Photo of a lever grease gun lying on a steel workbench beside a plain grease cartridge in a service bay.

How to Load a Grease Gun Without Air Pockets

A grease gun that won't pump leaves you standing at a fitting with a machine that needs lubrication and a tool that won't do its job. Often the problem is how the gun was loaded, not the gun.

Milton® has made tools for working shops since 1943. This guide covers how to load a grease gun three ways (cartridge, bulk grease and filler pump), how to prime it so air pockets don't stop it, and what to check when it still won't pump.

The Short Version

How to load a grease gun: unscrew the head from the barrel, put in a cartridge open end first or fill the barrel with bulk grease, screw the head back on, then prime the gun until grease flows from the coupler.
Trapped air is a common reason a freshly loaded gun won't pump. Priming pushes it out.
Check which loading methods your gun supports: cartridge, suction fill or filler pump. Not every gun takes all three.
Wear safety glasses. The grease and the cartridge in the barrel are under spring pressure when you open it.

What to Check Before You Load a Grease Gun

Your gun's manual comes first, because models differ. The steps below follow NAPA's operating instructions for its lever style grease gun, and the notes on air operated guns follow Matco's manual for its PGG air operated gun.

Start with safety and wear safety glasses. The spring inside the barrel keeps the grease and the cartridge under pressure, so open either end of the barrel with care.

Next, check the air supply. If your gun runs on shop air, disconnect the air before you load it. Run it on dry air through a filter, regulator and lubricator (FRL) unit, because moisture in the air damages the gun. Check your gun's air range too: the PGG, for example, runs on 40 to 120 psi and recommends 90. Our guide to sizing pneumatic FRL systems covers that part of the line.

Last, work out which loading method your gun takes by looking at its head. A loader fitting or filler plug on the head means the gun takes grease from a filler pump. Without one, load by cartridge, or by suction fill if your manual allows it.

How to Load a Grease Gun with a Cartridge

Unscrew the head from the barrel.
Connect the rod to the rubber plunger by giving the rod handle a quarter turn while you pull it.
Pull the rod handle back and lock it. Handles come in two styles: lock tabs that pass through the end cap, or a grooved handle that seats in a slot.
Remove the plastic cap from the cartridge and insert the cartridge into the barrel, open end first.
Push the cartridge in until the rim of the pull tab end meets the rim of the barrel, then peel off the pull tab seal.
Screw the head back onto the barrel.
Release the rod handle from the end cap. You should feel resistance when you push on it, which tells you the rod is still connected to the plunger.

Now prime the gun. On a brand new gun, remove the plunger assembly the first time and coat the outside of the rubber plunger with a heavy layer of grease.

Photo of a grease cartridge partly slid into the open barrel of a lever grease gun, with the head unscrewed beside it.

How to Fill a Grease Gun from a Bulk Tub

Suction fill loads the barrel straight from a tub of grease. It only works on guns that allow it, so check your manual. If there is a cartridge in the barrel, take it out first.

Unscrew the head from the barrel and pack the head with grease.
Connect the rod to the rubber plunger.
Put the open end of the barrel about 2 inches into the grease.
Pull the rod handle slowly while you push the barrel deeper into the grease.
When the rod is fully extended, lock it in place.
Screw the head onto the barrel and release the rod handle.

Wipe the grease off the outside of the barrel, then prime the gun. Clean up any spills as well, because grease left on floors, tools or equipment is a slip hazard.

How to Fill a Grease Gun with a Filler Pump

A filler pump fills the barrel through a fitting on the head, so it only works on guns with a loader fitting or a filler plug. A gun with a filler plug needs a loader fitting that matches the valve on your pump. Fittings and valves come in three industrial standard sizes, so check the match first.

Wipe the loader fitting clean.
Connect the rod to the rubber plunger, then push the rod fully into the barrel.
Insert the loader fitting on the head into the valve on the pump.
Operate the pump until the barrel is full. The rod will be fully extended and the tabs on the rod will show.
Remove the loader fitting from the pump valve.

Don't overfill, because too much grease can leak from the joints. Then prime the gun.

How to Prime a Grease Gun and Get the Air Out

Priming pushes the air out of the head so grease can reach the coupler. Do it after every load. The method depends on your gun.

Gun	How to prime it
Lever gun with an air relief valve	Press the air relief valve while you push the rod handle.
Lever gun without an air relief valve	Loosen the head slightly, push the rod handle to expel the air, then retighten the head.
Air operated gun	Leave the head 2 to 3 turns loose, move the plunger rod back and forth to push out the air pockets, connect the air, then press and release the trigger until grease comes out of the nozzle. Tighten the head fully once the gun is primed.

On a lever gun, you can keep pressure on the rod handle while you prime by standing the gun on a workbench and pulling down on the barrel as you pump the lever. On an air operated gun, press and release the trigger rather than holding it down, and don't work it too fast, because the piston has to finish a full cycle before the next one starts.

Once the gun is primed, disconnect the rod from the plunger and push the rod all the way into the barrel. Pump the lever several times until grease flows from the coupler.

Photo of a lever grease gun on a steel workbench with a bead of fresh grease at the coupler tip and a grey shop rag beside it.

Why Won't My Grease Gun Pump After Loading?

Start with the cheapest checks: is there grease in the barrel, and is the head tight? Then work down this table.

Problem	Likely cause	What to do
Gun won't dispense grease	The cartridge or barrel is empty	Replace the cartridge or refill the barrel.
Gun won't dispense grease	Air is trapped in the head	Prime the gun again, using the method for your gun in the section "How to Prime a Grease Gun and Get the Air Out".
Air operated gun pumps little or no grease	The barrel isn't fully tightened	After priming, tighten the barrel completely.
Gun pumps little or no grease	The extension is blocked	Remove the extension and run the gun. If grease flows, clean or replace the extension.
Gun pumps little or no grease	The grease is too thick or cold	Keep the gun and grease away from extreme cold, or use a thinner grease.
Cartridge won't empty completely	The tabs on the rod are binding on the plunger	Connect the rod to the plunger and push the rod in as far as it goes. Measure from the end cap to the tip of the rod handle. More than 1-3/4 inches means the cartridge isn't empty.

FAQ

How do I connect an air operated grease gun to shop air?

Fit the quick connect coupler supplied with the gun, and make sure it matches the female coupler on your air line. If it doesn't, use a coupler that does. The air fitting has 1/4 inch NPT threads, so thread it into the handle with thread sealant or PTFE tape and tighten it so air can't leak.

How do I lubricate an air operated grease gun?

Run it on an air line with a lubricator, or add a few drops of oil through the air inlet. Use SAE 30 or heavier. A gun that cycles very slowly may need lubrication in the pumping chamber.

How tight should the grease gun extension be?

Snug, not tight. Over-tightening puts stress on the die cast outlet and can fracture it. Use thread sealant for a leak proof joint.

Next Step

Choosing a gun? Start with how you plan to load it: cartridge, suction fill or filler pump. Browse Milton grease guns and grease fittings, or contact us for help matching a gun to your shop.

Filed in: Grease guns and lubrication

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