Grease gun guide

What the PSI is for

Grease does not need thousands of pounds of pressure to flow into a healthy fitting. The pressure is for the fitting that has gone stiff: hardened grease in the channel, a ball that has stuck, a bearing that has not been fed since last season. The Bluebow kit develops 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. Once it moves, the pressure falls back to what the fitting takes.

If a fitting takes no grease at any pressure, stop. The ball is seized or the channel is blocked, and the fix is a new zerk, not more trigger. Forcing a fitting at full pressure is how a hose bursts or a coupler lets go.

What the flow rate is for

Flow is the figure for a day of fittings. The teal Bluebow kit moves 5.3 ounces a minute, the blue kit 7.05; on a tractor with dozens of zerks, or a baler before a day in the field, the difference is minutes per round. Both take their grease through a 39.4 inch flexible hose, which is what reaches the pivot behind a wheel and the fitting under a loader arm.

Figures are the ones each kit states for itself.

Bleeding air after a refill

A gun that has just been loaded carries pockets of air, and air under the plunger is why a fresh gun spits instead of flowing. The teal Bluebow kit names an air bleeder valve for this: after a refill, open the valve, pull the trigger until grease shows at the valve without bubbles, close it and go to the first fitting. On a gun without a valve, loosen the head a turn, pump until grease weeps at the thread and tighten it again. Either way, the first stroke at the fitting should be grease, not a hiss.

Two batteries and how far they go

Both kits ship with two 4.0 Ah batteries and a charger in the case. Run one and charge the other, and a day on a farm does not stop for the charger. The batteries are lithium cells, and the rules for them come from OSHA's bulletin on lithium battery devices and the U.S. Fire Administration: charge above freezing, keep them below about 130°F and out of a hot car, take them off the charger once full, store spares away from anything that burns, and take a battery that swells, smells or gets hot out of service and recycle it.

Why a grease gun can hurt a hand

Hand surgeons who study injection injuries report that it takes about 100 PSI to breach skin 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 small and 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. Keep your free hand clear of the coupler while the trigger is down, never test a hose or a fitting for a leak with a finger, and treat any puncture from a grease gun as a trip to a doctor the same day, however small it looks.

On a machine, the fitting is often near a moving part. OSHA counts lubricating and servicing among the maintenance activities covered by its lockout rule, which means the engine off and the key in your pocket before you reach into a loader arm or behind a belt.

Pressure, flow and the bleeding routine on this page are the figures the Bluebow lineup prints on both kits; the kits are on the grease guns shelf.