Toro Groundsmaster 4300-D Service Manual page 90

Lower the Cutting Decks (continued)
Counterbalance/Float
Hydraulic System: Hydraulic Flow Diagrams
directed to the barrel end of all lift cylinders to extend the cylinders and lower the
cutting decks. The 4 fixed orifices in the lift control manifold (C2, C4, C6, and
C8) control the lowering speed of the cutting decks by providing a restriction for
the return flow from the lift cylinders.
While the cutting decks are being lowered, the proportional relief valve (PRV)
has a secondary function as a circuit relief to limit lift cylinder circuit pressure
to 13,800 kPa (2,000 psi). The lift cylinder circuit pressure can be monitored at
lift control manifold port G4.
When the cutting decks are fully lowered, the lift manifold valves (S1 and PRV)
are de-energized (Figure
hydraulic flow to return to tank through the manifold. This flow through the
pressure relief valve causes a pressure differential that shifts the logic cartridge
(LC) which allows the majority pump flow to bypass the lift cylinders. The lift
manifold valve S2 remains energized when the cutting units are fully lowered to
allow fluid flow to and from the lift cylinders. The bidirectional flow is necessary
for proper cutting deck counterbalance/float operation.
Once the cutting decks are fully lowered, the lift control manifold solenoid
valve (S2) remains energized and the proportional relief valve (PRV) is used to
maintain an amount of pressure (counterbalance) on the rod ends of the deck
lift cylinders (Figure 37). This counterbalance pressure transfers cutting deck
weight to the machine to improve the traction.
A pressure transducer located in the forward traction hydraulic tube is used by
the controller as an input to determine traction circuit pressure. Based on the
transducer input and the machine counterbalance setting, an electrical output
from the controller is provided to the lift control manifold proportional relief valve
(PRV) to vary the counterbalance pressure. As the traction pressure increases
(e.g., climbing a hill) the counterbalance pressure also increases to increase the
weight on the tires and improve traction. The counterbalance setting can be
adjusted to L , M
OW EDIUM
Display (page 5–7) or the Traction Unit Operator's Manual.
37). The de-energized relief valve (PRV) allows
, and H via the InfoCenter display; refer to
IGH
Page 4–28
InfoCenter
Groundsmaster ® 4300-D
16226SL Rev C