Operator`s manual

MAINTENANCE MANUAL

SECTION 5

5. HYDRAULIC SYSTEMS

5.1 GENERAL

The main hydraulic pump (see Figure 5-1, number 1) is operated by a power-take-off (PTO)(2) from the

truck engine. The PTO is selected by a switch located in the cab. When the PTO switch is moved to the

"ENGAGED" position, a pneumatic circuit is energized which engages the PTO with the engine. For a

description of the Pneumatic circuit refer to "Pneumatic System" Section 7. When the PTO is engaged,

the red indicator light in the cab will be lit.

NOTE: Concurrent with the engagement of the PTO, the Ladder Securing Clamps will release.

The paragraphs that follow describe the operation of the outrigger and ladder hydraulics. The numbers in

brackets refer to locations on Figures 5-2 and 5-2-1, the Hydraulic Schematic.

5.2 MAIN POWER

With the truck engine idling and the PTO engaged, the main pump (7) is running and draws oil through a

filter (2) from the reservoir (1) and pumps the oil through a check valve (10). The check valve prevents

the flow of oil to the main hydraulic pump when either the electric pump (8) or hand pump (9) is used and

check valves (11) prevent the flow of oil through the auxiliary pumps when the main pump (7) is operating.

The oil is then pumped through the selector valve (12) and flows either to the outrigger control valves (50)

and returns to the reservoir (1) after passing through a filter (4), or flows via the main joint (13) to the

Relief/Unloader Valve (14) which opens and allows