Copyright Goodheart-Willcox Co., Inc.
152 Hydraulic Systems for Mobile Equipment
Figure 6-39. A seized cylinder piston or gland can be difficult to remove. Hold the cylinder in a vise. Fill the cylinder
with oil. Install a pressure gauge and use a hydraulic hand pump to push the seized piston or gland out of the
cylinder. If the pressure reaches the cylinder’s limit, a new cylinder will need to be ordered and the old cylinder will
need to be scrapped.
Do Not Attempt to Stall a Hydraulic Cylinder or Motor under Pressure
While diagnosing and servicing hydraulic machines, technicians have at
times been tempted to mechanically limit or prevent an actuator from moving
while the actuator receives full hydraulic pressure and fl ow. This action must
be strictly avoided. While hydraulic components might appear to be small,
their output power can be tremendous.
A small hydraulic motor can easily produce 10 hp. Considering that a single
horsepower is the equivalent to 550 foot pounds per second, any attempt to
stall an actuator puts personnel at serious risk of injury. For this reason, techni-
cians must never attempt to mechanically stall, bind, or hold a hydraulic cyl-
inder or motor to prevent it from moving.
Do Not Attempt to Mechanically Actuate a Cylinder or Motor while
It Is under Pressure
Other injuries have occurred when technicians have attempted to mechan-
ically assist a stuck hydraulic motor to rotate while the motor is under pressure,
or assist a seized cylinder that is under pressure. These actions should also
be strictly avoided. If an actuator is inoperable, pressures and fl ows should
be checked, but technicians should never attempt to mechanically assist a
hydraulic actuator to move.