Farm and fleet
Why Your Grease Gun Spits After a Refill, and How to Bleed the Air Out
A freshly loaded grease gun hisses, spits and moves no grease, and the cure is thirty seconds at the bleeder valve. Here is what the air is doing, how to get it out, and why the same pressure that clears a fitting deserves respect from your other hand.
Every grease gun owner has stood at a fitting pulling the trigger while the gun hissed and nothing came out. The grease is in there. The problem is the air that came in with it, and until the air is out the plunger compresses air instead of pushing grease. The fix takes half a minute, and it is the same on the Bluebow cordless kit as on a hand gun, with one difference: the cordless gun has a valve for it.
Where the air comes from
Grease does not pour. When you load a cartridge or fill the barrel from a pail, pockets of air get trapped between the grease and the follower plate, in the head, and in the hose. On a hand gun the pump stroke compresses those pockets and lets them expand again, so the gun feels like it is working while the grease stays put. On a cordless gun the motor does the same thing faster: the trigger runs, the sound changes, and the coupler stays dry. A gun that spits in short bursts rather than flowing is a gun with air still in it, and more trigger does not help.
The bleeding routine
The teal Bluebow kit names an air bleeder valve on the head for this job, and the routine is the same on any gun that has one. Load the gun and screw the head back on. Open the bleeder valve a turn. Pull the trigger and watch the valve: first a hiss, then a mix of air and grease, then grease alone without bubbles. Close the valve and go to the first fitting. The first stroke at the fitting should be grease, not a hiss, and if it is not, open the valve and repeat.
- Load the cartridge or fill the barrel, and tighten the head.
- Open the air bleeder valve about one turn.
- Pull the trigger until the valve shows grease without bubbles.
- Close the valve and press the coupler onto the first fitting.
- If the first stroke hisses, open the valve again and repeat.
On a gun without a valve, loosen the head a turn, pump until grease weeps at the thread, and tighten the head again. Either way, the purpose is the same: give the trapped air a way out that is not through the coupler. Keep a rag under the head during the bleed, because the valve passes a little grease with the last of the air.
What 12,000 PSI is actually for
A healthy fitting does not need thousands of pounds of pressure. Grease flows into it at a fraction of that, and the pressure in the hose falls to whatever the fitting takes. The high figure on the box is for the fitting that has gone stiff: hardened grease in the channel, a ball that has stuck, a bearing nobody has fed since last season. Both Bluebow kits develop up to 12,000 PSI at the coupler, and the trigger lets you feel the moment the plug gives and fresh grease starts to move.
When a fitting takes no grease at any pressure, the answer is to stop. The ball inside is seized or the channel behind it is blocked, and the fix is a new zerk, which costs less than a cup of coffee, not more trigger. Forcing a fitting at full pressure is how a hose bursts at the crimp or a coupler lets go, and either one puts a jet of grease where your hand is.
| Kit | Flow | Pressure | Hose | Batteries |
|---|---|---|---|---|
| Blue | 7.05 oz/min | 12,000 PSI | 39.4 inches | Two 4.0 Ah |
| Teal | 5.3 oz/min | 12,000 PSI | 39.4 inches | Two 4.0 Ah |
Figures are the ones each kit states for itself.
Flow is the other number, and it is the number for a day of fittings rather than for one stubborn one. The blue kit moves 7.05 ounces of grease a minute and the teal kit 5.3. On a tractor with dozens of zerks, or on a baler before a day in the field, that difference is minutes per round. Both reach their fittings through a 39.4 inch flexible hose, which is what gets to the pivot behind a wheel and to the fitting under a loader arm, and both carry an LED under the head to find the zerk in the shade of a frame rail.
The injury hand surgeons see
This is the part worth reading twice. A paper by Dailiana and colleagues in the journal Hippokratia, on injection injuries, reports that breaching the skin takes about 100 PSI and that most high-pressure guns and injectors reach 2,000 to 12,000 PSI. Grease and oil are among the materials they see injected. The wound is a small puncture that is easy to dismiss, most such injuries hit the non-dominant index finger through inexperience with the equipment, and the risk of amputation is lower when surgical cleaning happens within six hours.
Read that against the kit on the bench: 12,000 PSI is the top of the range the surgeons describe, and the non-dominant index finger is the one steadying the coupler. So the rules are simple and absolute. Keep your free hand clear of the coupler and the hose end while the trigger is down. Never test a hose or a fitting for a leak with a finger. Never point the coupler at anyone. And if the gun ever punctures skin, however small the mark and however little it hurts, it is a trip to a doctor the same day, with the words high-pressure injection injury said at the desk. Grease under the skin does not stay where it went in.
Reading the trigger
The trigger on a cordless gun tells you more than a lever does. On a healthy fitting the motor runs at an even note and grease moves within the first second. On a plugged fitting the note drops as the pressure builds and the hose stiffens in your hand, and then one of two things happens: the plug gives and the note comes back up, or nothing changes. When nothing changes after a few seconds, the fitting is telling you it is blocked, and that is the moment to let go of the trigger rather than hold it down and wait for the hose.
Watch the coupler as well. Grease weeping around it means the coupler is not square on the zerk or the ball in the zerk is worn, and both leak pressure that should be going into the bearing. Reseat the coupler straight on, and if it still weeps with the trigger down, the zerk is the part to replace, not the coupler.
Lockout before you reach in
On a machine, the fitting is usually near something that moves. OSHA's lockout rule counts lubricating and servicing among the maintenance activities it covers, which means the engine off and the key in your pocket before you reach into a loader arm or behind a belt. On a farm there is no supervisor to make that call, so the habit has to be yours. The grease gun guide puts the same rules alongside the sources, and the farm set pairs the kit with the impact wrench for the rest of the season's maintenance.
Batteries and the end of the day
We ship both kits with two 21 V 4.0 Ah batteries and a charger. Run one and charge the other, and the gun does not wait for the charger. The batteries are lithium cells, and the rules for them come from OSHA's bulletin on lithium battery devices and from the U.S. Fire Administration: charge above freezing, keep the cells out of a hot cab and below about 130°F, take them off the charger once they are full, store the spare away from anything that burns, and retire a battery that swells, smells or runs hot to a fire-resistant container, then recycle it. A grease gun lives in a barn with hay and diesel, which is reason enough to keep those rules.
Wipe the coupler before the gun goes back in the case, because grease on the coupler picks up grit and grit goes into the next fitting. Leave the gun loaded: a cartridge keeps, and a loaded gun means the next round starts at the valve rather than at the pail.
