M318 Excavator Hydraulic System General Testing and Adjusting Information Caterpillar


General Testing and Adjusting Information
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1.1. Location of Pressure Taps
2.1. Suggested Test Sequence
3.2. Implement Hydraulic System
4.2. Swing System
5.2. Travel System

------ WARNING! ------

Hydraulic oil pressure can remain in the hydraulic systems after the engine and pump have been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic systems. To prevent possible injury, refer to the section, Testing and Adjusting, "Hydraulic System Pressure - Release" before any fitting, hose or component is loosened, tightened, removed or adjusted.

When possible, the work tool must always be lowered to the ground before service is started. When it is necessary for the boom to be in the raised position while tests or adjustments are done, be sure that the boom, stick and work tool have correct support.

The swing lock (if equipped) must be engaged before service is started.

Always move the machine to a location away from the travel of other machines. Be sure that other personnel are not near the machine when the engine is running and tests or adjustments are being made.

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The correct oil temperature, flow, and pressure are necessary for correct operation. Pump output (oil flow) is a function of engine speed (rpm) and valve adjustment. Oil pressure is caused by resistance to the flow of oil.

Each of the work tool circuits contains a check valve which prevents cylinder drift while the main control valve spool is in the NEUTRAL position.

Each of the work tool circuits contains makeup valves that provide makeup oil to the head end or to the rod end of the cylinder and to both ends of the motor.

Each of the cylinder circuits contains line relief valves for cylinder extension and retraction. The swing motor circuit contains line relief valves for swinging the upper structure right or left.

Visual checks and measurements are the first steps during troubleshooting. Refer to Testing and Adjusting, "Visual Inspection". Next, perform the operational checks. Refer to Testing and Adjusting, "Operational Checks". Finally, perform the required tests and adjustments on the machine.

Location of Pressure Taps




Illustration 1g00814819

Pressure taps are located in the battery compartment.

(1) Main pump pressure

(2) Load sensing signal pressure

(3) Accumulator pilot pressure

(4) Proportional reducing valve pressure (Main pump)

(5) Swing pump pressure

(6) Steering pressure

(7) Wheel brake accumulator charging pressure

(8) Swing brake pressure

(9) Attachment circuit pressure

Suggested Test Sequence

Tests in this manual should be performed in a specific sequence. The sequence depends on the system that is being tested. This section covers the major systems. This manual contains other tests that are not listed in this section.

Implement Hydraulic System

  • Engine Speed

  • Relief Valve (Pilot)

  • Margin Pressure and Low Pressure Standby

  • Relief Valve (Signal Limiter)

  • Main Pump (Proportional Reducing Valve)

  • Main Pump (Destroke Pressure)

  • Engine Performance

  • Engine Load Speed

  • Relief Valve (Main)

  • Main Pump (Flow)

Swing System

  • Relief Valve (Swing Charge Pressure)

  • Swing Pump Control (Mechanical Zero)

  • Swing Pump Control (High Pressure Cutoff)

  • Solenoid Valve (Swing Pump Proportional Relief)

  • Relief Valve (Swing Pump)

  • Swing Brake Pressure

Travel System

  • Travel Motor (Stall Pressure)

  • Travel Motor (Upstroke Pressure)

  • Travel Motor (Drive Shaft Speed)

  • Relief Valve (Line) (Travel Motor)

  • Transmission (Shift Pressure)

  • Transmission (Parking Brake Reserve Pressure)

Information System:

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