ROD 7V8821 - Caterpillar

Pilot Hydraulic System
The pilot hydraulic systems consist of a gear type pilot oil pump that is driven by a shaft from the main hydraulic pumps, which are driven by the engine. Oil flow from the pilot pump is directed to the pilot oil filter and relief valve where the oil is filtered and the downstream pilot pressure is set. From the pilot oil filter, the pilot pressure oil flows to the pilot manifold. From the pilot manifold, pilot pressure oil is always made available to the operator joysticks and travel lever/pedals. Pilot oil is also supplied to various other components.When the hydraulic lockout lever in the operator compartment is in the LOCKED position, pilot oil is blocked. When the hydraulic lockout lever is in the UNLOCKED position, pilot pressure oil is sent to the operator controls, enabling implement operation and travel.The pilot manifold contains a number of subcomponents that will be discussed in greater detail in this manual. The pilot hydraulic system is divided into four basic circuits that utilize pilot pressure oil for the following functions:
Pilot control valves for implement and travel operation
Straight travel solenoid valve to ensure straight travel during implement operation
Two-speed travel operation to destroke the travel motors for high speed travel
Swing brake operation to release the swing brake during implement operationNote: Refer to the appropriate sections in this manual for more information.