Textron Jacobsen SLF530, Repair Manual

Page: 210 / 352

6-16 673831-Rev A
HYDRAULICS
6
Lower Circuit Schematic and Theory
of Operation
System Conditions:
• Engine running
• Lift/lower joystick in the LOWER position
Oil Supply to Lift Valves
Hydraulic oil is drawn from the hydraulic oil tank by
section 1 of the gear pump assembly. Before entering the
gear pump assembly, the inlet oil is filtered by a
100-mesh screen to remove any debris. Operating
pressure oil from section 1 of the gear pump is routed
through the steering unit. The steering unit will supply oil
flow to the lift valve via port “E.”
Lower Circuit
Operating pressure oil supplied by section 1 of the gear
pump enters the lift valve at port “P.” The oil flows through
the solenoid valve to the pilot lines of the check valves,
the 450 psi (31 bar) relief valve, and to the piston side of
the front and center lift cylinders. Oil also flows to the
piston side of the rear lift cylinders. The 450 psi (31 bar)
relief valve allows sufficient pressure to build up to unseat
the check valves. Once that pressure is satisfied, the
relief valve will shift, dumping excess oil to the hydraulic
tank.
With operating pressure oil at the pilot lines of the check
valves, the check valves open. Gravity allows the cutting
units to lower, pulling against the lift cylinders. Oil from
the rod end of the front and center lift cylinders flows
through the 0.032 in. (0.
8 mm) one way orifices, which
dampen the lowering of the reels to prevent damage to
the cutting units, and then flows through the check
valves, and back to the hydraulic tank. Oil from the rod
end of the rear lift cylinders flows through the 0.026 in.
(0.66 mm) one-way orifices, which lowers the rear cutting
units at a slightly slower rate than the front cutting units,
then flows through the check valve, and back to the
hydraulic tank.
Circuit Relief
The lower system is protected by the 450 psi (31 bar)
relief valve. If the pressure on the pilot line of the relief
valve reaches 450 psi (31 bar), the valve will open,
dumping operating pressure oil through port “T” of the lift
valve to the hydraulic tank.