Jacobsen SLF 1880, Техническое руководство по ремонту

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8L-83
LOWER CIRCUIT SCHEMATIC AND
THEORY OF OPERATION
System Conditions:
• Engine running
• Mower lift lever in the LOWER position
Oil Supply to Lift Valve
Hydraulic oil is drawn from the hydraulic oil tank by
section 3 of the gear pump assembly. Operating pres-
sure oil from section 3 of the gear pump is routed to the
lift valve.
Lower Circuit
Operating pressure oil supplied by section 3 of the gear
pump enters the lift valve at port “P.” The oil flows
through the solenoid valve (lower position) to the pilot
lines of the check valves, opening the check valves,
and then flows against the 450 psi (31 bar) relief valve
and to the piston side of the 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 built up at the check valve
pilot lines, the check valves open. Gravity pulls the cut-
ting units down, pulling against the lift cylinders. The oil
from the rod end of the front and center lift cylinders
flows through the 0.032 in. (0.8 mm) 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) and 0.40 in. (1.0 mm) orifices causing the
rear lift cylinders to lower at a slightly slower rate than
the front cylinders.
Circuit Relief
The lower circuit is protected the 450 psi (31 bar) relief
valve located in the lift valve. If the lower circuit pres-
sure reaches 450 psi (31 bar), the pilot-operated relief
valve will open, allowing oil from the lower circuit to
bypass back to the hydraulic tank through port “T” of
the lift valve.