, once a grease gun’s pressure and shot size are known, it’s essential to print out a tag with that information and attach it to the gun.

Cleaning and Storage Practices

After a grease gun has been used, it should be cleaned and made ready for its next assignment. Be sure to store it vertically in a grease caddy. These types of caddies can be magnetized to your toolbox or metal cupboard or screwed to a wall.

This type of vertical storage will ensure your lubrication workhorse remains free of damage, dirt, and, importantly, cross-contamination from other grease guns.