SERV1852-02
August 2008
TECHNICAL PRESENTATION
320D-336D HYDRAULIC EXCAVATORS -
TIER III ENGINES
PILOT HYDRAULIC SYSTEM
Service Training Meeting Guide
(STMG)
GLOBAL SERVICE LEARNING
320D-336D HYDRAULIC EXCAVATORS -
TIER III ENGINES
PILOT HYDRAULIC SYSTEM
AUDIENCE
Level II - Service personnel who understand the principles of machine systems operation,
diagnostic equipment, and procedures for testing and adjusting.
CONTENT
This presentation provides an introduction and describes the components and systems operation
of the 320D-336D pilot hydraulic system. Additional presentations will cover the machine
walkaround, engines, pumps and controls, main control valve group, swing system, travel
system, and tool control systems in more detail. This presentation may be used for self-paced
and self-directed training.
OBJECTIVES
After learning the information in this presentation, the technician will be able to:
1. identify the components and explain the operation of the 320D-336D hydraulic
excavators pilot system, and
2. diagnose problems in the pilot system.
REFERENCES
320D Hydraulic Excavator Specalog AEHQ5856
324D Hydraulic Excavator Specalog AEHQ5663
325D Hydraulic Excavator Specalog AEHQ5665
328D Hydraulic Excavator Specalog AEHQ5706

- The nomenclature for the 325D MH and 330D MH did not change.
- The nomenclature for the 325D FM and 330D FM did not change.
- The 325D HD HW did not change into 329D HD HW. This model is being discontinued.
However, the 330D HD HW changed to the 336D HD HW.
SERV1852-02 - 4 - Text Reference
08/08 Pilot System
1
INTRODUCTION
The oil delivered from the pilot pump performs the following main functions:
- Provides pilot oil pressure to the pilot control valves for implements, swing, and travel in
order to perform machine operations.
- Provides pilot pressure oil in order to control the output flows of the main pumps.
- Provides pilot pressure oil in order to automatically operate the control devices.
The pilot circuit is classified into the following circuits and each circuit performs one of the
above functions:
- pilot control valve circuit - power shift pressure system
- pressure switch circuits - straight travel valve circuit
- swing parking brake - boom priority
- swing priority - automatic travel speed change
- heavy lift setting of the main relief valve
SERV1852-02 - 5 - Text Reference
08/08 Pilot System
Stick Cylinder
Bucket Cylinder Boom Cylinders
Swing Motor Travel Motors
Pilot
Control
Valves
Priority
Valves

SERV1852-02 - 7 - Text Reference
08/08 Pilot System
1
2
3
4
5
3
The filter element in the pilot oil filter removes contaminants from the pilot oil.
If the pilot oil is extremely cold or if the flow of pilot oil through filter element becomes
restricted by contaminants, the oil bypasses the filter element through the bypass relief valve.
The bypass relief valve is built into the pilot oil filter base.
The pilot oil flows from the pilot pump to inlet port. When the pressure in the pilot oil system
reaches the pressure setting of the pilot relief valve, part of the pilot oil flow is returned to the
hydraulic tank. The pressure of the pilot system oil in outlet lines is equal to the pressure
setting of the pilot relief valve.
SERV1852-02 - 8 - Text Reference
08/08 Pilot System
Pilot System
Relief Valve
Pilot System
Filter
Pilot Filter
Relief Valve
Pilot System
Relief Valve
Pilot System
Filter
Pilot Filter
Relief Valve