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Groundsmaster 4500--D/4700--DHydraulic System Page 4 -- 26
Cutting Deck Blade Braking
When the operator turns the PTO switch OFF (or if the
decks are raised), deck manifold solenoid valves
(PRV1, PRV2, SV1 and SV2) are de--energized. The
valves will shift to direct oil away from the deck motors
and toward the oil cooler and filter. Hydraulic pressure
is reduced to the c utting deck motors which slows the
cutting blades and also allows the deck manifold relief
valve (RV) to shift. The shifted relief valve removes the
flow path from the orifice at the logic cartridge, causing
the logic cartridge to shift and block the return oil path
from the deck motors (Fig. 20).
Theinertia oftherotating cuttingblades, however,effec-
tively turns the deck motors into pumps causing an in-
crease in pressure as the flow from the motors comes
up against the closed logic cartridge (LC). When this
pressure builds to approximately 1500 PSI (104 bar),
thereliefvalveopens whichallowsasmallamount ofhy-
draulic flow past the relief valve (Fig. 21). This flow
causesapressureincreasethatshiftsthelogiccartridge
to once again allow oil flow from the deck motors (Fig.
22). When return pressure drops below 1500 PSI (104
bar), the relief valve reseats and causes the logic car-
tridge to close again, blocking return flow from the deck
motors to further slow the cutting blades. This action of
the relief valve opening and the logic cartridge shifting
occurs several times in a very short time frame as the
blades finally come to a stop. Once the blades have
stopped, the logic cartridge remains in the neutral posi-
tion to keep the deck motors from rotating.
Figure 20
TO OIL
FROM
COOLER
GEAR
PUMP
ORIFICE
Figure 21
TO OIL
FROM
COOLER
GEAR
PUMP
ORIFICE
Figure 22
TO OIL
FROM
COOLER
GEAR
PUMP
ORIFICE