12M Series 3, 140M Series 3, 160M Series 3, 140, 150 and and 160 Motor Graders General Information (Steering System) Caterpillar


General Information (Steering System)
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1.1. Implement Pilot Oil Filter
2.1. Control Manifold
3.1. Shut-off Manifold
4.1. Hydraulic Tank
5.1. Piston Pump (Implement and Steering)
6.1. Pump Control Valve
7.1. Oil Filter (Hydraulic Return)
8.1. Joystick Controls
9.1. Steering Control Valve


Illustration 1g03505917
(1) Hydraulic tank
(2) Steering control valve
(3) Implement electronic control module (ECM)
(4) Joystick control
(5) Shutoff valve
(6) Steering cylinders
(7) Secondary steering pump
(8) Oil filter (hydraulic Return)
(9) Implement and steering pump and pump control valve
(10) Pilot control manifold
(11) Oil filter (pilot)

This module discusses the features and operation of the steering system. The following motor graders are covered in this module:

  • 12M Series 3 Motor Grader

  • 140M Series 3 Motor Grader

  • 160M Series 3 Motor Grader

The hydraulic system is a proportional priority pressure compensated system. The PPPC system is a load sensing system. The PPPC system uses a load sensing pump for the implement and steering in order to perform the pressure compensation function. The implement control valves have an internal flow compensator. This flow compensator performs the proportional priority function.

The steering system has the following main components:

  • Implement Pilot Oil Filter

  • Control manifold

  • Shut-off manifold

  • Hydraulic tank

  • Piston Pump (Implement and Steering)

  • Pump Control Valve

  • Oil Filter (hydraulic return)

  • Joystick controls

  • Steering control valve

  • Secondary steering pump

  • Implement electronic control module (ECM)

  • Steering cylinders

Implement Pilot Oil Filter

The pilot oil filter removes debris from the pilot oil for the implement solenoids.

Control Manifold

The pilot control manifold directs pilot oil to the solenoids of the implement system. The control manifold contains a main relief valve, a secondary steering relief valve, a pressure reducing valve, and a solenoid for the implement lockout switch. The control manifold also contains a pressure port and a pressure sensor.

Shut-off Manifold

The shut-off manifold contains a solenoid that will direct or inhibit pilot oil to the solenoids of the implement system based on the implement lock-out switch position in the cab. The shut-off manifold also contains a shuttle valve to send the appropriate load sense signal from the implement or steering system to the pump control valve.

Hydraulic Tank

The hydraulic tank stores oil for the hydraulic system.

Piston Pump (Implement and Steering)

The piston pump for the implement and steering is a variable displacement axial piston pump. When the engine is operating, the pump will produce flow in order to satisfy the following conditions:

  • The demand of the steering system

  • The margin pressure of the pump

  • The demand of the hydraulic implements

  • The internal lubrication of the pump components

Pump Control Valve

The pump control valve keeps the pump pressure and the pump flow at a level to fulfill the requirements of the implement and steering system.

Oil Filter (Hydraulic Return)

The return filter removes debris from the hydraulic system. The return filter prevents debris from entering the hydraulic tank.

Joystick Controls

The joystick controls send an electrical signal to the solenoids of the implement system and the steering system.

Steering Control Valve

The steering control valve directs the oil from the pump to the steering circuit and to the implement circuit.

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