
4
Excavator Supplement for 3066 Engine
Disassembly and Assembly Section
Disassembly and Assembly
Section
Hydraulic System Pressure -
Release
SMCS Code: 3000-553-PX; 4250-553-PX;
4300-553-PX; 5050-553-PX
Pressure Release Procedure
The release of hydraulic pressure in an hydraulic
circuit is required before service is performed to
that hydraulic circuit. Release the pressure in the
following hydraulic circuits before any hydraulic
lines are disconnected from that hydraulic circuit or
hydraulic components are removed.
• Boom hydraulic circuit
• Stick hydraulic circuit
• Bucket hydraulic circuit
• Swing hydraulic circuit
• Travel hydraulic circuit
• Attachment hydraulic circuits (if equipped)
• Pilot hydraulic circuit
• Return hydraulic circuit
Release Of Hydraulic Pressure From A
Single Hydraulic Circuit
WARNING
Personal injury can result from hydraulic oil pres-
sure and hot oil.
Hydraulic oil pressure can remain in the hydraulic
system after the engine has been stopped. Seri-
ous injury can be caused if this pressure is not re-
leased before any service is done on the hydraulic
system.
Make sure all of the attachments have been low-
ered to the ground, and the oil is cool before re-
moving any components or lines. Remove the oil
filler cap only when the engine is stopped, and the
filler cap is cool enough to touch with your bare
hand.
NOTICE
Care must be taken to ensure that fluids are contained
during performance of inspection, maintenance, test-
ing, adjusting and repair of the product. Be prepared to
collect the fluid with suitable containers before open-
ing any compartment or disassembling any compo-
nent containing fluids.
Refer to Special Publication, NENG2500, "Caterpillar
Tools and Shop Products Guide" for tools and supplies
suitable to collect and contain fluids on Caterpillar
products.
Dispose of all fluids according to local regulations and
mandates.
Perform the following Steps in order to release the
hydraulic pressure from a single hydraulic circuit of
the main hydraulic system.
1. Position the machine on level ground.
Illustration 1
2. Fully retract the stick cylinder rod. Adjust the
position of the bucket so that the bucket is
parallel to the ground. Lower the boom until the
bucket is flat on the ground. Refer to Illustration
1.
3. Shut off the engine.
4. Turn the engine start switch to the ON position
without starting the engine.
5. Place the hydraulic activation control lever in the
UNLOCKED position.
6. Move only the joysticks or the pedals of the
hydraulic circuit that requires service to the FULL
STROKE positions. This will release the high
pressure only in that single hydraulic circuit.
This will also release any pressure that might be
present in the pilot hydraulic circuit.