"How can I keep the pressure from my grease gun low to avoid damaging components?"
The key principle to remember for a fixed output grease gun (which covers nearly
all grease guns) is this: grease volume and pressure vary with the speed lever
stroke.
If the grease gun lever is worked quickly, the momentary
surge of grease flow through a fixed chamber increases the discharge
pressure,
and will localize
the pressure toward the path of least resistance. In a motor bearing cavity,
this could cause the grease to surge through clearance gaps toward the winding,
or perhaps press the cage into the roller.
In a pillow block bearing, the
directional pressure of the grease flow could cause the grease to rupture
the shield clearance
or escape through a lip or labyrinth seal, preventing the uniform replenishment
of grease through the bearing.
A slow, uniform press of the level can help minimize this
risk, regardless of the rated output of the grease gun. If the lever
is worked slowly, pressure
is uniformly distributed throughout the chamber.
If the bearing cavity is full and grease is applied under
pressure, the grease will pressurize until either the grease passes through
a weak point in the bearing or until the grease gun reaches maximum pressure
and the lever cannot be moved any further.
Because an off-the-shelf, general-purpose grease gun can
generate pressures in the order of 7,000 PSI, it stands to reason that
the grease will either find a weak point to
pass, or will rupture a clearance, seal or passageway and create a
new weak point.
To avoid this, the lube technician may need
to
install and use a pressure gauge on the output side of the grease
gun, or "sense" the change in pressure based on resistance at the handle.
Once resistance is reached, the lube technician will choose to disconnect
the gun and ‘waste’ the remaining stroke.
Zerk fittings with pressure
shut-off valves can be most helpful at reducing over-pressurization
of cavities. A 500 PSI limit is desirable for the great majority of applications.
Mike
Johnson, Noria Corporation
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